Polyelectrolyte hydrogel formulations and methods for making and using the same

Abstract

Described herein are polyelectrolyte (PE) hydrogels that have properties suited for numerous medical applications. The polyelectrolyte hydrogels are composed of a mixture of one or more water soluble polycationic polyelectrolytes, one or more water soluble polyanionic polyelectrolytes, and monovalent and / or divalent ions. Depending on the selection and the amount of polycationic polyelectrolyte, the polyanionic polyelectrolyte, monovalent and / or divalent ions, charge ratio, and inclusion of any additional additives or components, the mechanical properties, durability, deliverability, size of vessel occluded, and clotting efficacy can be adjusted to fit the intended application. The PE hydrogels remain dimensionally stable and insoluble in physiological conditions.

Description

POLYELECTROLYTE HYDROGEL FORMULATIONS AND METHODS FOR MAKING AND USING THE SAMECROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of and priority to co-pending U.S. Provisional Patent Application No. 63 / 535,727, filed on August 31 , 2023, and 63 / 584,982, filed on September 25, 2023, the contents of which are incorporated by reference herein in their entireties.BACKGROUND

[0002] Vascular embolization is a common endovascular procedure that involves deploying an occlusive agent through a catheter to stop blood flow. Embolization is performed to treat a variety of conditions ranging from tumor devascularization to gastrointestinal bleeding to controlling benign hypertrophy of the prostate. These procedures are typically performed under fluoroscopic guidance and radiopaque markers on the guidewires and catheters give feedback to the physician navigating to the target site. Many embolic agents are currently available for these applications but have drawbacks including the use of harmful solvents, undesirable polymerization that can entrap catheters and guidewires, and a lack of visibility during deployment that can lead to off target embolization.SUMMARY

[0003] Described herein are polyelectrolyte (PE) hydrogels that have properties suited for numerous medical applications. The polyelectrolyte hydrogels are composed of a mixture of one or more water soluble polycationic polyelectrolytes, one or more water soluble polyanionic polyelectrolytes, and monovalent and / or divalent ions. Depending on the selection and the amount of polycationic polyelectrolyte, the polyanionic polyelectrolyte, monovalent and / or divalent ions, charge ratio, and inclusion of any additional additives or components, the mechanical properties, durability, deliverability, size of vessel occluded, and clotting efficacy can be adjusted to fit the intended application. The PE hydrogels remain dimensionally stable and insoluble in physiological conditions.

[0004] Other systems, methods, features, and advantages of the present disclosure will be or become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the present disclosure, andbe protected by the accompanying claims. In addition, all optional and preferred features and modifications of the described embodiments are usable in all aspects of the disclosure taught herein. Furthermore, the individual features of the dependent claims, as well as all optional and preferred features and modifications of the described embodiments are combinable and interchangeable with one another.BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Many aspects of the present disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present disclosure. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.

[0006] FIGS. 1 A-1 D show the characterization of the effect of charge ratio on the performance of PE hydrogels comprised of protamine sulfate and xanthan gum. The percent weight of PE hydrogels is fixed at 5% and the added salt molarity is fixed to 1 molar. (A) Viscosity curves as a function of shear rate for 1:4, 1 :1 , and 2:1 positive to negative charge ratios. (B) Injection force through 0.0235“ inner diameter with 130 cm length catheter as a function of charge ratio. (C) Temperature stability of the elastic modulus (G1) for variation in charge ratio. (D) Recovery of the elastic modulus (G') after repeated deformation to 100% for 1 :4 charge ratio and 2:1 charge ratio. Samples were subjected to 100% strain for 1 minute and after a 6 second relaxation period a 1% strain was applied for 1 minute and the elastic modulus (G1) and loss modulus (G") measured.

[0007] FIGS. 2A-2D show the characterization of the effect of added sodium chloride molarity on the performance of PE hydrogels comprised of protamine sulfate and xanthan gum. The percent weight of PE solids is fixed at 5% and the charge ratio fixed at 1:1. (A) Viscosity curves as a function of shear rate 0.5 molar, 1.0 molar, and 1.5 molar added sodium chloride formulations with 5% weight PE solids. (B) Injection force through 0.0235“ inner diameter with 130 cm length catheter as a function of sodium chloride molarity with 5% weight PE solids. (2C) Temperature stability of the elastic modulus (G1) for 0.5 molar, 1.0 molar, and 1.5 molar added sodium chloride formulations at 5% weight PE solids. (D) Recovery of the elastic modulus (G1) after repeated deformation to 100% for 0.5 molar and 1.0 molar formulations of 9% polyelectrolyte concentration. Samples were subjected to 100% strain for 1 minute and after a 6 second relaxation period a 1% strain was applied for 1 minute and the elastic modulus (G1) and loss modulus (G") measured.

[0008] FIG. 3 shows (A) 0.5 molar added sodium chloride PE hydrogel with 5% PE solids of protamine sulfate and xanthan at a 1 :1 charge ratio forms an opaque white freestanding gel; (B) 1.0 molar added sodium chloride PE hydrogel with 5% PE solids of protamine sulfate and xanthan at a 1 :1 charge ratio forms a translucent freestanding gel; and (C) 1.5 molar added sodium chloride PE hydrogel with 5% PE solids of protamine sulfate and xanthan at a 1:1 charge ratio forms a transparent freestanding gel. The total sodium concentration from added sodium chloride and counterions in xanthan gum is estimated to be about 0.56, 1.06, and 1.56 respectively.

[0009] FIGS. 4A-4D show the characterization of the effect of the percent solids on the performance of PE hydrogels comprised of protamine sulfate and xanthan gum. The molarity of added sodium chloride is fixed to 1 molar and the charge ratio fixed at 1 :1. (A) Viscosity curves as a function of shear rate for 5 percent and 9 weight PE percent solids formulations. (B) Injection force through 0.0235“ inner diameter with 130 cm length catheter as a function of percent solids content. (C) Temperature stability of the elastic modulus (G1) for 5, 7.5 and 9 percent weight PE solids formulations. (D) Recovery of the elastic modulus (G') after repeated deformation to 100% for 5 percent and 9 percent solids formulations. Samples were subjected to 100% strain for 1 minute and after a 6 second relaxation period a 1% strain was applied for 1 minute and the elastic modulus (G1) and loss modulus (G") measured.

[0010] FIGS. 5A-5D show the characterization of the effect of added sodium chloride molarity on the performance of PE hydrogels comprised of poly(guanidinyl-propyl-methacrylamide) pGPMA and xanthan gum. The percent weight PE solids is fixed to 5% and the charge ratio fixed at 1 :1. (A) Viscosity curves as a function of shear rate 1.0 molar, and 1.5 molar added sodium chloride formulations. (B) Injection force through 0.027“ inner diameter with 130 cm length catheter as a function of sodium chloride molarity. (C) Temperature stability of the elastic modulus (G1) for 1.0 molar, and 1.5 molar added sodium chloride formulations. (D) Recovery of the elastic modulus (G1) after repeated deformation to 100% for 1.0 molar and 1.5 molar formulations. Samples were subjected to 100% strain for 1 minute and after a 6 second relaxation period a 1 % strain was applied for 1 minute and the elastic modulus (G1) and loss modulus (G") measured.

[0011] FIGS. 6A-6D show the characterization of the effect of the percent solids on the performance of PE hydrogels comprised of pGPMA and xanthan gum. The molarity of added sodium chloride is fixed to 1 molar and the charge ratio fixed at 1:1. (A) Viscosity curves as a function of shear rate for 5, 7, and 12 percent solids formulations. (B) Injection force through 0.027“ inner diameter with 130 cm length catheter as a function of percent solids content. (C)Temperature stability of the elastic modulus (G1) for 5, 7, and 12 percent solids formulations. (D) Recovery of the elastic modulus (G1) after repeated deformation to 100% for 5 percent and 9 percent PE solids formulations. Samples were subjected to 100% strain for 1 minute and after a 6 second relaxation period a 1% strain was applied for 1 minute and the elastic modulus (G1) and loss modulus (G") measured.

[0012] FIGS. 7A-7D show the characterization of the effect of adding fibers made from crosslinked gelatin on the performance of PE hydrogels comprised of protamine sulfate and xanthan gum. The percent weight of solids is fixed to 7%, added sodium chloride fixed to 0.5 molar, and the charge ratio fixed at 1 :1. (A) Viscosity curves as a function of shear rate for 0%, 1%, and 2% fiber content formulations. (B) Injection force through 0.0235“ inner diameter with 130 cm length catheter as a function of fiber content. (C) Temperature stability of the elastic modulus (G1) for 0%, 1%, and 2% fiber content formulations. (D) Recovery of the elastic modulus (G1) after repeated deformation to 100% for 1 % and 2% fiber content formulations. Samples were subjected to 100% strain for 1 minute and after a 6 second relaxation period a 1 % strain was applied for 1 minute and the elastic modulus (G1) and loss modulus (G") measured.

[0013] FIG. 8 shows the image of fibers made from crosslinked gelatin under backlight at 100x magnification.

[0014] FIGS. 9A-9B show the (A) PE hydrogel comprised of protamine and xanthan at a 1 :1 charge ratio, 0.5 molar added sodium chloride, and 7% solids with 25% tantalum added for radiopacity deployed in balanced salt solution through an 0.0235” catheter and (B) PE hydrogel comprised of protamine and xanthan at a 1 :1 ratio, 0.5 molar added sodium chloride, and 7% solids with iohexol at a concentration of 200 mg of Iodine per ml_ added for radiopacity deployed in balanced salt solution through an 0.027” catheter. In this example, the PE hydrogels hold the shape of the catheter through which they were injected and form stable coils that can occlude vessels.

[0015] FIGS. 10A-10D show the characterization of the effect of radiopaque contrast agents on the performance of PE hydrogels comprised of protamine sulfate and xanthan gum. The percent weight PE solids is fixed to 7% and the added salt molarity is fixed to 0.5 molar. (A) Viscosity curves as a function of shear rate for 200mgl / mL iohexol and 25% Tantalum. (B) Injection force through 0.027“ inner diameter with 130 cm length catheter for 200 mgl / mL iohexol and 25% tantalum. (C) Temperature stability of the elastic modulus (G1) for 200 mgl / mL iohexol and 25% tantalum. (D) Recovery of the elastic modulus (G1) after repeated deformation to 100% for 200mgl / mL iohexol and 25% tantalum. Samples were subjected to 100% strain for 1 minute and after a 6 second relaxation period a 1% strain was applied for 1 minute and the elastic modulus (G1) and loss modulus (G") measured.

[0016] FIG. 11 shows the in vitro characterization of occlusion efficacy of PE hydrogels comprised of protamine sulfate and xanthan with 25% tantalum by weight or 200 mgl / mL iohexol added for radiopacity. Both PE hydrogels were 7% weight PE solids, 0.5 molar added sodium chloride, and 1 : 1 charge ratio. The pressure at which the embolic formulations were able to hold a given tapered vessel diameter for greater than 5 minutes is shown in FIG 11. The liquid used in the in vitro model was a heparinized balanced salt solution to simulate the ionic and chemical conditions with no clotting factors as a worst-case test of the mechanical ability of the PE hydrogels to create an occlusion.

[0017] FIGS. 12A-12B show (A) pre-deployment angiogram in domestic swine with contrast agent showing the kidney anatomy prior to injection of embolic PE hydrogel and (B) injection of embolic PE hydrogel created a proximal plug in the cranial pole of the swine kidney. The tantalum in the PE hydrogel provides visibility without obscuring the catheter tip. No adhesion to the catheter was observed despite some reflux in this deployment.

[0018] FIG. 13A shows a volume of O.15mL+ / -.O25 mL of embolic PE hydrogel was injected into a gelatin mold made inside a 3mL syringe. The gelatin allows for the exchange of soluble compounds in a manner that imitates diffusion across vessel walls and through the embolic material in vivo. FIG. 13B shows the rate of iohexol dissipation from an embolic PE hydrogel comprising 7% PE solids of protamine and xanthan in a 1:1 charge ratio with 0.75 molar added sodium chloride was measured using UV-Vis spectroscopy. The intensity of the absorption peak at 245 nm was correlated with the percent dissipation of iohexol from the PE hydrogel over time. The starting concentration of iohexol in the PE hydrogel was 200 mgl / mL which is within the range of the concentration of contrast used in peripheral vascular procedures. After 5 minutes the PE hydrogel will be faintly visible and after 20 minutes it will be mostly invisible. This gradual fading of contrast allows the PE hydrogel to be highly visible when deployed, unlike embolic particles or gelatin commonly used today, but it will not create an artifact in future CT images like liquids or coils containing tantalum or platinum.

[0019] FIG. 14A shows the viscosity of a 9% solids polyelectrolyte concentration at a 1.5:1 positive to negative charge ratio for a hyaluronic acid-protamine polyelectrolyte PE hydrogel with 0 molar added sodium chloride. The decrease in viscosity with increasing shear rate shows theviability of this combination for catheter delivery. FIG. 14B shows the elastic modulus G’ of the same hyaluronic acid - protamine PE hydrogel recovers after multiple series of 100% strain.

[0020] FIG. 15 shows the coiling behavior and shape memory of the gel. When embolic PE hydrogel material was deployed in simulated use conditions, it displayed the ability to naturally coil and fill a larger vessel when flow slowed due to downstream occlusion. Over time, the coiled material compacted to form an occlusion with much higher packing density than can be achieved with typical embolization coils making successful occlusion independent of clot formation.

[0021] FIG. 16 shows the filling of the left atrial appendage with a polyelectrolyte hydrogel described herein.

[0022] FIGS. 17A-17D show the effect of adding salt (potassium chloride) up to the necessary level to ionically shield a PE hydrogel comprising 4.5% XG with 4.0% Chitosan HCI. The top row shows the PE hydrogel under a backlight with the concentration of potassium chloride in mg / mL. The lower row shows the gels under toplight with the corresponding molarity of added potassium chloride. (A) A viscous colloidal liquid with a non-homogeneous distribution of small particles of ionically bonded components forms at low salt concentrations. (B) A semi-solid gel that is able to hold its shape begins to form but the backlight image shows that it is still non-homogeneous. (C) A nearly homogeneous gel has formed. Adding more salt at this point serves to ensure no phase separation and increase the moduli of xanthan gum. (D) Shows the transparent nature of the XG- CS hydrogel at full ionic shielding after autoclave. After autoclave, a slight amber color change is noted.

[0023] FIGS. 18A-18C demonstrate the property of insolubility of XG-CS PE hydrogels contrasted with xanthan gum alone. (A) Left to right- 3:1 charge ratio XG-CS 1.0M NaCI opaque white PE hydrogel, 3:1 charge ratio XG-CS 0.36M CaCI2 clear PE hydrogel, 4% xanthan gum clear hydrogel, in petri dish on black background for contrast; (B) PE hydrogels and XG alone on white background prior to addition of BSS. (C) 2 min after adding a balanced salt solution to the petri dish, the xanthan gum gel has nearly dissolved away while the chitosan-salt-xanthan gum PE hydrogels remain insoluble. This is a crucial characteristic of the gels - that they shear thin, recover, and remain insoluble through electrostatic interactions in physiological conditions.

[0024] FIGS. 19A-19F show the effect of salt type, concentration, and temperature on the solubility of chitosan hydrochloride (4.0%, pH 5.1). (A) Backlit image at 23 °C 1 hour after initial dissolution of salts. Salt type by row and the salt concentration in mg / mL by column are indicated. The opaque images indicate insolubility of chitosan hydrochloride. (B) Same as (A) after 10 minin freezer at -20 °C (C) Backlit images in the same order as above at 23 °C and after 10 minutes at -20 °C with a fixed total charge molarity of 0.85M. (D) Absorbance data at 600nm for the plate displayed in FIG 19A. Higher absorbance indicates more salt out of chitosan. (E) Absorbance at 600nm for the plate displayed in FIG 19B. (F) Absorbance data corresponding to the images in FIG 19C.

[0025] FIGS. 20A-20D show the results of zeta potential measurements for carboxymethyl chitosan (CMC) at pH 7.1, 4% chitosan hydrochloride with no added salt (GO), and 4% chitosan hydrochloride with 0.85M and 0.45M added potassium chloride at pH 5.1. (A) zeta potential measurements. (B) Conductivity measurements. (C) Transmittance measurements. Shows that at 0.85M, loss of solubility and higher salt molarity contribute to the lower zeta potential in (A). The 0.45M sample does not appear to have lost any solubility and the decrease in zeta potential in (A) is likely due to thinning of the interfacial double layer from the ions in the salt.

[0026] FIGS. 21A-21 B show the operating ranges for each chloride salt for PE hydrogels comprising chitosan and xanthan gum. (A) Operating ranges in terms of total charge molarity which is the same as the total chloride ion molarity to normalize for the divalent cation salts. The gel point is the minimum amount of salt necessary to ionically shield the polyelectrolytes and constitutes the lower bound or minimum amount of salt to form a PE hydrogel. The maximum amount of salt is governed by the solubility of chitosan and the solid lines indicate full solubility at room temperature with dotted lines indicating where loss of solubility occurs and eventually the concentration at which the PE hydrogel will no longer retain the ideal properties for use as an embolic. Ideal operating ranges indicated by the dashed circles. (B) Same data as (A) represented in terms of concentration in mg / mL.

[0027] FIGS. 22A-22D show the effect of polyelectrolyte concentration on the behavior of XG-CS PE hydrogels made with a fixed concentration of 0.27M added CaCL and pH 5.80-5.95. The concentrations are indicated in mg / mL where XG50, indicates a xanthan gum concentration of 50mg / mL. (A) stepped flow viscosity curve showing the peak viscosity and shear thinning behavior of the PE hydrogels. (B) Viscosity range at a shear rate of 100s-1for 1 minute. (C) Initial elastic modulus (G’) at 1% strain, 1 Hz frequency, and the recovered elastic modulus after 100% strain, 1 Hz frequency for 1 minute. (D) Ratio of recovered G’ to shear thinned viscosity at 100s-1. A higher number is desirable and gives a sense of the initial strength of the embolic when it exits the delivery conduit versus the force to inject through a delivery conduit such as a catheter.

[0028] FIGS. 23A-23F CS-XG polyelectrolyte hydrogels with varied charge ratio Left: 2:3 Charge Ratio (CR), Middle: 1 :2 Charge Ratio, Right 1 :1 Charge Ratio. (A) PE hydrogels delivered into base of glass petri dish. (B) 30 seconds after balanced salt solution (BSS) added to petri dish. (C) 5 minutes after BSS added. The 1 :1 CR is noticeably more opaque. (D) 30 minutes after BSS added. (E) 24hrs after BSS added. The 1 :2 charge ratio sample has swollen noticeably and is breaking apart. (F) 24hrs after BSS added with backlight.

[0029] FIGS. 24A-24C demonstrate the ability of CS-XG PE hydrogels, with a varied range of polyelectrolyte concentration and salt types, to continue to strengthen in physiological media. All measurements shown were taken on samples prepared by letting the PE hydrogel sit in BSS for 30 minutes prior to measuring per the description in the methods section (A) Peak viscosity from stepped flow test. (B) Elastic modulus at 1% strain with 1Hz frequency. (C) Yield stress curves with the point considered the yield point enlarged for emphasis.

[0030] FIGS. 25A-B show flow model testing results and model detail. (A) shows the pressure held by exemplary formulations for three different end vessel diameters. (B) shows an example of the flow model used where the end vessel could be as large as 500 pm or taper down as low as 100 pm. “1” is where a hemostasis valve was connected and the catheter was advanced into the model. “2” connection to peristaltic pump “3” outflow bypass channel to control spikes in pressure during embolization “4a-4c” outflow channels that returned BSS to the pump reservoir through a filter to catch any embolic material that passed through the end channels. Deliveries were performed from the point labeled “D” for distal, or “P” for proximal to assess the behavior of the PE hydrogels under different flow conditions.

[0031] FIGS. 26A-C demonstrate use of a PE hydrogel pledget using a CS-XG formulation consisting of 4.0% chitosan HCI, 4.5% xanthan gum, 32.5% tantalum, 1.0% gelatin fibers, and 0.27M CaCL with pH 5.70. (A) shows how a 0.10mL PE pledget is cleanly pushed with sterile saline into the catheter lumen without leaving residue in the hub (Merit Maestro, 2.4Fr, 150cm microcatheter). (B) shows exemplary injection force curves for three different injection rates for 0.1 OmL PE pledgets (C) shows behavior in a flow model. The pledget exited the catheter in a coil shape and quickly compacted to form the occlusion shown at a flow rate of 160mL / min with a mean arterial pressure of lOOmmHg (+ / -6mmHg). After delivery, the pressure was ramped to 37kPa (277mmHg) and the extent of distal penetration into the model quantified.

[0032] FIGS. 27A-F shows an example of a delivery system for delivering the PE hydrogels in a pledget form described herein.Additional advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or can be learned by practice of the invention. The advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.DETAILED DESCRIPTION

[0033] Many modifications and other embodiments disclosed herein will come to mind to one skilled in the art to which the disclosed compositions and methods pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the disclosures are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. The skilled artisan will recognize many variants and adaptations of the aspects described herein. These variants and adaptations are intended to be included in the teachings of this disclosure and to be encompassed by the claims herein.

[0034] Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

[0035] As will be apparent to those of skill in the art upon reading this disclosure, each of the individual embodiments described and illustrated herein has discrete components and features which may be readily separated from or combined with the features of any of the other several embodiments without departing from the scope or spirit of the present disclosure.

[0036] Any recited method can be carried out in the order of events recited or in any other order that is logically possible. That is, unless otherwise expressly stated, it is in no way intended that any method or aspect set forth herein be construed as requiring that its steps be performed in a specific order. Accordingly, where a method claim does not specifically state in the claims or descriptions that the steps are to be limited to a specific order, it is no way intended that an order be inferred, in any respect. This holds for any possible non-express basis for interpretation, including matters of logic with respect to arrangement of steps or operational flow, plain meaning derived from grammatical organization or punctuation, or the number or type of aspects described in the specification.

[0037] All publications mentioned herein are incorporated herein by reference to disclose and describe the methods and / or materials in connection with which the publications are cited. The publications discussed herein are provided solely for their disclosure prior to the filing date of the present application. Nothing herein is to be construed as an admission that the present invention is not entitled to antedate such publication by virtue of prior invention. Further, the dates of publication provided herein can be different from the actual publication dates, which can require independent confirmation.

[0038] While aspects of the present disclosure can be described and claimed in a particular statutory class, such as the system statutory class, this is for convenience only and one of skill in the art will understand that each aspect of the present disclosure can be described and claimed in any statutory class.

[0039] It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the disclosed compositions and methods belong. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the specification and relevant art and should not be interpreted in an idealized or overly formal sense unless expressly defined herein.

[0040] Prior to describing the various aspects of the present disclosure, the following definitions are provided and should be used unless otherwise indicated. Additional terms may be defined elsewhere in the present disclosure.Definitions

[0041] As used herein, “comprising” is to be interpreted as specifying the presence of the stated features, integers, steps, or components as referred to, but does not preclude the presence or addition of one or more features, integers, steps, or components, or groups thereof. Moreover, each of the terms “by”, “comprising,” “comprises”, “comprised of,” “including,” “includes,” “included,” “involving,” “involves,” “involved,” and “such as” are used in their open, non-limiting sense and may be used interchangeably. Further, the term “comprising” is intended to include examples and aspects encompassed by the terms “consisting essentially of” and “consisting of.” Similarly, the term “consisting essentially of” is intended to include examples encompassed by the term “consisting of.

[0042] As used in the specification and the appended claims, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “an excipient” include, but are not limited to, mixtures or combinations of two or more such excipients, and the like.

[0043] It should be noted that ratios, concentrations, amounts, and other numerical data can be expressed herein in a range format. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint. It is also understood that there are a number of values disclosed herein, and that each value is also herein disclosed as “about” that particular value in addition to the value itself. For example, if the value “10” is disclosed, then “about 10” is also disclosed. Ranges can be expressed herein as from “about” one particular value, and / or to “about” another particular value. Similarly, when values are expressed as approximations, by use of the antecedent “about,” it will be understood that the particular value forms a further aspect. For example, if the value “about 10” is disclosed, then “10” is also disclosed.

[0044] When a range is expressed, a further aspect includes from the one particular value and / or to the other particular value. For example, where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included in the disclosure, e.g. the phrase “x to y” includes the range from ‘x’ to ‘y’ as well as the range greater than ‘x’ and less than ‘y’. The range can also be expressed as an upper limit, e.g. ‘about x, y, z, or less’ and should be interpreted to include the specific ranges of ‘about x’, ‘about y’, and ‘about z’ as well as the ranges of ‘less than x’, less than y’, and ‘less than z’. Likewise, the phrase ‘about x, y, z, or greater’ should be interpreted to include the specific ranges of ‘about x’, ‘about y’, and ‘about z’ as well as the ranges of ‘greater than x’, greater than y’, and ‘greater than z’. In addition, the phrase “about ‘x’ to ‘y’”, where ‘x’ and ‘y’ are numerical values, includes “about ‘x’ to about ‘y’”.

[0045] It is to be understood that such a range format is used for convenience and brevity, and thus, should be interpreted in a flexible manner to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or subranges encompassed within that range as if each numerical value and sub-range is explicitly recited. To illustrate, a numerical range of “about 0.1 % to 5%” should be interpreted to include not only the explicitly recited values of about 0.1% to about 5%, but also include individual values (e.g., about 1%, about 2%, about 3%, and about 4%) and the sub-ranges (e.g., about 0.5% to about 1.1%; about 5% to about 2.4%; about 0.5% to about 3.2%, and about 0.5% to about 4.4%,and other possible sub-ranges) within the indicated range. Thus, for example, if a component is in an amount of about 1%, 2%, 3%, 4%, or 5%, where any value can be a lower and upper endpoint of a range, then any range is contemplated between 1% and 5% (e.g., 1% to 3%, 2% to 4%, etc.).

[0046] As used herein, the terms “about,” “approximate,” “at or about,” and “substantially” mean that the amount or value in question can be the exact value or a value that provides equivalent results or effects as recited in the claims or taught herein. That is, it is understood that amounts, sizes, formulations, parameters, and other quantities and characteristics are not and need not be exact, but may be approximate and / or larger or smaller, as desired, reflecting tolerances, conversion factors, rounding off, measurement error and the like, and other factors known to those of skill in the art such that equivalent results or effects are obtained. In some circumstances, the value that provides equivalent results or effects cannot be reasonably determined. In such cases, it is generally understood, as used herein, that “about” and “at or about” mean the nominal value indicated ±10% variation unless otherwise indicated or inferred. In general, an amount, size, formulation, parameter or other quantity or characteristic is “about,” “approximate,” or “at or about” whether or not expressly stated to be such. It is understood that where “about,” “approximate,” or “at or about” is used before a quantitative value, the parameter also includes the specific quantitative value itself, unless specifically stated otherwise.

[0047] The term “alkyl group” as used herein is a branched or unbranched saturated hydrocarbon group of 1 to 25 carbon atoms, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, / -butyl, pentyl, hexyl, heptyl, octyl, decyl, tetradecyl, hexadecyl, eicosyl, tetracosyl, and the like. Examples of longer chain alkyl groups include, but are not limited to, a palmitate group. A “lower alkyl” group is an alkyl group containing from one to six carbon atoms.

[0048] The term “cycloalkyl group” as used herein is a non-aromatic carbon-based ring composed of at least three carbon atoms. Examples of cycloalkyl groups include, but are not limited to, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, etc.

[0049] The term “treat” as used herein is defined as maintaining or reducing the symptoms of a pre-existing condition when compared to the same symptoms in the absence of the adminsitration of a PE hydrogel described herein. The term “prevent” as used herein is the ability of the PE hydrogels described herein to completely eliminate the activity or reduce the activity when compared to the same activity in the absence of the gel. The term “inhibit” as used herein refers to the ability of the a PE hydrogel described herein to slow down or prevent a process.

[0050] “Subject” refers to mammals including, but not limited to, humans, non-human primates, sheep, dogs, rodents (e.g., mouse, rat, guinea pig, etc.), cats, rabbits, cows, horses, and nonmammals including vertebrates, birds, fish, amphibians, and reptiles.

[0051] The term “salt” as used herein is defined as a dry solid form of a water-soluble compound that possesses cations and anions. When the salt is added to water, the salt dissociates into cations and anions. A polycationic salt is a compound having a plurality of cationic groups with anionic counterions. A polyanionic salt is a compound having a plurality of anionic groups with cationic counterions.

[0052] The term “polyelectrolytes” as used herein is defined as polymers with ionizable functional groups, where the ionized functional groups can be incorporated in the polymer backbone, a sidechain of the polymer, or a combination thereof. Polycations and polyanions are produced when a polycationic salt or a polyanionic salt is dissolved in water.

[0053] The term “ionic” as used herein is defined as any charged element. For example, the ions can be positively charged species including monovalent cations (e.g., sodium or potassium) or divalent cations (e.g., calcium or magnesium). The ions can be negatively charged species including monovalent anions (e.g., chloride).

[0054] The term "molecular weight" is used herein to refer to the average molecular mass of an ensemble of synthetic polymers that contains a distribution of molecular masses. Unless otherwise noted, values reported herein are weight-average molecular weight (Mw).

[0055] The term "transient" as used herein with respect to the contrast agent is defined herein as the ability of the contrast agent to diffuse or escape over time from a PE hydrogel as described herein.

[0056] The term "temporary contrast" as used herein occurs when the majority of the transient contrast agent diffuses from a PE hydrogel described herein such that the transient contrast agent cannot be detected in the subject by imaging techniques such as, for example, fluoroscopy or CT.

[0057] “Physiological conditions” refers to conditions such as osmolality, ion concentrations, pH, temperature, etc. within a particular area of the subject. For example, the normal blood sodium concentration range is between 135 and 145 mMol / L in a human.

[0058] As used herein, a plurality (i.e., more than one) of items, structural elements, compositional elements, and / or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individuallyidentified as a separate and unique member. Thus, no individual member of any such list should be construed as a de facto equivalent of any other member of the same list based solely on its presentation in a common group, without indications to the contrary.

[0059] As used herein, the term “multimodal polymer’’ is a polymer with a molecular mass distribution curve being the sum of at least two or more molecular mass unimodal distribution curves. For example, polyanionic polyelectrolytes can be mixed to create a multimodal molecular weight distribution to tune the flow behavior of the polyelectrolyte hydrogel under shear.

[0060] As used herein, the term polyelectrolyte (PE) “hydrogel” is a composition of matter wherein the cohesion of the hydrogel is due to electrostatic interactions between oppositely charged polyelectrolytes, and wherein the elastic modulus is greater than the viscous modulus under no shear. The polyelectrolyte hydrogels are stable dimensionally and insoluble in water and physiological fluids.

[0061] Concentrations, amounts, and other numerical data may be expressed or presented herein in a range format. It is to be understood that such a range format is used merely for convenience and brevity and thus should be interpreted flexibly to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range was explicitly recited. As an example, a numerical range of “about 1” to “about 5” should be interpreted to include not only the explicitly recited values of about 1 to about 5, but also to include individual values and sub-ranges within the indicated range. Thus, included in this numerical range are individual values such as 2, 3, and 4, the sub-ranges such as from 1-3, from 2-4, from 3-5, from about 1 - about 3, from 1 to about 3, from about 1 to 3, etc., as well as 1, 2, 3, 4, and 5, individually. The same principle applies to ranges reciting only one numerical value as a minimum or maximum. Furthermore, such an interpretation should apply regardless of the breadth or range of the characters being described.

[0062] Disclosed are materials and components that can be used for, can be used in conjunction with, can be used in preparation for, or are products of the disclosed compositions and methods. These and other materials are disclosed herein, and it is understood that when combinations, subsets, interactions, groups, etc., of these materials are disclosed, that while specific reference of each various individual and collective combination and permutation of these compounds may not be explicitly disclosed, each is specifically contemplated and described herein. For example, if a class of molecules A, B, and C are disclosed, as well as a class of molecules D, E, and F, andan example of a combination A + D is disclosed, then even if each is not individually recited, each is individually and collectively contemplated. Thus, in this example, each of the combinations A + E, A + F, B + D, B + E, B + F, C + D, C + E, and C + F, are specifically contemplated and should be considered disclosed from disclosure of A, B, and C; D, E, and F; and the example combination of A + D. Likewise, any subset or combination of these is also specifically contemplated and disclosed. Thus, for example, the sub-group of A + E, B + F, and C + E is specifically contemplated and should be considered disclosed from disclosure of A, B, and C; D, E, and F; and the example combination of A + D. This concept applies to all aspects of this disclosure including, but not limited to, steps in methods of making and using the disclosed compositions. Thus, if there exist a variety of additional steps that can be performed with any specific embodiment or combination of embodiments of the disclosed methods, each such combination is specifically contemplated and should be considered disclosed.Polyelectrolyte Hydrogel Formulations

[0063] Described herein are polyelectrolyte (PE) hydrogels that have properties suited for delivery to a subject. The polyelectrolyte hydrogels are composed of a mixture of one or more water soluble polycationic polyelectrolytes, one or more water soluble polyanionic polyelectrolytes, and monovalent and / or divalent ions. Depending on the selection and the amount of polycationic polyelectrolyte, the polyanionic polyelectrolyte, monovalent and / or divalent ions charge ratio, and inclusion of any additional additives or components, the mechanical properties, durability, deliverability, and size of vessel occluded can be adjusted to fit the intended application.

[0064] The PE hydrogels remain stable and insoluble in physiological conditions. Typical hydrogels swell in water. The hydrogels described herein are dimensionally stable at physiological conditions. In one aspect, the hydrogel does not swell or shrink more than 10.0%, or from 0.1 %, 0.5 %, 1.0%, 2.0%, 3.0%, 4.0%, 5.0%, 6.0%, 7.0%, 8.0%, or 9.0% (or any range thereof such as 0.5 % to 9.0 %), when introduced into physiological conditions. Not wishing to be bound by theory, the stability of the hydrogels described herein is due to the electrostatic interactions between the polyanionic and polycationic polyelectrolytes.

[0065] In one aspect, the PE hydrogels exhibit a reversible decrease in elastic modulus and viscosity under shear flow during delivery through a conduit (e.g., a needle or catheter). The elastic modulus and viscosity of the PE hydro PE hydrogels decreases during delivery from the conduit and when the material exits the conduit at the target site, shear forces decrease and theelastic modulus and viscosity recover to near their initial values. The magnitude of the decrease and rebound in elastic modulus and viscosity can be adjusted by the selection of polyelectrolytes, the charge ratio between polyelectrolyte constituents, the polyelectrolyte concentration, the concentration of the monovalent and / or divalent ions, and the inclusion of additional components described herein.

[0066] In one aspect, the elastic modulus and the viscosity of the polyelectrolyte hydrogel continues to increase after delivery into physiological media (e.g., into a subject). In one aspect, the elastic modulus of the polyelectrolyte hydrogel after 30 minutes in physiological media is between 200 Pa and 25,000 Pa. In another aspect, the elastic modulus of the polyelectrolyte hydrogel after 30 minutes in physiological media is 200 Pa, 500 Pa, 1 ,000 Pa, 1,500 Pa, 2,000 Pa, 2,500 Pa, 3,000 Pa, 3,500 Pa, 4,000 Pa, 4,500 Pa, 5,000 Pa, 5,500 Pa, 6,000 Pa, 10,000 Pa, 15,000 Pa, 20,000 Pa, or 25,000 Pa, where any value can be a lower and upper endpoint of a range (e.g., 3,000 Pa to 8,000 Pa).

[0067] In another aspect, the elastic modulus of the polyelectrolyte hydrogel remains greater than the viscous modulus. In another aspect, the elastic modulus continues to increase after delivery into physiological media. In another aspect, the elastic modulus of the PE hydrogel after delivery into physiological media remains within ±10% of the initial elastic modulus prior to delivery.

[0068] In another aspect, the prior to delivery to the subject, the PE hydrogel can be exposed to an ionic liquid to modify one or more properties of the hydrogel. In one aspect, the polyelectrolyte hydrogel is exposed to a liquid with ionic content less than the polyelectrolyte hydrogel to increase the elastic modulus prior to delivery.

[0069] In another aspect, the viscosity of the polyelectrolyte hydrogel under shear decreases such that the injection force through a catheter is less than 20 Ibf, or is 2 Ibf, 4 Ibf, 6 Ibf, 8 Ibf, 10 Ibf, 12 Ibf, 14 Ibf, 16 Ibf, 18 Ibf, or 20 Ibf, where any value can be a lower and upper endpoint of a range (e.g., 4 Ibf to 12 Ibf).

[0070] Depending upon the selection and the amount of the polycationic and polyanionic polyelectrolytes, the shear thinning properties of the hydrogel can be modified. In one aspect, the polyanionic polyelectrolyte has from 10 mol% to 90 mol% ionized side chains above pH 4.5. In another aspect, the polyanion polyelectrolyte has only anionic charged groups, i.e. no cationic groups. In another aspect, the molecular weight of the polyanion is from about 20 kDa to about 10,000 kDa. In another aspect, the polyanion polyelectrolyte is linear or branched. In another aspect, the polyanionic polyelectrolyte comprises multiple molecular weight polymers to create amultimodal molecular weight distribution. Examples of suitable polyanionic polyelectrolytes are described in greater detail below.

[0071] In another aspect, the polycationic polyelectrolyte has from 85.0 mol% to 100 mol% ionized side chains below pH 6.3. In another aspect, the polycation polyelectrolyte has only cationic charged groups, i.e. no anionic groups. Examples of suitable polycationic polyelectrolytes are described in greater detail below.

[0072] When the polyelectrolytes are dissolved in water together, the oppositely charged sites are attracted to each other. Monovalent and / or divalent ions provide an ionic shield and prevent the polycation and polyanion from fully binding together. Monovalent and divalent ions each have advantages depending on the polyelectrolytes comprising the hydrogel. For example, the monovalent and / or divalent ions control the homogeneity of the PE hydrogel and itself can be used as a level to adjust the mechanical properties of the gel. The concentration of the added monovalent and / or divalent ions is chosen depending on the polyelectrolytes selected, the concentration of polyelectrolytes, and desired hydrogel characteristics.

[0073] In one aspect, the ions include monovalent cations (e.g., sodium and / or potassium) and monovalent anions (e.g., chloride) with a concentration from about 0.10 M to about 2.5M. In another aspect, the monovalent ions are sodium and chloride ions with a concentration from about 0.10 M, 0.25 M, 0.50 M, 0.75 M, 1.00 M, 1.25 M, 1.50 M, 1.75 M, 2.00 M, 2.25 M, or 2.5 M, where any value can be a lower and upper endpoint of a range (e.g., 0.50 M to 1.50 M).

[0074] In one aspect, the ions include divalent cations (e.g., calcium and / or magnesium) and monovalent anions (e.g., chloride) with a concentration from about 0.10 M to about 2.5M. In another aspect, the monovalent ions are sodium and chloride ions with a concentration from about 0.10 M, 0.25 M, 0.50 M, 0.75 M, 1.00 M, 1.25 M, 1.50 M, 1.75 M, 2.00 M, 2.25 M, or 2.5 M, where any value can be a lower and upper endpoint of a range (e.g., 0.50 M to 1.50 M).

[0075] In addition to the selection of the polyelectrolytes and monovalent and / or divalent ions, the charge ratio of the polyelectrolytes at a particular pH is another factor with respect to producing and modifying the properties of the hydrogels described herein. The charge density of each polyelectrolyte can be described as the mass per mol of charge. For example, in protamine sulfate (salmine), the arginine groups carry a positive charge and there are 21 arginine groups per protamine molecule. Using this information and the molecular weight, the mass per mol of charge can be calculated. For example, the molecular weight of salmine is 4236 Da and the mass per mol of positive charge is 201 .7 grams. Once the charge density for the polycation and polyanionare known, the charge ratio can be selected. In one aspect, the charge ratio between the polycationic and polyanionic polyelectrolytes at pH of about 4.5 to about 8 is from 6:1 to 1:6. In another aspect, the charge ratio is 1 :1 or about 1 :1 ; however, the ratio can be adjusted to modify the properties of the hydrogel.

[0076] Depending upon the selection and the amount of the polycationic and polyanionic polyelectrolytes, the initial elastic modulus of the PE hydrogel can be modified. In one aspect, the initial elastic modulus of the hydrogel is greater than or equal to 200 Pa and is at least twice as large as the viscous modulus.

[0077] The ability of the PE hydrogels to recover their elastic moduli after being administered to the subject makes the hydrogels useful in a number of medical applications such as, for example, embolic agents. In one aspect, the recovered elastic modulus of the polyelectrolyte hydrogel in physiological conditions is at least 80% of the initial elastic modulus of the polyelectrolyte hydrogel. In one aspect, the recovered elastic modulus of the polyelectrolyte hydrogel in physiological conditions is at least 80%, 85%, 90%, 95%, or 100% of the initial elastic modulus. In another aspect, the hydrogel has an elastic modulus in physiological conditions equal to or greater than the initial elastic modulus. In another aspect, the elastic modulus recovers to a sufficient level to provide occlusion or fill a void.

[0078] The percent weight of total solids in the hydrogel is selected based on the solubility of the polyelectrolytes and desired characteristics of the hydrogel, with a higher percent weight generally increasing the elastic modulus and viscosity. The mass of each component to be added is calculated based on the desired batch size and the selected polyelectrolyte concentration, charge ratio, and concentration of added monovalent and / or divalent ions. The total concentration of the monovalent and / or divalent ions in the PE hydrogel includes the counterions from the polyelectrolytes and the added monovalent and / or divalent ions.

[0079] Each component used to prepare the polyelectrolyte hydrogels and methods for making and using the same are described in detail below.Polycationic Polyelectrolytes

[0080] The polycationic polyelectrolyte is compound having a plurality of cationic groups or groups that can readily be converted to cationic groups by adjusting the pH. In one aspect, the polycationic polyelectrolyte is a polymer having a plurality of cationic groups and pharmaceutically-acceptable anionic counterions. In one aspect, the polycationic polyelectrolytehas from about 10 mol% to about 90 mol% cationic (i.e. , ionized side chains) above pH 6, or about 10 mol%, 20 mol%, 30 mol%, 40 mol%, 50 mol%, 60 mol%, 70 mol%, 80 mol%, or 90 mol%, where any value can be a lower and upper endpoint of a range (e.g., 30 mol% to 70 mol%). In another aspect, the polycation has only cationic charged groups, i.e. no anionic groups.

[0081] In one aspect, the polycationic polyelectrolyte is a polymer having a polymer backbone with a plurality of cationic groups and pharmaceutically-acceptable anionic counterions. The cationic groups can be pendant to the polymer backbone and / or incorporated within the polymer backbone.

[0082] In one aspect, the polycationic polyelectrolyte is derived by dissolving a polycationic salt in water. In one aspect, the polycationic salt is a polycationic hydrochloride salt, wherein upon mixing with water produces the polycationic polyelectrolyte and chloride ions. In another aspect, the polycationic salts described herein can be produced by combining a polymer with a plurality of basic groups (e.g., amino groups) with an acid to produce the corresponding cationic groups. In various aspects, acids which may be employed to form pharmaceutically acceptable polycationic salts include inorganic acids as hydrochloric acid, acetic acid, glutaric acid, or other monovalent carboxylic acids.

[0083] Also, basic nitrogen-containing groups can be quaternized with such agents as lower alkyl halides, such as methyl, ethyl, propyl, and butyl chloride, bromides, and iodides; dialkyl sulfates like dimethyl, diethyl, dibutyl, and diamyl sulfates, long chain halides such as decyl, lauryl, myristyl and stearyl chlorides, bromides and iodides, aralkyl halides like benzyl and phenethyl bromides, and others.

[0084] In other aspects, when the polycationic polyelectrolyte is a polymer, the polycation can be produced by the polymerization of one or more monomers, where the monomers possess one or more cationic groups with corresponding counterion. In one aspect, once the polycation has been prepared, excess ions can be removed from the polycation by filtration or dialysis prior to drying (e.g., lyophilization) to produce a polycationic salt with stoichiometric amounts of anionic counterions relative to the number of cationic groups.

[0085] In one aspect, the counterion of the polycationic polyelectrolyte is a monovalent ion such as, for example, chloride, pyruvate, acetate, tosylate, benzenesulfonate, benzoate, lactate, salicylate, glucuronate, galacturonate, nitrite, mesylate, trifluoroacetate, nitrate, gluconate, glycolate, formate, or any combination thereof. In one aspect, the counterion of the polycationic polyelectrolyte is a multivalent ion such as, for example, sulfate or phosphate.

[0086] In one aspect, the polycationic polyelectrolyte is a pharmaceutically-acceptable salt of a polyamine. The amino groups of the polyamine can be branched or part of the polymer backbone. In one aspect, the polyamine comprises two or more pendant amino groups, wherein the amino group comprises a primary amino group, a secondary amino group, tertiary amino group, a quaternary amine, an alkylamino group, a heteroaryl group, a guanidinyl group, an imidazolyl, or an aromatic group substituted with one or more amino groups.

[0087] In one aspect, the pharmaceutically-acceptable salt of the polyamine can include an aryl group having one or more amino groups directly or indirectly attached to the aromatic group. Alternatively, the amino group can be incorporated in the aromatic ring. For example, the aromatic amino group is a pyrrole, an isopyrrole, a pyrazole, imidazole, a triazole, or an indole. In another aspect, the aromatic amino group includes the isoimidazole group present in histidine. In another aspect, the biodegradable polyamine can be gelatin modified with ethylenediamine.

[0088] In general, the polyamine salt is a polymer with a large excess of positive charges relative to negative charge at or near physiological pH. For example, the polycation can have from 10 to 90 mole %, 10 to 80 mole %, 10 to 70 mole %, 10 to 60 mole %, 10 to 50 mole %, 10 to 40 mole %, 10 to 30 mole %, or 10 to 20 mole % protonated amino groups. In another aspect, all the amino groups of the polyamine are protonated.

[0089] In one aspect, the polycationic polyelectrolyte can have a protonated residue of lysine, histidine, or arginine. For example, arginine has a guanidinyl group, where the guanidinyl group is a suitable amino group that can be converted to a cationic group useful herein.

[0090] In another aspect, the polyamine can be a biodegradable synthetic polymer or naturally- occurring polymer. The mechanism by which the polyamine can degrade will vary depending upon the polyamine that is used. In the case of natural polymers, they are biodegradable because there are enzymes that can hydrolyze the polymer chain. For example, proteases can hydrolyze natural proteins like gelatin. In the case of synthetic biodegradable polyamines, they also possess chemically labile bonds. For example, aminoesters have hydrolyzable ester groups.

[0091] In one aspect, the polyamine includes a polysaccharide, a protein, peptide, or a synthetic polyamine. Polysaccharides bearing two or more amino groups can be used herein. In one aspect, the polysaccharide is a natural polysaccharide such as chitosan or chemically modified chitosan. Similarly, the protein can be a synthetic or naturally-occurring compound. In another aspect, the polyamine is a synthetic polyamine such as poly(aminoesters), polyester amines, poly(disulfide amines), mixed poly(ester and amide amines), and peptide crosslinked polyamines.

[0092] In one aspect, the polycation is a chemically modified chitosan. Chitosan possesses hemostatic, mucoadhesive, and endothelial adhesive properties, all of which are useful in embolic polyelectrolyte hydrogels. Not wishing to be bound by theory, when paired with a suitable anionic polysaccharide, chitosan exhibits hydrogen bonding and polymer chain entanglement in addition to the electrostatic interactions described herein. This synergistic layering of interactions makes polyelectrolyte hydrogels prepared from chitosan more cohesive and capable of occluding larger vessels when the hydrogel is used as an embolic.

[0093] In one aspect, the chemically modified chitosan increases the solubility of the chitosan and retains only positive charge. In one aspect, the modified chitosan is a pharmaceutically acceptable salt of chitosan. Examples of pharmaceutically acceptable salt of chitosan include, but are not limited to, chloride, glutamate, or acetate. In one aspect, the modified chitosan carries only a positive charge. For example, the modified chitosan does not include any negative or zwitterionic charge(s) throughout the chitosan polymer.

[0094] In one aspect, the pharmaceutically acceptable salt of chitosan has a degree of deacetylation (DDA) greater than 85%. In another aspect, the pharmaceutically acceptable salt of chitosan has a degree of deacetylation (DDA) of 85%, 90%, 95%, 99%, 99.9%, or 100%, where any value can be a lower and upper endpoint of a range (e g., 90% to 95%). Not wishing to be bound by theory, if the degree of deacetylation is less than 85%, the pharmaceutically acceptable salt of chitosan is less soluble and prone to crashing out of solution as well as having reducing gel strength in physiological media due to the lower charge density.

[0095] In one aspect, the pharmaceutically acceptable salt of chitosan has an average molecular weight between 10 kDa and 130 kDa. In another aspect, the pharmaceutically acceptable salt of chitosan has an average molecular weight between 10 kDa, 20 kDa, 30 kDa, 40 kDa, 50 kDa, 60 kDa, 70 kDa, 80 kDa, 90 kDa, 100 kDa, 110 kDa, 120 kDa or 130 kDa, where any value can be a lower and upper endpoint of a range (e.g., 20 kDa to 50 kDa). Not wishing to be bound by theory, if the molecular weight is less than 10 kDa, the chitosan does not have a sufficient interaction to make the hydrogel remain cohesive in flowing blood conditions. If the molecular weight is greater than 130 kDa, the material is too viscous and uninjectable.

[0096] In one aspect, the pharmaceutically acceptable salt of chitosan is from about 0.70 weight percent to about 8 weight percent of the hydrogel. In another aspect, the pharmaceutically acceptable salt of chitosan is 0.7 weight percent, 1.0 weight percent, 1.5 weight percent, 2.0 weight percent, 2.5 weight percent, 3.0 weight percent, 3.5 weight percent, 4.0 weight percent,4.5 weight percent, 5.0 weight percent, 5.5 weight percent, 6.0 weight percent, 6.5 weight percent, 7.0 weight percent, 7.5 weight percent, or 8.0 weight percent of the hydrogel, where any value can be a lower and upper endpoint of a range (e.g., 0.7 weight percent to 3.5 weight percent). Not wishing to be bound by theory, if the concentration of the pharmaceutically acceptable salt of chitosan is too low, there is insufficient charge to create an insoluble hydrogel. If the concentration is too high, the viscosity of the hydrogel is too high and limits the use of the hydrogel.

[0097] In one aspect, when the pharmaceutically acceptable salt of chitosan is used to produce the PE hydrogel, the hydrogel has a pH from 4.5 to 6.3. In another aspect, when the pharmaceutically acceptable salt of chitosan is used to produce the PE hydrogel, the hydrogel has a pH of hydrogel is 4.5, 4.75, 5.0, 5.25, 5.5, 5.75, 6.0, 6.25, or 6.3, where any value can be a lower and upper endpoint of a range (e.g., 4.75 to 6.0).

[0098] In one aspect, the pharmaceutically-acceptable salt of the polyamine can be an amine- modified natural polymer. For example, the amine-modified natural polymer can be gelatin modified with one or more alkylamino groups, heteroaryl groups, or an aromatic group substituted with one or more amino groups. Examples of alkylamino groups are depicted in Formulae IV-VIR 13(CH2)tN(CH2)uNR17R18V R16'NR13(CH2)VN-{(CH2)WN}A'(CH2)XNR21R22VI R19 R20 wherein R13-R22are, independently, hydrogen, an alkyl group, or a nitrogen containing substituent; s, t, u, v, w, and x are an integer from 1 to 10; andA is an integer from 1 to 50, where the alkylamino group is covalently attached to the natural polymer. In one aspect, if the natural polymer has a carboxyl group (e.g., acid or ester), the carboxyl group can be reacted with an alkyldiamino compound to produce an amide bond and incorporate the alkylamino group into the polymer. Thus, referring to formulae IV-VI, the amino group NR13is covalently attached to the carbonyl group of the natural polymer.

[0099] As shown in formula IV-VI, the number of amino groups can vary. In one aspect, the alkylamino group is-NHCH2NH2, -NHCH2CH2NH2, -NHCH2CH2CH2NH2, -NHCH2CH2CH2CH2NH2,-NHCH2CH2CH2CH2CH2NH2,-NHCH2NHCH2CH2CH2NH2,-NHCH2CH2NHCH2CH2CH2NH2,-NHCH2CH2CH2NHCH2CH2CH2CH2NHCH2CH2CH2NH2,-NHCH2CH2NHCH2CH2CH2CH2NH2,-NHCH2CH2NHCH2CH2CH2NHCH2CH2CH2NH2, or-NHCH2CH2NH(CH2CH2NH)dCH2CH2NH2, where d is from 0 to 50.

[0100] In one aspect, the pharmaceutically-acceptable salt of the amine-modified natural polymer can include an aryl group having one or more amino groups directly or indirectly attached to the aromatic group. Alternatively, the amino group can be incorporated in the aromatic ring. For example, the aromatic amino group is a pyrrole, an isopyrrole, a pyrazole, imidazole, a triazole, or an indole. In another aspect, the aromatic amino group includes the isoimidazole group present in histidine. In another aspect, the biodegradable polyamine can be gelatin modified with ethylenediamine.

[0101] In other aspects, the polycationic polyelectrolyte can be a dendrimer. The dendrimer can be a branched polymer, a multi-armed polymer, a star polymer, and the like. In one aspect, the dendrimer is a polyalkylimine dendrimer, a mixed amino / ether dendrimer, a mixed amino / amide dendrimer, or an amino acid dendrimer. In another aspect, the dendrimer is poly(amidoamine), or PAMAM. In one aspect, the dendrimer has 3 to 20 arms, wherein each arm comprises an amino group.

[0102] In one aspect, the polycationic polyelectrolyte includes a polyacrylate having one or more pendant protonated amino groups. For example, the backbone of the polycationic salt can be derived from the polymerization of acrylate monomers including, but not limited to, acrylates, methacrylates, acrylamides, methacrylamides, and the like. In one aspect, the polycationic salt backbone is derived from polyacrylamide. In other aspects, the polycationic salt is a random copolymer. In other aspects, the polycation is a block copolymer, where segments or portions ofthe co-polymer possess cationic groups or neutral groups depending upon the selection of the monomers and method used to produce the co-polymer.

[0103] In another aspect, the polycationic polyelectrolyte can be polyethyleneimine hydrochloride (linear or branched), cationically modified gelatin, cationic guar gum (hydroxypropyltrimonium chloride), poly-L-Lysine, poly(amidoamine), cationically modified polyvinylpyrrolidone derivatives, and cationically-modified poly(N-isopropylacrylamide), cationic polysaccharides, and cationically- modified polysaccharides.

[0104] In another aspect, the polycationic polyelectrolyte is a pharmaceutically-acceptable salt of a protamine. Protamines are polycationic, arginine-rich proteins that play a role in condensation of chromatin into the sperm head during spermatogenesis. As by-products of the fishing industry, commercially available protamines, purified from fish sperm, are readily available in large quantity and are relatively inexpensive. A non-limiting example of a protamine useful herein is salmine. In another aspect, the protamine is clupein.

[0105] In one aspect, protamine is from about 0.5 weight percent to about 15 weight percent of the hydrogel. In another aspect, protamine is 0.5 weight percent, 1.0 weight percent, 2.0 weight percent, 3.0 weight percent, 4.0 weight percent, 5.0 weight percent, 6.0 weight percent, 7.0 weight percent, 8.0 weight percent, 9.0 weight percent, 10.0 weight percent, 11.0 weight percent, 12.0 weight percent, 13.0 weight percent, 14.0 weight percent, or 15.0 weight percent of the hydrogel, where any value can be a lower and upper endpoint of a range (e.g., 3.0 weight percent to 8.0 weight percent).

[0106] In one aspect, the polycationic polyelectrolyte is a polymer with a plurality of guanidinyl groups. In one aspect, the guanidinyl groups are pendant to the polymer backbone. The number of guanidinyl groups present on the polycation ultimately determines the charge density of the polycation. In one aspect, the guanidinyl group can be derived from a residue of arginine attached to a polymer backbone.

[0107] The polyguanidinyl polymer can be a homopolymer or copolymer having a plurality of guanidinyl groups. In one aspect, the polyguanidinyl copolymer is a synthetic compound prepared by the free radical polymerization between a monomer such as an acrylate, a methacrylate, an acrylamide, a methacrylamide, or any combination thereof, and a guanidinyl monomer of formula Iwherein R1is a hydrogen or an alkyl group, X is oxygen or NR5, where R5is a hydrogen or an alkyl group, and m is from 1 to 10, or the pharmaceutically acceptable salt thereof. In one aspect, when the neutral compound of formula I is used to produce the polymer, the resulting polymer can be subsequently reacted with an acid such as, for example, hydrochloric acid or ammonium chloride, to produce the polycationic salt.

[0108] In one aspect, in the compound of formula I, R1is methyl, X is NH, and m is 3. In another aspect, the monomer is methacrylamide, methacrylamide, A / -(2-hydroxypropyl)methacrylamide (HPMA), A / -[3-(A / '-dicarboxymethyl)aminopropyl]methacrylamide (DAMA), A / -(3- aminopropyl)methacrylamide, A / -(1,3-dihydroxypropan-2-yl) methacrylamide, N- isopropylmethacrylamide, N-hydroxyethylacrylamide (HEMA), or any combination thereof.

[0109] In a further aspect, the mole ratio of the guanidinyl monomer of formula I to the monomer is from 1:20 to 20:1, oris 1:20, 1:19, 1:18, 1:17, 1:16, 1:15, 1:14, 1:13, 1:12, 1:10, 1:9, 1:8, 1:7, 1:6, 1:5, 1:4, 1:3, 1:2, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1, or 20:1, where any ratio can be a lower and upper end-point of a range (e.g., 2:1 to 5:1, etc.). In one aspect, the mole ratio of the guanidinyl monomer of formula I to the monomer is from 3:1 to 4:1. In another aspect, the polyguanidinyl polymer is a homopolymer derived from the guanidinyl monomer of formula I.

[0110] The polyguanidinyl copolymer can be synthesized using polymerization techniques known in the literature such as, for example, RAFT polymerization (i.e. , reversible addition-fragmentationchain-transfer polymerization) or other methods such as free radical polymerization. In one aspect, the polymerization reaction can be carried out in an aqueous environment. As discussed above, the polyguanidinyl copolymer can be prepared initially as a neutral polymer followed by treatment with an acid to produce the pharmaceutically-acceptable salt.

[0111] In another aspect, multiple copolymers with controlled Mwand narrow polydispersity indices (PDIs) can be synthesized by RAFT polymerization. In one aspect, the pharmaceutically- acceptable salt of the polyguanidinyl copolymer has an average molecular weight (Mw) from about 1 kDa to about 100 kDa, or can be about 1 , 2, 3, 4, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or 100 kDa, where any value can be a lower and upper end-point of a range (e.g., 10 to 25 kDa, etc.).

[0112] In another aspect, the pharmaceutically-acceptable salt of the polyguanidinyl copolymer is a multimodal polyguanidinyl copolymer. The term “multimodal polyguanidinyl copolymer” is a polyguanidinyl copolymer with a molecular mass distribution curve being the sum of at least two or more molecular mass unimodal distribution curves. In one aspect, the polyguanidinyl copolymer has a multimodal distribution of polyguanidinyl copolymer molecular mass with modes between 5 and 100 kDa, or can be about 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or 100 kDa, where any value can be a lower and upper end-point of a range (e.g., 10 to 30 kDa, etc.).

[0113] In another aspect, the number of guanidinyl side groups in the pharmaceutically- acceptable salt of the polyguanidinyl copolymer can vary from about 10 to about 100 mol % of the. total polymer sidechains, or can be about 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or 100 mol %, where any value can be a lower and upper end-point of a range (e.g., 60 to 90 mol %, etc.). In one aspect, the guanidinyl side groups are from about 70 to about 80 mol % of the polyguanidinyl copolymer. Conversely, comonomer concentration can vary from about 50 to about 0 mol %, or can be about 50, 45, 40, 35, 30, 25, 20, 15, 10, 5, or 0 mol %, where any value can be a lower and upper end-point of a range (e.g., 10 to 40 mol %, etc.). In one aspect, the Mn, PDI, and structures of the copolymers can be verified by size exclusion chromatography (SEC),1H NMR, and13C NMR or other common techniques.

[0114] In one aspect, the polyguanidinyl polymer is from about 0.5 weight percent to about 15 weight percent of the hydrogel. In another aspect, the polyguanidinyl polymer is 0.5 weight percent, 1.0 weight percent, 2.0 weight percent, 3.0 weight percent, 4.0 weight percent, 5.0 weight percent, 6.0 weight percent, 7.0 weight percent, 8.0 weight percent, 9.0 weight percent, 10.0weight percent, 11.0 weight percent, 12.0 weight percent, 13.0 weight percent, 14.0 weight percent, or 15.0 weight percent of the hydrogel, where any value can be a lower and upper endpoint of a range (e.g., 3.0 weight percent to 8.0 weight percent).Polyanionic Polyelectrolytes

[0115] The polyanionic polyelectrolyte is a compound with a plurality of anionic groups or groups that can readily be converted to anionic groups. In one aspect, the polyanionic polyelectrolyte is a polymer having a plurality of anionic groups and pharmaceutically-acceptable cationic counterions. In another aspect, the polyanion has only anionic charged groups, i.e. no cationic groups. In one aspect, the polyanionic polyelectrolyte has from about 10 mol% to about 90 mol% anionic (i.e., ionized side chains) above pH 4.5 or about 10 mol%, 20 mol%, 30 mol%, 40 mol%, 50 mol%, 60 mol%, 70 mol%, 80 mol%, or 90 mol%, where any value can be a lower and upper endpoint of a range (e.g., 30 mol% to 70 mol%).

[0116] In one aspect, the polyanionic polyelectrolyte has a molecular weight from about 20 kDa to about 10,000 kDa, or 10 kDa, 50 kDa, 100 kDa, 500 kDa, 1 ,000 kDa, 2,000 kDa, 3,000 kDa, 4,000 kDa, 5,000 kDa, 6,000 kDa, 7,000 kDa, 8,000 kDa, 9,000 kDa, or 10,000 kDa, where any value can be a lower and upper endpoint of a range (e.g., 500 kDa to 6,000 kDa). In another aspect, the polyanionic polyelectrolyte comprises multiple molecular weight polymers to create a multimodal molecular weight distribution.

[0117] In one aspect, the polyanionic polyelectrolyte is derived by dissolving a polyanionic salt in water. In one aspect, the polyanionic salts described herein can be produced by adjusting the pH of a solution of a compound with a plurality of acidic groups (e.g., carboxylic acid groups) with the addition of a base to produce the corresponding anionic groups. In various aspects, bases which may be employed to form pharmaceutically acceptable polyanionic salts include alkali metal hydroxides, carbonates, acetate, etc. In one aspect, once the polyanion has been prepared, excess ions can be removed from the polyanion by filtration or dialysis prior to drying (e.g., lyophilization) to produce the polyanionic salt with stoichiometric amounts of cationic counterions relative to the number of anionic groups.

[0118] In one aspect, the cationic counterions of the polyanionic polyelectrolyte are monovalent cations such as, for example, sodium, potassium, or ammonium ions. In another aspect, the counterions of the polyanionic salt are multivalent ion such as, for example, calcium, magnesium ions, or mixtures thereof.

[0119] In one aspect, the polyanionic salt is composed of a polymer backbone with a plurality of anionic groups and pharmaceutically-acceptable cationic counterions. The anionic groups can be pendant to the polymer backbone and / or incorporated within the polymer backbone. In certain aspects, (e.g., biomedical applications), the polyanionic polyelectrolyte is any biocompatible polymer possessing anionic groups.

[0120] In one aspect, the polyanionic polyelectrolyte can be a pharmaceutically-acceptable salt of a synthetic polymer or naturally-occurring polymer. Examples of naturally-occurring polyanions include glycosaminoglycans such as chondroitin sulfate, heparin, heparin sulfate, dermatan sulfate, keratin sulfate, and hyaluronic acid. In other aspects, proteins having a net negative charge at neutral pH or proteins with a low pl can be used as naturally-occurring polyanions described herein. The anionic groups can be pendant to the polymer backbone and / or incorporated in the polymer backbone.

[0121] When the polyanionic polyelectrolyte is a synthetic polymer, it is generally any polymer possessing anionic groups or groups that can be ionized to anionic groups. Examples of groups that can be converted to anionic groups include, but are not limited to, carboxylate, sulfonate, boronate, sulfate, borate, phosphonate, or phosphate.

[0122] In one aspect, the polyanionic polyelectrolyte includes a polyacrylate having one or more pendant phosphate groups. For example, the polyanionic salt can be derived from the polymerization of acrylate monomers including, but not limited to, acrylates, methacrylates, acrylamides, methacrylamides, and the like. In other aspects, the polyanionic salt is a block copolymer, where segments or portions of the co-polymer possess anionic groups and neutral groups depending upon the selection of the monomers used to produce the co-polymer. In one aspect, the anionic group can be a plurality of carboxylate, sulfate, sulfonate, borate, boronate, phosphonate, or phosphate groups.In one aspect, the polyanionic polyelectrolyte is a polymer having a plurality of fragments of formula XIwherein R4is hydrogen or an alkyl group; n is from 1 to 10;Y is oxygen, sulfur, or NR30, wherein R30is hydrogen, an alkyl group, or an aryl group;Z’ is a pharmaceutically-acceptable salt of an anionic group.

[0123] In one aspect, Z’ in formula XI is carboxylate, sulfate, sulfonate, borate, boronate, a substituted or unsubstituted phosphate, or a phosphonate. In another aspect, Z’ in formula XI is sulfate, sulfonate, borate, boronate, a substituted or unsubstituted phosphate, or a phosphonate, and n in formulae XI is 2.

[0124] In one aspect, the polyanionic polyelectrolyte is a homopolymer of copolymer of acrylic acid. In one aspect, the homopolymer of copolymer of acrylic acid has a molecular weight from about 100 kDa to about 5,000 kDa, or about 100 kDa, 1,000 kDa, 1 ,500 kDa, 2,000 kDa, 2,500 kDa, 3,000 kDa, 3,500 kDa, 4,000 kDa, 4,500 kDa, or 5,000 kDa, where any value can be a lower and upper endpoint of arrange (e.g., 500 kDa to 3,500 kDa).

[0125] In one aspect, the polyanionic polyelectrolyte comprises a polyanionic polysaccharide. In one aspect, the polyanionic polysaccharide comprises negatively charged xanthan gum, hyaluronic acid, gellan gum, alginic acid, carrageenan, or any combination thereof.

[0126] In one aspect, the polyanionic polyelectrolyte is xanthan gum (xanthan), CAS 11138-66- 2, which consists of a cellulose based main chain with side chains of mannose and glucuronic acid. The side chains of xanthan interact with water and give it thickening and gelling properties in aqueous solutions. The anionic nature arises primarily from the glucuronic acid groups on side chains which contain carboxyl groups that ionize in water resulting in negatively chargedcarboxylate groups. A second negative charge comes from pyruvate groups coupled to the terminal mannose of the side chains which also contain carboxyl groups that ionize in water. The pyruvate content can vary based on the synthesis of xanthan and a higher pyruvate content will result in a higher concentration of negative charges per mol of xanthan and is desirable for PE hydrogel formation. Typically, about half of the side chains contain a pyruvate group, though modifications in the production or post-production can modify the amount of pyruvate content. In one aspect, the xanthan gum has a pyruvate content of more than 1.5 weight percent. In another aspect, the xanthan gum has a pyruvate content of less than 8.5 weight percent, or 1.5 weight percent, 2.5 weight percent, 3.5 weight percent, 4.5 weight percent, 5.5 weight percent, or less than 8.5 weight percent, where any value can be a lower and upper endpoint of arrange (e.g., 1.5 weight percent to 5.25 weight percent. Because xanthan gum is produced via fermentation of a gram-negative bacteria, prior to in vivo administration, endotoxins should be removed to less than 100EU per gram using a method such as that in US Patent No. 6,451,772B1. Above pH 4.5 xanthan is deprotonated and negatively charged. In one aspect, the potassium, calcium, and sodium salt of xanthan can be used herein.

[0127] In one aspect, the xanthan gum is a low acetate xanthan gum. The first mannose group on the side chain typically contains acetate groups. Acetate groups can be removed resulting in xanthan gums with a higher charge density and modified flow characteristics due to the more flexible chain that can be useful in polyelectrolyte hydrogels.

[0128] In one aspect, the xanthan gum has a molecular weight from about 100 kDa to about 10,000 kDa, or about 100 kDa, 500 kDa, 1,000 kDa, 1 ,500 kDa, 2,000 kDa, 2,500 kDa, 3,000 kDa, 3,500 kDa, 4,000 kDa, 4,500 kDa, 5,000 kDa, 5,500 kDa, 6,000 kDa, 6,500 kDa, 7,000 kDa, 7,500 kDa, 8,000 kDa, 8,500 kDa, 9,000 kDa, 9,500 kDa, or 10,000 kDa, where any value can be a lower and upper endpoint of arrange (e.g., 500 kDa to 7,500 kDa).

[0129] In one aspect, xanthan gum is from about 1.0 weight percent to about 15 weight percent of the hydrogel. In another aspect, xanthan gum is 1.0 weight percent, 2.0 weight percent, 3.0 weight percent, 4.0 weight percent, 5.0 weight percent, 6.0 weight percent, 7.0 weight percent, 8.0 weight percent, 9.0 weight percent, 10.0 weight percent, 11.0 weight percent, 12.0 weight percent, 13.0 weight percent, 14.0 weight percent, or 15.0 weight percent of the hydrogel, where any value can be a lower and upper endpoint of a range (e.g., 3.0 weight percent to 8.0 weight percent).

[0130] In another aspect, the polyanionic polyelectrolyte is the linear polysaccharide hyaluronic acid. Hyaluronic acid is composed of the monomers glucuronic acid and N-acetylglucosamine and is available in powder form as sodium hyaluronate in a range of molecular weights from less than 50,000 Da up to greater than 1 million Da. This range of molecular weight can be exploited to achieve the desired properties of the gel. When combined with an appropriate polycation, larger molecular weight hyaluronic acid will form a stronger PE hydrogel than smaller molecular weight hyaluronic acid. The charge density of hyaluronic acid at physiological pH is higher than xanthan gum, and a range of molecular weights can be used to create PE hydrogels that are deliverable through suitable catheters and are stable in physiological conditions. In one aspect, a combination of high molecular weight linear hyaluronic acid with a medium or lower molecular weight xanthan can create a PE hydrogel with a higher elastic modulus at low shear and improved deliverability relative to using only one type of anionic polysaccharide. In one aspect, the hyaluronic acid has a molecular weight from about 100 kDa to about 5,000 kDa, or about 100 kDa, 1 ,000 kDa, 1 ,500 kDa, 2,000 kDa, 2,500 kDa, 3,000 kDa, 3,500 kDa, 4,000 kDa, 4,500 kDa, or 5,000 kDa, where any value can be a lower and upper endpoint of arrange (e.g., 500 kDa to 3,500 kDa).

[0131] In another aspect, the polyanionic polyelectrolyte is gellan gum (CAS# 71010-52-1). Gellan gum is composed of repeat units of glucose, rhamnose, and glucuronic acid. Like xanthan and hyaluronic acid, gellan gum contains carboxyl groups on the glucuronic acid units that become negatively charged at physiological pH. Gellan gum comes in two main varieties, high acyl and low acyl which refers to the degree of acetylation and affects the physical properties. High acyl gellan gum generally creates more flexible and elastic structures whereas low acyl can form more firm and brittle gels. Gellan gum has a higher elastic modulus than xanthan gum and can be used as a sole polyanionic polyelectrolyte or combined with xanthan to increase the elastic modulus of the PE hydrogel while maintaining the delivery characteristics of a PE hydrogel with only xanthan used as the polyanion.

[0132] In another aspect, the polyanionic polyelectrolyte is from the carrageenan family consisting of kappa, iota, and lambda varieties. The negative charges on these molecules come from the presence of sulfate groups on the repeating galactose units that along with 3,6- andhydrogalactose form the backbone of the individual molecules. Lambda carrageenan has the lowest degree of sulfation and on its own will not form true gels. Kappa (K) and lota (I) both have a higher degree of sulfation and will form gels, with kappa forming the strongest gels. While the charge density of the carrageenans is generally higher than xanthan gum, the reduction inviscosity under shear is less pronounced and the elastic modulus of the PE hydrogels without a polycation counterion constituent higher. Like gellan gum, the carrageenan family of polyanions can be used to modify the PE hydrogel properties of other polyanions such as xanthan gum by increasing the elastic modulus of the PE hydrogel.

[0133] In another aspect, the polyanionic polyelectrolyte is alginate. Alginate is also an anionic polysaccharide composed of linear repeating chains of guluronic acid and mannuronic acid with carboxyl groups on both chain types. Like xanthan, the carboxyl groups fully deprotonate at physiological pH. Alginate also shows a reduction in viscosity under shear, though less than xanthan making it less preferred than xanthan for this application.

[0134] The amount of the of the polyanionic polyelectrolyte in the hydrogels described herein can vary depending upon the application of the hydrogel. In one aspect, the amount of the polyanionic polyelectrolyte used to produce the hydrogels described herein is from about 1 weight percent to about 12 weight percent of the hydrogel, or about 1 weight percent, 1 weight percent, 2 weight percent, 3 weight percent, 4 weight percent, 5 weight percent, 6 weight percent, 7 weight percent, 8 weight percent, 9 weight percent, 10 weight percent, 11 weight percent, or 12 weight percent, where any value can be a lower and upper end-point of a range (e.g., 5 weight percent to 8 weight percent, etc.).Monovalent and Divalent Ions

[0135] In one aspect, the addition of monovalent ions in the form of a salt such as, for example sodium chloride and potassium chloride creates a homogeneous PE hydrogel. In the absence of the monovalent ions, the polyelectrolytes can clump together and create a solution with phase separation or crash out into small particles. Increasing the concentration of monovalent ions increases the transparency of the gel, indicating shielding of ionic bonding between the larger polyelectrolytes. In one aspect, when the polyanion is xanthan gum, monovalent salt counterions also increase the viscosity and elastic modulus of the gel.

[0136] In one aspect, divalent cations can be used in combination with the polycationic polyelectrolyte. For example, calcium chloride and magnesium chloride have properties that can also be useful in the formation and use of hydrogel embolics. Divalent cations can crosslink between branches of a polyanion rather than shielding the larger polycation and polyanion like monovalent ions. Due to these properties, divalent ions can be used to reduce the concentration of the larger polycation while maintaining the same charge ratio. This is useful to reduce overall viscosity and improve the delivery of the PE hydrogel embolic. Divalent ions can also be used toincrease the charge ratio to make a positively charged embolic with a lower viscosity than a PE hydrogel with a net positive charge comprised of only larger polycation molecules. Divalent ions such as calcium can also help activate the clotting cascade and can be useful in the application of PE hydrogel embolics in the treatment of hemorrhage.

[0137] The selection of polyelectrolyte and the concentration of polyelectrolyte affect the amount of salt counterions needed to create a homogeneous PE hydrogel. In one aspect, the concentration of the salt counterions in the hydrogel is from about 0.1 M to about 2.5 M, or about 0.1 M, 0.2 M, 0.4 M, 0.6 M, 0.8 M, 1.0 M, 1.2 M, 1.4 M, 1.6 M, 1.8 M, 2.0 M, 2.2 M, 2.4 M, or 2.5 M, where any value can be a lower and upper end-point of a range (e.g., 0.8 M to 1.6 M, etc.). In one aspect, when the polyanionic polyelectrolyte is xanthan, the charge molarity of the monovalent and / or divalent ions required to form a homogeneous PE hydrogel is from about 0.35 M to about 2.0 M. In another aspect, when the polyanionic polyelectrolyte is hyaluronic acid, the concentration of the monovalent and / or divalent ions required to form a homogeneous PE hydrogel is from about 0.1 M to about 2.5M.Contrast Agents

[0138] The hydrogels described herein can include one or more contrast agents that permit the visualization of the hydrogel after it has been administered to the subject.

[0139] In one aspect, the contrast agent is a radiographic contrast agent. Further in this aspect, the radiographic contrast agent can be tantalum metal particles (Ta), gold particles, or an iodide salt (e.g., sodium iodide). In one aspect, up to 30 % (w / w) of Ta can be included in the formulations. In one aspect, inclusion of Ta can be beneficial to interventional radiologists in the operating room. In another aspect, the contrast agent can be a fluoroscopic contrast agent. Further in this aspect, the fluoroscopic contrast agent can be tantalum oxide (TaC>2, Ta2Os) particles. In one aspect, the contrast agent can be tantalum particles having a particle size from 0.5 pm to 50 pm, 1 pm to 25 pm, 1 pm to 10 pm, or 1 pm to 5 pm. In another aspect, contrast agent is tantalum particles in the amount of 10% to 60%, 20% to 50%, or 20% to 40%.

[0140] The hydrogels described herein include one or more transient contrast agents, where the contrast agent readily diffuses out of the hydrogel upon administration to the subject, providing temporary contrast.

[0141] In one aspect, the transient contrast agent is a non-ionic compound. In another aspect, the transient contrast agent is water-soluble. In one aspect, the transient contrast agent is aniodinated organic compound, where one or more iodine atoms are covalently bonded to the organic compound. Iodinated organic contrast agents are a class of iodine-containing organic compounds. This set of compounds are derivatives of 2,3,5-triidobenzoic acid to produce different commercially available compounds, such as iopamidol, iodixanol, iohexol, iopromide, iobtiridol, iomeprol, iopentol, iopamiron, ioxilan, iotrolan, iotrol and ioversol, iopanoate, diatrizoic acid, iothalamate, and ioxaglate, various side chains are added to the parent compound. These sidechains modify the solubility, toxicity, and osmolality of the compound. Iodixanol is a dimer of the parent compound, producing a molecule with 6 iodine atoms. Structures for these compounds and the parent compound 2, 3, 5-triidobenzoic acid are shown in Figure 2. In another aspect, the iodinated organic compound is an iodinated oil such as, for example, ethiodized poppyseed oil (Lipiodol).

[0142] The concentration of the transient contrast agent in the hydrogels can vary depending upon the application. In one aspect, the concentration of the transient contrast agent in the hydrogel is from 10 mgl / mL to 1,000 mgl / mL, or is 10 mgl / mL, 25 mgl / mL, 50 mgl / mL, 75 mgl / mL, 100 mgl / mL, 125 mgl / mL, 150 mgl / mL, 175 mgl / mL, 200 mgl / mL, 225 mgl / mL, 250 mgl / mL, 275 mgl / mL, 300 mgl / mL, 325 mgl / mL, 350 mgl / mL, 375 mgl / mL, 400 mgl / mL, 425 mgl / mL, 450 mgl / mL, 475 mgl / mL, 500 mgl / mL, 525 mgl / mL, 550 mgl / mL, 575 mgl / mL, 600 mgl / mL, 625 mgl / mL, 650 mgl / mL, 675 mgl / mL, 700 mgl / mL, 725 mgl / mL, 750 mgl / mL, 775 mgl / mL, 800 mgl / mL, 825 mgl / mL, 850 mgl / mL, 875 mgl / mL, 900 mgl / mL, 925 mgl / mL, 950 mgl / mL, 975 mgl / mL, or 1 ,000 mgl / mL, 100 mgl / mL, 100 mgl / mL, 100 mgl / mL, 100 mgl / mL, 100 mgl / mL, 100 mgl / mL, where any value can be a lower and upper end-point of a range (e g., 400 mgl / mL to 600 mgl / mL, etc.).

[0143] In one aspect, the majority of the transient contrast agent that diffuses from the hydrogel is such that the transient contrast agent cannot be detected by imaging techniques such as, for example, fluoroscopy or CT. In one aspect, up to 70%, up to 80%, up to 90%, up to 95%, or up to 100% of the transient contrast agent diffuses out of the solid from 5 minutes to 48 hours once the solid is produced in situ, or 5 minutes, 10 minutes, 30 minutes, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 18 hours, 24 hours, 30 hours, 36 hours, 42 hours, or 48 hours, 2 days, 5 days, 10 days, 15 days, 20 days, 25 days, or 30 days, where any value can be a lower and upper end-point of a range (e.g., 1 hour to 3 hours, etc.).Polyelectrolyte Hydrogel Modifiers

[0144] Although the properties of the hydrogels described herein are highly modifiable through changes in charge ratio and relative amounts of the polycationic and polyanionic polyelectrolytes, and the concentration of the monovalent ions, the properties of the PE hydrogel can be further modified through additional compounds.

[0145] In one aspect, the modifier comprises natural or synthetic fibers, water-insoluble filler particles, nanoparticles, or microparticles can be added to the hydrogels. When fibers are added to the hydrogels, the fibers can be charged or uncharged, with linear or branched morphology. The fibers can both reinforce the PE hydrogel and undergo similar deformation to the polymer chains under shear, creating a greater decrease in elastic modulus and viscosity under shear during delivery through a catheter. In one aspect, the fibers comprise a milled and sieved thermally crosslinked gelatin foam fiber. An example of such a fiber is SURGIFOAM® manufactured by Ethicon, which is water-insoluble porcine gelatin. In one aspect, the amount of fiber that is present in the hydrogels is from 0.1 weight percent to 5 weight percent, or about 0.1 weight percent, 0.1 weight percent, 0.5 weight percent, 1.0 weight percent, 1.5 weight percent, 2.0 weight percent, 2.5 weight percent, 3.0 weight percent, 3.5 weight percent, 4.0 weight percent, 4.5 weight percent, or 5.0 weight percent, where any value can be a lower and upper end-point of a range (e.g., 1.5 weight percent to 4.0 weight percent, etc.).

[0146] In one aspect, the modifier comprises fibers made from crosslinked gelatin. Gelatin alone does not shear thin and has a melting point below body temperature but above room temperature making performance inconsistent during delivery due to the temperature difference in the catheter outside the body and inside the body. However, crosslinked gelatin is stable across a wide range of temperatures and exhibits shear thinning behavior complementary to the other components in the PE hydrogel. It also can provide a mechanical barrier to flow depending on its size and shape.

[0147] In one aspect, the modifier comprises thermally crosslinked gelatin fibers or particles made from type A porcine derived gelatin with an isoelectric point between pH 6-8. Below the isoelectric point the net charge will be positive and above the isoelectric point it will be negative. The charge density of gelatin is low and once crosslinked it is further reduced, however, the net charge of the fibers or particles can be chosen to optimize interactions with the other components of the polyelectrolyte hydrogel.

[0148] In one aspect, the modifier comprises thermally crosslinked gelatin fibers or particles made from type B porcine derived gelatin with an isoelectric point between pH 4.5-5.5. Below the isoelectric point the net charge will be positive and above the isoelectric point it will be negative.The charge density of gelatin is low and once crosslinked it is further reduced, however, the net charge of the fibers or particles can be chosen to optimize interactions with the other components of the polyelectrolyte hydrogel. For example, in PE hydrogels containing chitosan with an excess of positive charge relative to the negatively charged polyanion and a pH between 5.5-6.0, there will be weak interactions between the chitosan and the negatively charged regions of the crosslinked type B gelatin.

[0149] In one aspect, the crosslinked gelatin has on average a length of greater than 100 pm and a width less than 25 pm. In another aspect, the crosslinked gelatin has a maximum dimension between 100-500 pm and a minimum dimension less than 100 pm. This will provide an additional barrier to flow in small vessels less than 300 pm in diameter but will not affect the force to inject the PE hydrogel. In another aspect, the crosslinked gelatin has a maximum dimension between 500 pm and 1000 pm and a minimum dimension less than 500 pm. In another aspect, the crosslinked gelatin has a maximum dimension between 700 pm and 1 ,100 pm and a minimum dimension less than 700 pm. In another aspect, the crosslinked gelatin has a maximum dimension greater than 1 ,100 pm and less than 2,000 pm.

[0150] In another aspect, the PE hydrogel modifier includes a nonionic polysaccharide. Examples of the nonionic polysaccharides include, but are not limited to, guar gum, locust bean gum, a modified starch, or a combination thereof. The nonionic polysaccharide can increase the PE hydrogel strength of the composition while maintaining reversible viscosity reduction during catheter delivery. The molecular weight of the nonionic polysaccharide can be selected to achieve the desired properties. In one aspect, the amount of nonionic polysaccharide that is present in the hydrogels is from 0.1 weight percent to 5 weight percent, or about 0.1 weight percent, 0.1 weight percent, 0.5 weight percent, 1.0 weight percent, 1.5 weight percent, 2.0 weight percent, 2.5 weight percent, 3.0 weight percent, 3.5 weight percent, 4.0 weight percent, 4.5 weight percent, or 5.0 weight percent, where any value can be a lower and upper end-point of a range (e.g., 1.5 weight percent to 4.0 weight percent, etc.).

[0151] In another aspect, the PE hydrogel modifier can be composed of organic and / or inorganic materials. In one aspect, the nanostructures can be composed of organic materials like carbon or inorganic materials including, but not limited to, boron, molybdenum, tungsten, silicon, titanium, copper, bismuth, tungsten carbide, aluminum oxide, titanium dioxide, molybdenum disulphide, silicon carbide, titanium diboride, boron nitride, dysprosium oxide, iron (III) oxide-hydroxide, iron oxide, manganese oxide, titanium dioxide, boron carbide, aluminum nitride, or any combinationthereof. In another aspect, the PE hydrogel modifier comprises a metal oxide, a ceramic particle, or a water insoluble inorganic salt. In one aspect, the amount of organic or inorganic material that is present in the hydrogels is from 0.1 weight percent to 5 weight percent, or about 0.1 weight percent, 0.1 weight percent, 0.5 weight percent, 1 .0 weight percent, 1.5 weight percent, 2.0 weight percent, 2.5 weight percent, 3.0 weight percent, 3.5 weight percent, 4.0 weight percent, 4.5 weight percent, or 5.0 weight percent, where any value can be a lower and upper end-point of a range (e.g., 1 .5 weight percent to 4.0 weight percent, etc.).

[0152] In another aspect, the PE hydrogel modifier comprises a synthetic or natural silicate nanoparticle including, but not limited to, bentonite, kaolinite, montmorillonite, saponite, hectorite, palygorskite, laponite, stevensite, or any combination thereof. In one aspect, the amount of synthetic or natural silicate nanoparticle that is present in the hydrogels is from 0.1 weight percent to 5 weight percent, or about 0.1 weight percent, 0.1 weight percent, 0.5 weight percent, 1.0 weight percent, 1.5 weight percent, 2.0 weight percent, 2.5 weight percent, 3.0 weight percent, 3.5 weight percent, 4.0 weight percent, 4.5 weight percent, or 5.0 weight percent, where any value can be a lower and upper end-point of a range (e.g., 1.5 weight percent to 4.0 weight percent, etc.).Bioactive Agents

[0153] The hydrogels described herein can include one or more bioactive agents. In one aspect, the bioactive agent is an antibiotic, a pain reliever, an immune modulator, a growth factor, an enzyme inhibitor, a hormone, a messenger molecule, a cell signaling molecule, a receptor agonist, an oncolytic virus, a chemotherapy agent, an anti-angiogenic agent, a receptor antagonist, a nucleic acid, or any combination thereof.

[0154] In one aspect, the bioactive agent can be a nucleic acid. The nucleic acid can be an oligonucleotide, deoxyribonucleic acid (DNA), ribonucleic acid (RNA) including mRNA, or peptide nucleic acid (PNA). The nucleic acid of interest can be a nucleic acid from any source, such as a nucleic acid obtained from cells in which it occurs in nature, recombinantly produced nucleic acid, or chemically synthesized nucleic acid, or chemically modified nucleic acids. For example, the nucleic acid can be cDNA or genomic DNA or DNA synthesized to have the nucleotide sequence corresponding to that of naturally-occurring DNA. The nucleic acid can also be a mutated or altered form of nucleic acid (e.g., DNA that differs from a naturally occurring DNA by an alteration, deletion, substitution or addition of at least one nucleic acid residue) or nucleic acid that does not occur in nature.

[0155] In one aspect, the bioactive agent is an FDA-approved anti-angiogenic agent. In one aspect, the anti-angiogenic agent is a tyrosine kinase inhibitor (TKI). Not wishing to be bound by theory, angiogenesis is, in large part, initiated and maintained by cell signaling through receptor tyrosine kinases (RTKs). In one aspect, RTKs include receptors for several angiogenesis promoters, including VEGF, which stimulates vascular permeability, proliferation, and migration of endothelial cells; PDGF, which recruits pericytes and smooth muscle cells that support the budding endothelium; and FGF, which stimulates proliferation of endothelial cells, smooth muscle cells, and fibroblasts. In one aspect, the anti-angiogenic agent is a TKI such as sunitinib malate (SUN), pazopanib hydrochloride (PAZ), sorafenib tosylate (SOR), vandetanib (VAN), cabozantinib, or any combination thereof.

[0156] In another aspect, the bioactive agent can be humanized anti-VEGF and anti- VEGFR Fab' fragments. In this aspect, electrostatic interactions can control release kinetics. In one aspect, the native charge of the Fab' fragment is sufficient to interact with the polyelectrolyte components in the injectable composition. In another aspect, the native charge of the Fab' fragment is insufficient to interact with the polyelectrolyte components in the injectable composition and the Fab' fragment is modified to increase charge density by attaching a short polyelectrolyte to reactive sulfhydryl groups using maleamide conjugation chemistries.

[0157] In one aspect, the anti-angiogenic agent is an anti-VEGF antibody. In a still further aspect, the anti-VEGF antibody is bevacizumab or is a biosimilar anti-VEGF antibody, or is an anti-VEGF antibody derivative such as, for example, ranibizumab.

[0158] The rate of release can be controlled by the selection of the materials used to prepare the hydrogels, as well as the charge of the bioactive agent if the agent has ionizable groups. Thus, in this aspect, the hydrogel once administered to the subject can perform as a localized controlled drug release depot.Preparation of the Polyelectrolyte Hydrogels

[0159] The preparation of the PE hydrogels described herein can be performed using a number of techniques and procedures. Exemplary techniques for producing the hydrogels are provided in the Examples. In one aspect, an aqueous solution comprising the polyanionic polyelectrolyte is added to an aqueous solution comprising the polyanionic polyelectrolyte and the monovalent ions followed by mixing for a sufficient time and intensity to produce a homogeneous gel. Theintensity and duration of mixing will vary depending upon the selection and amounts of components used to produce the hydrogel.

[0160] In the case when additional components (e.g., contrast agents, PE hydrogel modifiers, bioactive agents) are to be incorporated into hydrogels, in one aspect, these components are added prior to and / or during the mixing of the polycationic and polyanionic polyelectrolytes and monovalent ions. In other aspect, these components can be added to the hydrogel after it has been formed.

[0161] In one aspect, the pH of the hydrogel is from 4.5 to 6, 6 to 9, 6.5 to 8.5, 7 to 8, or 7 to 7.5. In another aspect, the pH of the composition is 7.4, which is the normal physiological pH in blood.Applications of the Polyelectrolyte Hydrogels

[0162] The polyelectrolyte hydrogels described herein have numerous benefits and biomedical applications. As discussed above, the hydrogels are readily injectable via a narrow-gauge device, catheter, needle, cannula, or tubing. The hydrogels are water-borne eliminating the need for potentially toxic solvents.

[0163] The ability to modify or fine-tune the properties of the PE hydrogels described herein makes them suitable for occluding vessels over a wide range of diameters and sizes. In one aspect, the polyelectrolyte PE hydrogel is suitable for occlusion of flow in a vessel with a minimum inner diameter greater than 500 pm (e.g., 500 pm to 1 ,000 pm). In another aspect, a tapering vessel can be filled with PE hydrogel from distal to proximal to occlude flow in a proximal vessel, with inner diameter greater than 1000 pm and less than 3000 pm, when the inner diameter of the distal tapering portion of the vessel is less than 1000 pm. In another aspect, the hydrogel is suitable for occlusion of flow in a vessel with inner diameter ranging from about 30 pm to about 100 pm. In another aspect, the hydrogel is suitable for occlusion of flow in a vessel with an inner diameter ranging from 100 pm to 300 pm. In another aspect, the hydrogel is suitable for occlusion of flow in a vessel with an inner diameter ranging from about 300 pm to 700 pm. In another aspect, the hydrogel is suitable for occlusion of flow in a vessel with an inner diameter ranging from 700 pm to 2000 pm.

[0164] In practice, embolic agents are selected based on the size of catheter they can be delivered through and the inner diameter of the vessel to be occluded. The same approach can be followed when using the PE hydrogels described herein by preparing hydrogels with the appropriate low shear viscosity and elastic modulus G’ to occlude a vessel of a given size pairedwith acceptable injection force levels through the desired catheter. The following table provides non-limiting, exemplary parameters for hydrogels for use with a desired catheter size and vessel inner diameter. The values provided in the table are based on the maximum acceptable injection force for a given catheter size that does not exceed the burst pressure of the lowest published burst pressure of commercially available catheters. The injection force can be reduced by reducing the polyelectrolyte concentration, changing the charge ratio to favor the less viscous polyelectrolyte component, decreasing salt counterion molarity, and inclusion of an appropriate amount of fibers in addition to or in place of viscous polymers. The blood pressure drops with decreasing vessel size, especially at the arteriole level which starts at around 300 pm. Therefore, to effectively occlude vessels in that range, a lower elastic modulus is required and the embolic need only reliably fill space and remain cohesive and insoluble. To effectively plug larger vessels, the charge ratio and polyelectrolyte concentrations can be tailored to achieve greater cohesion and higher elastic modulus. Additionally, non-ionic modifiers, adjustment of crosslinked gelatin or other fiber size, shape and concentration, clotting enhancement, and endothelial adhesion can all be balanced to get the desired level of occlusion.*When delivered in a volume that is less than half the dead volume of the delivery catheter and pushed with low viscosity liquid such as 0.9% saline.

[0165] In one aspect, the PE hydrogels described herein form a right- or left-handed coil during delivery through a catheter, needle, or other delivery device. The PE hydrogels can retain the shape of the delivery catheter in physiological conditions, which provides a number of advantages with respect to using the PE hydrogels as embolic agents. Catheters can be selected to create a desired gel-coil diameter. Additionally, a wide range of vessel sizes can be occluded dependingon the catheter size, the flow conditions, vessel tapering, and amount of material delivered. A larger amount of material delivered to the vessel will form a denser coil mass and occlude larger vessels.

[0166] Another advantage of coil formation is that the shape of the catheter tip can be designed to deliver a particular shape or size of material or influence the behavior. For example, an angled catheter tip will increase the cross-sectional area of delivery and direct the material into the vessel wall to initiate the coiling process. Catheter tip designs that bifurcate the lumen will result in splitting the embolic into two coil streams delivered simultaneously. A wide range of custom behaviors are therefore achievable due to the combination of the PE hydrogel properties and catheter design.

[0167] In another aspect, the PE hydrogels will initially retain the shape of the catheter during delivery into a vessel but will subsequently form an amorphous mass of PE hydrogel material that conforms to the anatomy of the vessel.

[0168] In one aspect, the PE hydrogels described herein can be delivered in a smaller volume by first introducing the desired volume from a syringe into a delivery device (e.g., O.IOmL) and then subsequently pushing the smaller volume of the PE hydrogel through a catheter or needle with a second fluid.

[0169] A unique aspect of the PE hydrogels described herein is that due to the increased cohesion of the hydrogels after exposure to physiological media, a smaller volume of the PE hydrogels can be pushed through a catheter with one of the liquids described below and delivered to the target embolization site without diluting or weakening the portion of the hydrogel in contact with the liquid. This approach has several advantages.

[0170] (1) The force of delivery is reduced, and the PE hydrogel pledgets can be pushed through catheters with an inner diameters < 0.20” and lengths up to 220cm. This allows the PE hydrogels to not have limitations in their application including use in prostatic artery embolization, geniculate artery embolization, or neurological applications that often use long catheters with a small inner diameter;

[0171] (2) The lumen of the catheter is left empty after injection without residue of the PE hydrogel which allows the catheter to be used for additional contrast runs for imaging. It also can reduce the cost of complex procedures that may require multiple injections by conserving catheters. Existing tantalum containing liquid or hydrogel embolization agents will either be diluted and losestrength or solidify and plug the catheter or leave remnants of solidified material in the catheter which can present a risk of off-target embolization if the catheter continues to be used.

[0172] (3) The PE hydrogels behave as both a coil and a pledget or plug. They exit the catheter with a coil-like shape but compact on themselves to achieve a near 100% packing density similar to a plug or pledget. In contrast to traditional pledgets made of crosslinked gelatin or similar material, these PE hydrogels can be loaded with tantalum or other contrast agent and made highly visible. They are also permanent, more like a coil than gelatin pledgets, but without the difficulty of achieving the desired packing density and demonstrate near immediate occlusion without relying on clotting.

[0173] (4) Ability to plug larger due to the ability to increase the concentration of polyelectrolyte components and the strengthening of the PE hydrogel along the contact area with the aqueous pushing medium.

[0174] In one aspect, wherein the polyelectrolyte hydrogel is first introduced into the subject by a delivery system followed by introducing a low viscosity liquid, a hydrophobic liquid, an aqueous contrast agent, or any combination thereof into the subject by a syringe, wherein the syringe is connected to the delivery system. This aspect is depicted in FIGS. 27A-F. Referring to FIGS. 27A-B, the delivery system 1 includes a housing 2 having a first end 3 and a second end 4, an interior chamber 5 within the housing for containing the polyelectrolyte hydrogel, a male Luer connection 6 at the first end of the housing, and a female Luer connection 7 at the second end of the housing. In one aspect, a needle or catheter 8 attached to the male Luer connection 6,

[0175] In one aspect, the female Luer connection 7 can receive a syringe 9 (FIG. 27E), which contains the liquid to be injected with the polyelectrolyte hydrogel. When the liquid from syringe 9 is injected into the delivery system 1 containing the polyelectrolyte hydrogel, the polyelectrolyte hydrogel is pushed through the catheter or needle 8 (FIG. 27E) and administered the subject.

[0176] In one aspect, the liquid to be injected with the polyelectrolyte hydrogel is a low viscosity liquid. Examples of low viscosity liquids include, but are not limited to, saline (e.g., less than 2%), a non-ionic iodinated contrast agent in water, dextrose (5% or D5W), or sterile water for injection. For example, the PE hydrogel can be formulated such that during the delivery of a small volume of hydrogel (e.g., between 0.020mL and 0.40mL) with 0.9% saline or aqueous based contrast agent, the PE hydrogel increases its elastic modulus due to the diffusion of salts into the pushing medium. The PE hydrogel will remain highly cohesive without dilution to the proximal end in contact with the pushing medium. The pushing medium may push beyond the proximal end of thePE hydrogel during delivery facilitating ion diffusion along a greater length of the PE hydrogel and elongating the hydrogel prior to delivery while also strengthening the PE hydrogel by allowing greater electrostatic bonding due to a reduction in the shielding provided by the salt counterions.

[0177] In another aspect, a small volume of the PE hydrogels is delivered with a hydrophobic liquid such as, for example, ethiodized oil (Lipiodol), a silicone, a plant-derived oil (e.g., sesame oil), or other suitable biocompatible hydrophobic liquids.

[0178] In one aspect, the PE hydrogels can be used to reduce or inhibit blood flow in a vessel of a subject. In one aspect, the vessel is a blood vessel or duct (e.g., lymphatic duct). In one aspect, the PE hydrogels can be used to reduce or inhibit flow from a lymph duct. In one aspect, the PE hydrogels can be used to reduce or inhibit flow of lymph from the right lymphatic duct, the thoracic duct, or both. In these aspects, the hydrogel creates an artificial embolus within the vessel or duct. Thus, the PE hydrogels described herein can be used as synthetic embolic agents. In this aspect, the hydrogel is injected into the vessel to partially or completely block the blood vessel. This method has numerous applications including the creation of an artificial embolism to inhibit blood flow to a tumor, an aneurysm, an endoleak, a varicose vein, a varicocele, a gonadal vein, the portal vein, a vascular malformation, geniculate artery, uterine fibroids, an ovarian vein, a pelvic vein, a gastrointestinal artery, a rectal artery, a mesenteric artery, the gastroduodenal artery, hepatic artery, the splenic artery, an iliac artery, a prostatic artery, hemorrhoids, middle meningeal artery, or a bleeding wound, or other vascular trauma or defects. In other aspects, the injectable compositions can be administered in other areas in the subject including lymphatic ducts, airways, and other channels where it is desirable to form an occlusion in a medical application. In another aspect, the hydrogels described herein can be used to treat pain in a musculoskeletal region such as, for example a joint. In one aspect, the hydrogels can temporarily reduce or prevent flow in a joint such as an elbow, knee, or shoulder where pain is occurring.

[0179] As discussed above, the PE hydrogels can be used as synthetic embolic agents. However, in other aspects, the hydrogels described herein can include or be used in combination with one or more additional embolic agents. In one aspect, the additional embolic includes coils, plugs, liquid embolics, or gelatin foam. Embolic agents commercially-available are microparticles used for embolization of blood vessels. The size and shape of the microparticles can vary. In one aspect, the microparticles can be composed of polymeric materials. An example of this is Bearin™ nsPVA particles manufactured by Merit Medical Systems, Inc., which are composed of polyvinyl alcohol ranging in size from 45 pm to 1,180 pm. In another aspect, the embolic agentcan be a microsphere composed of a polymeric material. Examples of such embolic agents include Embosphere® Microspheres, which are made from trisacryl cross-linked gelatin ranging in size from 40 pm to 1,200 pm; HepaSphere™ Microspheres (spherical, hydrophilic microspheres made from vinyl acetate and methyl acrylate) ranging in size from 30 pm to 200 pm; and QuadraSphere® Microspheres (spherical, hydrophilic microspheres made from vinyl acetate and methyl acrylate) ranging in size from 30 pm to 200 pm, all of which are manufactured by Merit Medical Systems, Inc. In another aspect, the microsphere can be impregnated with one or more metals that can be used as a contrast agent. An example of this is EmboGold® Microspheres manufactured by Merit Medical Systems, Inc., which are made from cross-linked trisacryl gelatin impregnated with 2% elemental gold ranging in size from 40 pm to 1 ,200 pm.

[0180] In another aspect, the hydrogels described herein can be used to treat hemorrhage. In one aspect, the hemorrhage is the result of trauma. In one aspect, the hemorrhage is treated endovascularly. In one aspect, the hydrogel is administered at the site of the hemorrhage. Furthermore, the efficacy of treating the hemorrhage can be adjusted through modifying the charge ratio of the polyelectrolytes, the monovalent and / or divalent ion concentration, the selection of the polyelectrolytes, and the inclusion of additional components.

[0181] In another aspect, the hydrogels described herein can be used in combination with one or more mechanical vascular devices such as, for example, embolic coils, fibers, and the like. In one aspect, the mechanical embolic is first administered to a vessel in the subject using techniques known in the art followed by the administration of the hydrogel to the vessel within or in close proximity to the mechanical device.

[0182] In one aspect, the hydrogels can be used to reinforce the inner wall of a blood vessel in the subject. The hydrogels can be introduced into the vessel at a sufficient volume to coat the inner lining of the vessel so that the vessel is not fully occluded. For example, the hydrogel can be injected into a blood vessel where there is an aneurysm. Here, the hydrogels can reduce or prevent the rupture of an aneurysm.

[0183] In one aspect, the hydrogels can be used to close or seal a puncture in a blood vessel in the subject. In one aspect, the hydrogels can be injected into a vessel at a sufficient amount to close or seal the puncture from within the vessel so that the vessel is not blocked. In another embodiment, the hydrogels can be applied to a puncture on the exterior surface of the vessel to seal the puncture.

[0184] In another aspect, the hydrogels described herein can be used to fill a void in a subject.ln certain conditions, it is desirable to fill a void in a subject to prevent or avoid significant health risks. The void can be a closed or open space in the subject created by bone, muscle, skin, cartilage, tissue, or a combination thereof in the subject. In one aspect, the hydrogel can be delivered into the void with the use of a catheter or needle. In one aspect, the void can be completely filled by the hydrogel. In another aspect, the void can be partially filled (i.e., less than 100%) by the hydrogel.

[0185] In one aspect, the void is a left atrial appendage (LAA). A left atrial appendage (LAA) is a small pouch found in the top left of the heart (the left atrium). The LAA can facilitate the development of blood clots in people with atrial fibrillation (~6 million), putting them at a higher risk of stroke. These patients can be treated with medications, with surgery, or with an interventional procedure.

[0186] There are two common LAA closure devices, the Watchman (Boston Scientific) and the Amplatzer Amulet (Abbott). Both use a trans-septal approach, piercing the septum of the right and left atrium to allow the passage of a large 12-14Fr catheter which delivers a closure device that anchors at and seals off the opening of the LAA.

[0187] The hydrogels described herein can be delivered through catheter or needle without the need to pierce the atrial septum. The hydrogel could be delivered by catheter through the left ventricle to the left atrium (FIG. 16) and will fill and close the left atrial appendage. The hydrogel fills the available space within the LAA and strengthens over the course of several minutes. As it strengthens, the material is sterically held in place by the ridges of the LAA topography.

[0188] In another aspect, the hydrogels described herein can fill a void in a lymph node is addition to reducing or inhibiting flow of lymph from the right lymphatic duct, the thoracic duct, or both. Here, the hydrogel can be delivered into the lymph to reduce or prevent the flow of lymph to the lymph ducts.

[0189] In other aspects, the hydrogels described herein can encapsulate, scaffold, seal, or hold one or more bioactive agents. Thus, the hydrogels can be used as a delivery device or implantable drug depot.Kits

[0190] Described herein are kits for making and using the hydrogels. In one aspect, the kit includes (a) a first syringe comprising the polyelectrolyte hydrogel as described herein, (b) and (d) instructions for administering the hydrogel to a subject.

[0191] In one aspect, the hydrogel can be prepared using the techniques described above then subsequently introduced into a first syringe. In one aspect, the hydrogel can include optional components such as contrast agents, PE hydrogel modifiers, and bioactive agents as described herein. In other aspects, the kit can include a second syringe that includes optional components such as contrast agents, PE hydrogel modifiers, and bioactive. In this aspect, the optional component can be prepared as a water or saline solution prior to introduction into the second syringe. In one aspect, the second syringe is attached to the first syringe with a female-female luer adapter. Here, the contents in the second syringe are introduced into the first syringe with the hydrogel. After the contents of the second syringe have been introduced int the first syringe, the hydrogel can be administered to the subject via the first syringe.

[0192] The kits also include instructions for administering the hydrogels to the subject. As used herein, “instruction(s)” means documents describing relevant materials or methodologies pertaining to a kit. These materials may include any combination of the following: background information, list of components and their availability information (purchase information, etc.), brief or detailed protocols for using the kit, trouble-shooting, references, technical support, and any other related documents. Instructions can be supplied with the kit or as a separate member component, either as a paper form or an electronic form which may be supplied on computer readable memory device or downloaded from an internet website, or as recorded presentation. Instructions can include one or multiple documents and are meant to include future updates.

[0193] The kits can also include additional components as described herein can include optional mechanical components such as, for example, additional syringes, microcatheters, introducer tips, and other devices for delivering the hydrogel described herein to the subject.

[0194] In one aspect, the kit includes a delivery system comprising the polyelectrolyte hydrogel as described herein contained within the delivery system; the polyelectrolyte hydrogel; and instructions for administering the polyelectrolyte hydrogel to a subject.

[0195] In this aspect, the polyelectrolyte hydrogel is stored in the delivery system. Referring to FIG. 27F, the delivery system 1 can have caps 10 and 11 at each end of the delivery system. When ready for use, each cap can be removed sequentially to attach the catheter or needle and syringe to the delivery device

[0196] In another aspect, the kit includes a delivery system for delivering the polyelectrolyte hydrogel as described herein; a polyelectrolyte hydrogel; and instructions for administering the polyelectrolyte hydrogel to a subject.

[0197] In this aspect, the polyelectrolyte hydrogel is stored outside the delivery system. For example, the polyelectrolyte hydrogel can be stored in dry or aqueous form in a vial. When ready for use, the polyelectrolyte hydrogel can be introduced into the delivery system.

[0198] In one aspect, the kit can include a syringe containing a low viscosity liquid, a hydrophobic liquid, an aqueous contrast agent, or any combination thereof as described above. In the alternative, the kit can include an empty syringe and a vial of the low viscosity liquid, a hydrophobic liquid, an aqueous contrast agent, or any combination thereof. In one aspect, when a low viscosity liquid is used, the liquid can include additional components such as, for example, lidocaine, nitroglycerin, or verapamil.

[0199] Now having described the aspects of the present disclosure, in general, the following Examples describe some additional aspects of the present disclosure. While aspects of the present disclosure are described in connection with the following examples and the corresponding text and figures, there is no intent to limit aspects of the present disclosure to this description. On the contrary, the intent is to cover all alternatives, modifications, and equivalents included within the spirit and scope of the present disclosure.AspectsAspect 1. A method for reducing or inhibiting flow in a vessel in a subject comprising introducing into the vessel a viscoelastic polyelectrolyte hydrogel comprising a polycationic polyelectrolyte, a polyanionic polyelectrolyte, and monovalent and / or divalent ions, wherein prior to administration of the polyelectrolyte hydrogel to the subject, the polyelectrolyte hydrogel has an initial elastic modulus greater than the viscous modulus, wherein the initial elastic modulus of the polyelectrolyte hydrogel decreases under shear when administered to the subject, and wherein the recovered elastic modulus of the polyelectrolyte hydrogel in physiological conditions is at least 80% of the initial elastic modulus of the polyelectrolyte hydrogel.Aspect 2. The method of Aspect 1, wherein the polyanionic polyelectrolyte has from 10 mol% to 90 mol% ionized side chains above pH 4.5.Aspect 3. The method of Aspect 1 , wherein the polyanionic polyelectrolyte comprises only anionic charged groups.Aspect 4. The method of Aspect 1, wherein the polycationic polyelectrolyte has from 10 mol% to 90 mol% ionized side chains above pH 4.5.Aspect 5. The method of Aspect 1 , wherein the polycationic polyelectrolyte comprises only cationic charged groups.Aspect 6. The method of Aspect 1, wherein the charge ratio between the polycationic polyelectrolytes and polyanionic polyelectrolytes at pH of about 6 to about 8 is from 6:1 to 1 :6.Aspect 7. The method of Aspect 1, wherein the initial elastic modulus is greater than or equal to 200 Pa.Aspect 8. The method of Aspect 1 , wherein the elastic modulus and viscosity of the polyelectrolyte hydrogel under shear decrease such that the injection force through a catheter is less than 20 Ibf.Aspect 9. The method of Aspect 1 , wherein the molecular weight of the polyanionic polyelectrolyte is from about 20 kDa to about 10,000 kDa.Aspect 10. The method of Aspect 1 , wherein the polyanionic polyelectrolyte comprises multiple molecular weight polymers to create a multimodal molecular weight distribution.Aspect 11. The method of Aspect 1 , wherein the polyanionic polyelectrolyte is linear or branched.Aspect 12. The method of Aspect 1 , wherein the monovalent ions are sodium and chloride ions with a concentration from about 0.10 M to about 2.5M.Aspect 13. The method of any one of Aspects 1-12, wherein the polyelectrolyte hydrogel forms a right- or left-handed coil during delivery through a catheter, needle, or other delivery device.Aspect 14. The method of any one of Aspects 1-13, wherein the method reduces or inhibits blood flow to a tumor, an aneurysm, a varicose vein, a vascular malformation, geniculate artery, uterine fibroids, prostatic artery, hemorrhoids, middle meningeal artery, or a bleeding wound.Aspect 15. The method of any one of Aspects 1-13, wherein the method reinforces the inner wall of a blood vessel in the subject.Aspect 16. The method of any one of Aspects 1-15, wherein the polyelectrolyte hydrogel further comprises a bioactive agent, wherein the bioactive agent is released from the polyelectrolyte hydrogel after administration of the polyelectrolyte hydrogel to the subject.Aspect 17. The method of any one of Aspects 1-16, wherein the polyanionic polyelectrolyte comprises a polyanionic polysaccharide.Aspect 18. The method of Aspect 17, wherein the polyanionic polysaccharide comprises xanthan gum, hyaluronic acid, gellan gum, alginic acid, carrageenan, or any combination thereof.Aspect 19. The method of any one of Aspects 1-16, wherein the polyanionic polyelectrolyte comprises more than two carboxylate, sulfate, sulfonate, borate, boronate, phosphonate, or phosphate groups.Aspect 20. The method of any one of Aspects 1-16, wherein the polyanionic polyelectrolyte comprises a negatively-charged glycosaminoglycan or an acidic protein.Aspect 21. The method of Aspect 20, wherein the negatively-charged glycosaminoglycan comprises chondroitin sulfate, dermatan sulfate, keratin sulfate, or hyaluronic acid.Aspect 22. The method of any one of Aspects 1-16, wherein the polyanionic polyelectrolyte comprises a negatively-charged protein having a net negative charge at a pH of 6 or greater.Aspect 23. The method of any one of Aspects 1-16, wherein the polyanionic polyelectrolyte comprises a negatively-charged polymer comprising anionic groups pendant to the backbone of the polymer, incorporated in the backbone of the polymer backbone, or a combination thereof.Aspect 24. The method of any one of Aspects 1-16, wherein the polyanionic polyelectrolyte comprises a negatively-charged homopolymer or copolymer comprising two or more anionic groups.Aspect 25. The method of any one of Aspects 1-16, wherein the polyanionic polyelectrolyte is a copolymer comprising two or more fragments having the formula XIwherein R4is hydrogen or an alkyl group; n is from 1 to 10;Y is oxygen, sulfur, or NR30, wherein R30is hydrogen, an alkyl group, or an aryl group;Z’ is a pharmaceutically-acceptable salt of an anionic group.Aspect 26. The method of Aspect 25, wherein Z’ is carboxylate, sulfate, sulfonate, borate, boronate, a substituted or unsubstituted phosphate or phosphonate.Aspect 27. The method of Aspect 26, wherein n is 2.Aspect 28. The method of any one of Aspects 1-16, wherein the polyanionic polyelectrolyte comprises xanthan gum.Aspect 29. The method of Aspect 28, wherein the polyanion xanthan gum has a molecular weight from about 100 kDa to about 10,000 kDa.Aspect 30. The method of any one of Aspects 1-16, wherein the polyanionic polyelectrolyte comprises hyaluronic acid.Aspect 31 . The method of Aspect 30, wherein the hyaluronic acid has a molecular weight from about 100 kDa to about 5,000 kDa.Aspect 32. The method of any one of Aspects 1-16, wherein the polyanionic polyelectrolyte comprises polyacrylic acid.Aspect 33. The method of Aspect 32, wherein the polyacrylic acid has a molecular weight from about 100 kDa to about 5,000 kDa.Aspect 34. The method of any one of Aspects 1-33, wherein the polyanionic polyelectrolyte is from about 1 weight percent to about 12 weight percent of the hydrogel.Aspect 35. The method of any one of Aspects 1-34, wherein the polycationic polyelectrolyte comprises a protamine.Aspect 36. The method of any one of Aspects 1-34, wherein the polycationic polyelectrolyte is salmine or clupein.Aspect 37. The method of any one of Aspects 1-34, wherein the polycationic polyelectrolyte is a natural polymer or a synthetic polymer containing two or more guanidinyl sidechains.Aspect 38. The method of any one of Aspects 1-34, wherein the polycationic polyelectrolyte comprises a polyacrylate comprising two or more pendant guanidinyl groups.Aspect 39. The method of any one of Aspects 1-34, wherein the polycationic polyelectrolyte comprises a homopolymer comprising pendant guanidinyl groups.Aspect 40. The method of any one of Aspects 1-34, wherein the polycationic polyelectrolyte comprises a copolymer comprising two or more pendant guanidinyl groups.Aspect 41. The method of any one of Aspects 1-34, wherein the polycationic polyelectrolyte comprises a synthetic polyguanidinyl copolymer comprising an acrylate, methacrylate, acrylamide, or methacrylamide backbone and two or more guanidinyl groups pendant to the backbone.Aspect 42. The method of any one of Aspects 1-34, wherein the polycationic polyelectrolyte comprises a synthetic polyguanidinyl copolymer comprising the polymerization product between a monomer selected from the group consisting of an acrylate, a methacrylate, an acrylamide, a methacrylamide, or any combination thereof and a pharmaceutically-acceptable salt of compound of formula Iwherein R1is hydrogen or an alkyl group, X is oxygen or NR5, where R5is hydrogen or an alkyl group, and m is from 1 to 10.Aspect 43. The method of Aspect 42, wherein the polycationic polyelectrolyte comprises a copolymerization product between the compound of formula I and an acrylate, a methacrylate, an acrylamide, or a methacrylamide,Aspect 44. The method of Aspect 42, wherein the polycationic polyelectrolyte comprises a copolymerization product between the compound of formula I and methacrylamide, N-(2- hydroxypropyl)methacrylamide (HPMA), / V-[3-( / V'-dicarboxymethyl)aminopropyl]methacrylamide (DAMA), / V-(3-aminopropyl)methacrylamide, / V-(1 ,3-dihydroxypropan-2-yl) methacrylamide, N- isopropylmethacrylamide, N-hydroxyethylacrylamide (HEMA), or any combination thereof.Aspect 45. The method of Aspect 42, wherein R1is methyl, X is NH, m is 3.Aspect 46. The method of Aspect 42, wherein the mole ratio of the guanidinyl monomer of formula I to the comonomer is from 1 :20 to 20: 1.Aspect 47. The method of Aspect 42, wherein the polyguanidinyl copolymer has an average molar mass from 1 kDa to 1 ,000 kDa.Aspect 48. The method of any one of Aspects 1-47, wherein the polycationic polyelectrolyte is from about 1.0 weight percent to about 25.0 weight percent of the PE hydrogel.Aspect 49. The method of Aspect 1 , wherein the polyanionic polyelectrolyte is xanthan gum and the polycationic polyelectrolyte is a protamine.Aspect 50. The method of Aspect 49, wherein the protamine is salmine.Aspect 51. The method of Aspect 1 , wherein the polyanionic polyelectrolyte is xanthan gum and the polycationic polyelectrolyte is polyguanidinium methacrylamide (pGPMA).Aspect 52. The method of Aspect 1 , wherein the PE hydrogel comprises two different anionic polysaccharides.Aspect 53. The method of Aspect 52, wherein the anionic polysaccharides comprise xanthan gum and hyaluronic acid.Aspect 54. The method of any one of Aspects 1-53, wherein the monovalent ions are sodium ions, and potassium ions and the divalent ions are magnesium ions and calcium ions.Aspect 55. The method of any one of Aspects 1-53, wherein the monovalent anions are chloride ions.Aspect 56. The method of any one of Aspects 1-53, wherein the total concentration of the monovalent cations and anions in the PE hydrogel is from about 0.1 M to about 2.5 M.Aspect 57. The method of any one of Aspects 1-56, wherein the PE hydrogel further comprises a contrast agent.Aspect 58. The method of Aspect 57, wherein the contrast agent is a radiographic contrast agent.Aspect 59. The method of Aspect 57, wherein the contrast agent is tantalum metal particles, gold particles, or tantalum oxide particles.Aspect 60. The method of Aspect 57, wherein the contrast agent is a transient contrast agent.Aspect 61. The method of Aspect 60, wherein the transient contrast agent comprises an iodinated organic compound.Aspect 62. The method of Aspect 61 , wherein the iodinated organic compound comprises iopamidol, iodixanol, iohexol, iopromide, iobtiridol, iomeprol, iopentol, iopamiron, ioxilan, iotrolan, iotrol and ioversol, iopanoate, diatrizoic acid, iothalamate, ioxaglate, or any combination thereof.Aspect 63. The method of Aspect 61 , wherein the iodinated organic compound comprises an iodinated oil.Aspect 64. The method of any one of Aspects 60-63, wherein the concentration of the transient contrast agent in the PE hydrogel is from 50 mgl / mL to 450 mgl / mL.Aspect 65. The method of any one of Aspects 60-64, wherein the transient contrast agent diffuses out of the polyelectrolyte hydrogel and becomes undetectable in 5 minutes to 30 days.Aspect 66. The method of any one of Aspects 1-65, wherein the polyelectrolyte hydrogel further comprises natural or synthetic fibers, water-insoluble filler particles, a nanoparticle, or a microparticle.Aspect 67. The method of Aspect 66, wherein the fibers comprise a milled and sieved crosslinked gelatin foam fiber.Aspect 68. The method of any one of Aspects 1-67, wherein the polyelectrolyte hydrogel further comprises one or more bioactive agents, wherein the bioactive agent comprises an antibiotic, a pain reliever, an immune modulator, a growth factor, an enzyme inhibitor, a hormone, a messenger molecule, a cell signaling molecule, a receptor agonist, an oncolytic virus, a chemotherapy agent, a receptor antagonist, a nucleic acid, a chemically-modified nucleic acid, or any combination thereof.Aspect 69. The method of any one of Aspects 1-68, wherein the polyelectrolyte hydrogel further comprises a nonionic polysaccharide.Aspect 70. The method of Aspect 69, wherein the nonionic polysaccharide comprises guar gum, locust bean gum, a modified starch, or a combination thereof.Aspect 71. The method of any one of Aspects 1-70, wherein the polyelectrolyte hydrogel further comprises silicate nanoparticles.Aspect 72. A polyelectrolyte hydrogel comprising a polycation, a polyanion, and monovalent ions having an initial elastic modulus greater than the viscous modulus, wherein the initial elastic modulus of the polyelectrolyte hydrogel decreases under shear, and wherein the recovered elastic modulus of the polyelectrolyte hydrogel is at least 80% of the initial elastic modulus of the polyelectrolyte hydrogel in physiological conditions.Aspect 73. The polyelectrolyte hydrogel of Aspect 72, wherein the polyanionic polyelectrolyte has from 10 mol% to 90 mol% ionized side chains above pH 6.Aspect 74. The polyelectrolyte hydrogel of Aspect 72, wherein the polyanionic polyelectrolyte comprises only anionic charged groups.Aspect 75. The polyelectrolyte hydrogel of Aspect 72, wherein the polycationic polyelectrolyte has from 10 mol% to 90 mol% ionized side chains above pH 6.Aspect 76. The polyelectrolyte hydrogel of Aspect 72, wherein the polycationic polyelectrolyte comprises only cationic charged groups.Aspect 77. The polyelectrolyte hydrogel of Aspect 72, wherein the charge ratio between the polycationic polyelectrolytes and polyanionic polyelectrolytes at pH of about 6 to about 8 is from 6:1 to 1:6.Aspect 78. The polyelectrolyte hydrogel of Aspect 72, wherein the initial elastic modulus is greater than or equal to 200 Pa.Aspect 79. The polyelectrolyte hydrogel of Aspect 72, wherein the elastic modulus and viscosity of the polyelectrolyte hydrogel under shear decrease such that the injection force through a catheter is less than 14 Ibf.Aspect 80. The polyelectrolyte hydrogel of Aspect 72, wherein the molecular weight of the polyanionic polyelectrolyte is from about 20 kDa to about 10,000 kDa.Aspect 81. The polyelectrolyte hydrogel of Aspect 72, wherein the polyanionic polyelectrolyte comprises multiple molecular weight polymers to create a multimodal molecular weight distribution.Aspect 82. The polyelectrolyte hydrogel of Aspect 72, wherein the polyanionic polyelectrolyte is linear or branched.Aspect 83. The polyelectrolyte hydrogel of Aspect 72, wherein the monovalent ions are sodium and chloride ions with a concentration from about 0.10 M to about 2.5M.Aspect 84. The polyelectrolyte hydrogel of any one of Aspects 72-83, wherein the polyelectrolyte hydrogel forms a right- or left-handed coil during delivery through a catheter, needle, or other delivery device.Aspect 85. The polyelectrolyte hydrogel of any one of Aspects 72-84, wherein the method reduces or inhibits blood flow to a tumor, an aneurysm, a varicose vein, a vascular malformation, geniculate artery, uterine fibroids, prostatic artery, hemorrhoids, middle meningeal artery, or a bleeding wound.Aspect 86. The polyelectrolyte hydrogel of any one of Aspects 72-84, wherein the method reinforces the inner wall of a blood vessel in the subject.Aspect 87. The polyelectrolyte hydrogel of any one of Aspects 72-84, wherein the polyelectrolyte hydrogel further comprises a bioactive agent, wherein the bioactive agent is released from the polyelectrolyte hydrogel after administration of the polyelectrolyte hydrogel to the subject.Aspect 88. The polyelectrolyte hydrogel of any one of Aspects 72-85, wherein the polyanionic polyelectrolyte comprises a polyanionic polysaccharide.Aspect 89. The polyelectrolyte hydrogel of Aspect 86, wherein the polyanionic polysaccharide comprises xanthan gum, hyaluronic acid, gellan gum, alginic acid, carrageenan, or any combination thereof.Aspect 90. The polyelectrolyte hydrogel of any one of Aspects 72-85, wherein the polyanionic polyelectrolyte comprises more than two carboxylate, sulfate, sulfonate, borate, boronate, phosphonate, or phosphate groups.Aspect 91. The polyelectrolyte hydrogel of any one of Aspects 72-85, wherein the polyanionic polyelectrolyte comprises a negatively-charged glycosaminoglycan or an acidic protein.Aspect 92. The polyelectrolyte hydrogel of Aspect 89, wherein the negatively-charged glycosaminoglycan comprises chondroitin sulfate, dermatan sulfate, keratin sulfate, or hyaluronic acid.Aspect 93. The polyelectrolyte hydrogel of any one of Aspects 72-85, wherein the polyanionic polyelectrolyte comprises a negatively-charged protein having a net negative charge at a pH of 6 or greater.Aspect 94. The polyelectrolyte hydrogel of any one of Aspects 72-85, wherein the polyanionic polyelectrolyte comprises a negatively-charged polymer comprising anionic groups pendant to the backbone of the polymer, incorporated in the backbone of the polymer backbone, or a combination thereof.Aspect 95. The polyelectrolyte hydrogel of any one of Aspects 72-85, wherein the polyanionic polyelectrolyte comprises a negatively-charged homopolymer or copolymer comprising two or more anionic groups.Aspect 96. The polyelectrolyte hydrogel of any one of Aspects 72-85, wherein the polyanionic polyelectrolyte is a copolymer comprising two or more fragments having the formula XIwherein R4is hydrogen or an alkyl group; n is from 1 to 10;Y is oxygen, sulfur, or NR30, wherein R30is hydrogen, an alkyl group, or an aryl group;Z’ is a pharmaceutically-acceptable salt of an anionic group.Aspect 97. The polyelectrolyte hydrogel of Aspect 96, wherein Z’ is carboxylate, sulfate, sulfonate, borate, boronate, a substituted or unsubstituted phosphate or phosphonate.Aspect 98. The polyelectrolyte hydrogel of Aspect 97, wherein n is 2.Aspect 99. The polyelectrolyte hydrogel of any one of Aspects 72-85, wherein the polyanionic polyelectrolyte comprises xanthan gum.Aspect 100. The polyelectrolyte hydrogel of Aspect 99, wherein the polyanion xanthan gum has a molecular weight from about 100 kDa to about 10,000 kDa.Aspect 101. The polyelectrolyte hydrogel of any one of Aspects 72-85, wherein the polyanionic polyelectrolyte comprises hyaluronic acid.Aspect 102. The polyelectrolyte hydrogel of Aspect 101 , wherein the hyaluronic acid has a molecular weight from about 100 kDa to about 5,000 kDa.Aspect 103. The polyelectrolyte hydrogel of any one of Aspects 72-85, wherein the polyanionic polyelectrolyte comprises polyacrylic acid.Aspect 104. The polyelectrolyte hydrogel of Aspect 103, wherein the polyacrylic acid has a molecular weight from about 100 kDa to about 5,000 kDa.Aspect 105. The polyelectrolyte hydrogel of any one of Aspects 72-104, wherein the polyanionic polyelectrolyte is from about 1 weight percent to about 12 weight percent of the hydrogel.Aspect 106. The polyelectrolyte hydrogel of any one of Aspects 72-105, wherein the polycationic polyelectrolyte comprises a protamine.Aspect 107. The polyelectrolyte hydrogel of any one of Aspects 72-105, wherein the polycationic polyelectrolyte is salmine or clupein.Aspect 108. The polyelectrolyte hydrogel of any one of Aspects 72-105, wherein the polycationic polyelectrolyte is a natural polymer or a synthetic polymer containing two or more guanidinyl sidechains.Aspect 109. The polyelectrolyte hydrogel of any one of Aspects 72-105, wherein the polycationic polyelectrolyte comprises a polyacrylate comprising two or more pendant guanidinyl groups.Aspect 110. The polyelectrolyte hydrogel of any one of Aspects 72-105, wherein the polycationic polyelectrolyte comprises a homopolymer comprising pendant guanidinyl groups.Aspect 111. The polyelectrolyte hydrogel of any one of Aspects 72-105, wherein the polycationic polyelectrolyte comprises a copolymer comprising two or more pendant guanidinyl groups.Aspect 112. The polyelectrolyte hydrogel of any one of Aspects 72-105, wherein the polycationic polyelectrolyte comprises a synthetic polyguanidinyl copolymer comprising an acrylate, methacrylate, acrylamide, or methacrylamide backbone and two or more guanidinyl groups pendant to the backbone.Aspect 113. The polyelectrolyte hydrogel of any one of Aspects 72-105, wherein the polycationic polyelectrolyte comprises a synthetic polyguanidinyl copolymer comprising the polymerization product between a monomer selected from the group consisting of an acrylate, a methacrylate, an acrylamide, a methacrylamide, or any combination thereof and a pharmaceutically-acceptable salt of compound of formula Iwherein R1is hydrogen or an alkyl group, X is oxygen or NR5, where R5is hydrogen or an alkyl group, and m is from 1 to 10.Aspect 114. The polyelectrolyte hydrogel of Aspect 113, wherein the polycationic polyelectrolyte comprises a copolymerization product between the compound of formula I and an acrylate, a methacrylate, an acrylamide, or a methacrylamide,Aspect 115. The polyelectrolyte hydrogel of Aspect 113, wherein the polycationic polyelectrolyte comprises a copolymerization product between the compound of formula I and methacrylamide, A / -(2-hydroxypropyl)methacrylamide (HPMA), A / -[3-(A / '- dicarboxymethyl)aminopropyl]methacrylamide (DAMA), / V-(3-aminopropyl)methacrylamide, / V- (1 ,3-dihydroxypropan-2-yl) methacrylamide, N-isopropylmethacrylamide, N- hydroxyethylacrylamide (HEMA), or any combination thereof.Aspect 116. The polyelectrolyte hydrogel of Aspect 113, wherein R1is methyl, X is NH, m is 3.Aspect 117. The polyelectrolyte hydrogel of Aspect 113, wherein the mole ratio of the guanidinyl monomer of formula I to the comonomer is from 1 :20 to 20:1.Aspect 118. The polyelectrolyte hydrogel of Aspect 113, wherein the polyguanidinyl copolymer has an average molar mass from 1 kDa to 1 ,000 kDa.Aspect 119. The polyelectrolyte hydrogel of any one of Aspects 72-118, wherein the polycationic polyelectrolyte is from about 1.0 weight percent to about 25.0 weight percent of the PE hydrogel.Aspect 120. The polyelectrolyte hydrogel of Aspect 72, wherein the polyanionic polyelectrolyte is xanthan gum and the polycationic polyelectrolyte is a protamine.Aspect 121. The polyelectrolyte hydrogel of Aspect 120, wherein the protamine is salmine.Aspect 122. The polyelectrolyte hydrogel of Aspect 72, wherein the polyanionic polyelectrolyte is xanthan gum and the polycationic polyelectrolyte is polyguanidinium methacrylamide (pGPMA).Aspect 123. The polyelectrolyte hydrogel of Aspect 72, wherein the PE hydrogel comprises two different anionic polysaccharides.Aspect 124. The polyelectrolyte hydrogel of Aspect 123, wherein the anionic polysaccharides comprise xanthan gum and hyaluronic acid.Aspect 125. The polyelectrolyte hydrogel of any one of Aspects 72-124, wherein the monovalent cations are sodium ions, potassium ions and the divalent cations are magnesium ions and calcium ions.Aspect 126. The polyelectrolyte hydrogel of any one of Aspects 72-124, wherein the monovalent anions are chloride ions.Aspect 127. The polyelectrolyte hydrogel of any one of Aspects 72-124, wherein the total concentration of the monovalent and / or divalent ions in the PE hydrogel is from about 0.1 M to about 2.5 M.Aspect 128. The polyelectrolyte hydrogel of any one of Aspects 72-127, wherein the polyelectrolyte hydrogel further comprises a contrast agent.Aspect 129. The polyelectrolyte hydrogel of Aspect 128, wherein the contrast agent is a radiographic contrast agent.Aspect 130. The polyelectrolyte hydrogel of Aspect 128, wherein the contrast agent is tantalum metal particles, gold particles, or tantalum oxide particles.Aspect 131. The polyelectrolyte hydrogel of Aspect 128, wherein the contrast agent is a transient contrast agent.Aspect 132. The polyelectrolyte hydrogel of Aspect 131, wherein the transient contrast agent comprises an iodinated organic compound.Aspect 133. The polyelectrolyte hydrogel of Aspect 132, wherein the iodinated organic compound comprises iopamidol, iodixanol, iohexol, iopromide, iobtiridol, iomeprol, iopentol, iopamiron,ioxilan, iotrolan, iotrol and ioversol, iopanoate, diatrizoic acid, iothalamate, ioxaglate, or any combination thereof.Aspect 134. The polyelectrolyte hydrogel of Aspect 132, wherein the iodinated organic compound comprises an iodinated oil.Aspect 135. The polyelectrolyte hydrogel of any one of Aspects 131-134, wherein the concentration of the transient contrast agent in the PE hydrogel is from 50 mgl / mL to 450 mgl / mL.Aspect 136. The polyelectrolyte hydrogel of any one of Aspects 131-135, wherein the transient contrast agent diffuses out of the PE hydrogel and becomes undetectable in 5 minutes to 30 days.Aspect 137. The polyelectrolyte hydrogel of any one of Aspects 72-136, wherein the polyelectrolyte hydrogel further comprises natural or synthetic fibers, water-insoluble filler particles, a nanoparticle, or a microparticle.Aspect 138. The polyelectrolyte hydrogel of Aspect 137, wherein the fibers comprise a milled and sieved crosslinked gelatin foam fiber.Aspect 139. The polyelectrolyte hydrogel of any one of Aspects 72-138, wherein the polyelectrolyte hydrogel further comprises one or more bioactive agents, wherein the bioactive agent comprises an antibiotic, a pain reliever, an immune modulator, a growth factor, an enzyme inhibitor, a hormone, a messenger molecule, a cell signaling molecule, a receptor agonist, an oncolytic virus, a chemotherapy agent, a receptor antagonist, a nucleic acid, a chemically- modified nucleic acid, or any combination thereof.Aspect 140. The polyelectrolyte hydrogel of any one of Aspects 72-139, wherein the polyelectrolyte hydrogel further comprises a nonionic polysaccharide.Aspect 141. The polyelectrolyte hydrogel of Aspect 140, wherein the nonionic polysaccharide comprises guar gum, locust bean gum, a modified starch, or a combination thereof.Aspect 142. The method of any one of Aspects 72-139, wherein the polyelectrolyte hydrogel further comprises silicate nanoparticles.Aspect 143. A kit comprising(a) a first syringe comprising the polyelectrolyte hydrogel in any one of Aspects 72- 142, and(b) instructions for administering the polyelectrolyte hydrogel to a subject.Aspect 144. The kit of Aspect 143, wherein the kit further comprises a second syringe comprising a contrast agent and water or saline.Aspect 145. The kit of Aspect 143 or 144, wherein the kit further comprises a second syringe attached to the first syringe with a female-female luer adapter for mixing of the PE hydrogel prior to useAspect 146. The kit Aspect of 143 or 144, wherein the kit further comprises a second syringe filled with dehydrated or hydrated fibers or gel modifier.Aspect 147. The kit of Aspect of 143 or 144, wherein the kit further comprises an adapter for loading PE hydrogel into the lumen of the catheter or delivery device with minimal contact to the hub of the delivery device.Aspect 148. A polyelectrolyte hydrogel comprising (a) xanthan gum, (b) one or more polycationic polyelectrolytes, and (c) ions comprising monovalent ions, divalent ions, or a combination thereof.Aspect 149. The polyelectrolyte hydrogel of Aspect 148, wherein the polyelectrolyte hydrogel has an initial elastic modulus greater than the viscous modulus, wherein the initial elastic modulus of the polyelectrolyte hydrogel decreases under shear during delivery through a conduit, and wherein the elastic modulus of the polyelectrolyte hydrogel recovers to a sufficient level in physiological conditions to occlude or fill the desired location.Aspect 150. The polyelectrolyte hydrogel of Aspect 148 or 149, wherein the elastic modulus and viscosity of the polyelectrolyte hydrogel under shear decrease such that the injection force through a catheter is less than 20 Ibf.Aspect 151. The polyelectrolyte hydrogel of any one of Aspects 148-150, wherein xanthan gum is from about 1.0 weight percent to about 12 weight percent of the hydrogel.Aspect 152. The polyelectrolyte hydrogel of any one of Aspects 148-151 , wherein xanthan gum has a molecular weight from about 100 kDa to about 10,000 kDa.Aspect 153. The polyelectrolyte hydrogel of any one of Aspects 148-152, wherein the polycationic polyelectrolyte has from 10 mol% to 90 mol% ionized side chains above pH 6.3.Aspect 154. The polyelectrolyte hydrogel of any one of Aspects 148-153, wherein the polycationic polyelectrolyte comprises only cationic charged groups.Aspect 155. The polyelectrolyte hydrogel of any one of Aspects 148-154, wherein the charge ratio between the polycationic polyelectrolytes and xanthan gum at pH of about 4.5 to about 8 is from 6:1 to 1:6.Aspect 156. The polyelectrolyte hydrogel of any one of Aspects 148-155, wherein the initial elastic modulus is greater than or equal to 200 Pa and less than 6,000 Pa.Aspect 157. The polyelectrolyte hydrogel of any one of Aspects 148-156, wherein the polycationic polyelectrolyte is from about 0.70 weight percent to about 15 weight percent of the hydrogel.Aspect 158. The polyelectrolyte hydrogel of any one of Aspects 148-157, wherein the polycationic polyelectrolyte comprises a pharmaceutically acceptable salt of chitosan.Aspect 159. The polyelectrolyte hydrogel of Aspect 158, wherein the pharmaceutically acceptable salt of chitosan is the hydrochloride, glutamate, or acetate salt.Aspect 160. The polyelectrolyte hydrogel of Aspect 158 or 159, wherein chitosan has an average molecular weight from about 10 kDa to about 130 kDa.Aspect 161. The polyelectrolyte hydrogel of any one of Aspects 148-160, wherein chitosan has a degree of deacetylation (DDA) greater than 85%.Aspect 162. The polyelectrolyte hydrogel of any one of Aspects 148-161, wherein the pharmaceutically acceptable salt of chitosan is from about 0.70 weight percent to about 8 weight percent of the hydrogel.Aspect 163. The polyelectrolyte hydrogel of any one of Aspects 148-162, wherein the polycationic polyelectrolyte has from 85 mol% to 100 mol% ionized side chains at a pH of about 4.5 to 6.3.Aspect 164. The polyelectrolyte hydrogel of any one of Aspects 148-157, wherein the polycationic polyelectrolyte comprises a protamine.Aspect 165. The polyelectrolyte hydrogel of any one of Aspects 147-157, wherein the polycationic polyelectrolyte is salmine or clupein.Aspect 166. The polyelectrolyte hydrogel of Aspect 165, wherein the polycationic polyelectrolyte is from about 0.70 weight percent to about 12 weight percent of the hydrogel.Aspect 167. The polyelectrolyte hydrogel of any one of Aspects 148-157, wherein the polycationic polyelectrolyte is a natural polymer or a synthetic polymer containing two or more guanidinyl sidechains.Aspect 168. The polyelectrolyte hydrogel of any one of Aspects 148-157, wherein the polycationic polyelectrolyte comprises a polyacrylate comprising two or more pendant guanidinyl groups.Aspect 169. The polyelectrolyte hydrogel of any one of Aspects 148-157, wherein the polycationic polyelectrolyte comprises a homopolymer comprising pendant guanidinyl groups.Aspect 170. The polyelectrolyte hydrogel of any one of Aspects 148-157, wherein the polycationic polyelectrolyte comprises a copolymer comprising two or more pendant guanidinyl groups.Aspect 171. The polyelectrolyte hydrogel of any one of Aspects 148-157, wherein the polycationic polyelectrolyte comprises a synthetic polyguanidinyl copolymer comprising an acrylate, methacrylate, acrylamide, or methacrylamide backbone and two or more guanidinyl groups pendant to the backbone.Aspect 172. The polyelectrolyte hydrogel of any one of Aspects 148-157, wherein the polycationic polyelectrolyte comprises a synthetic polyguanidinyl copolymer comprising the polymerization product between a monomer selected from the group consisting of an acrylate, a methacrylate, an acrylamide, a methacrylamide, or any combination thereof and a pharmaceutically-acceptable salt of compound of formula Iwherein R1is hydrogen or an alkyl group, X is oxygen or NR5, where R5is hydrogen or an alkyl group, and m is from 1 to 10.Aspect 173. The polyelectrolyte hydrogel of Aspect 172, wherein the polycationic polyelectrolyte comprises a copolymerization product between the compound of formula I and an acrylate, a methacrylate, an acrylamide, or a methacrylamide,Aspect 174. The polyelectrolyte hydrogel of Aspect 172, wherein the polycationic polyelectrolyte comprises a copolymerization product between the compound of formula I and methacrylamide, A / -(2-hydroxypropyl)methacrylamide (HPMA), A / -[3-(A / '- dicarboxymethyl)aminopropyl]methacrylamide (DAMA), A / -(3-aminopropyl)methacrylamide, / V- (1 ,3-dihydroxypropan-2-yl) methacrylamide, N-isopropylmethacrylamide, N- hydroxyethylacrylamide (HEMA), or any combination thereof.Aspect 175. The polyelectrolyte hydrogel of Aspect 172, wherein R1is methyl, X is NH, m is 3.Aspect 176. The polyelectrolyte hydrogel of Aspect 172, wherein the mole ratio of the guanidinyl monomer of formula I to the comonomer is from 1 :20 to 20:1.Aspect 177. The polyelectrolyte hydrogel of Aspect 172, wherein the polyguanidinyl copolymer has an average molar mass from 1 kDa to 1 ,000 kDa.Aspect 178. The polyelectrolyte hydrogel of any one of Aspects 167-177, wherein the polycationic polyelectrolyte is from about 0.70 weight percent to about 12.0 weight percent of the hydrogel.Aspect 179. The polyelectrolyte hydrogel of any one of Aspects 148-178, wherein the ions comprise sodium ions, potassium ions, calcium ions, magnesium ions, or any combination thereof and chloride ions.Aspect 180. The polyelectrolyte hydrogel of any one of Aspects 148-179, wherein the total concentration of the ions in the polyelectrolyte hydrogel is from about 0.1 M to about 2.5 M.Aspect 181. The polyelectrolyte hydrogel of any one of Aspects 148-180, wherein the ions comprise calcium ions and chloride ions, wherein the total concentration of the ions in the polyelectrolyte hydrogel is from about 0.10 M to about 2.50 M.Aspect 182. The polyelectrolyte hydrogel of any one of Aspects 148-181 , wherein the ions comprise sodium ions and chloride ions, wherein the total concentration of the ions in the polyelectrolyte hydrogel is from about 0.10 M to about 2.50 M.Aspect 183. The polyelectrolyte hydrogel of any one of Aspects 148-180, wherein the ions comprise potassium ions and chloride ions, wherein the total concentration of the ions in the polyelectrolyte hydrogel is from about 0.10 M to about 2.50 M.Aspect 184. The polyelectrolyte hydrogel of any one of Aspects 148-180, wherein the ions comprise magnesium ions and chloride ions, wherein the total concentration of the ions in the polyelectrolyte hydrogel is from about 0.10 M to about 2.50 M.Aspect 185. The polyelectrolyte hydrogel of any one of Aspects 148-184, wherein the polyelectrolyte hydrogel further comprises a contrast agent.Aspect 186. The polyelectrolyte hydrogel of Aspect 185, wherein the contrast agent is a radiographic contrast agent.Aspect 187. The polyelectrolyte hydrogel of Aspect 185, wherein the contrast agent is tantalum metal particles, gold particles, or tantalum oxide particles.Aspect 188. The polyelectrolyte hydrogel of Aspect 185, wherein the contrast agent is a transient contrast agent.Aspect 189. The polyelectrolyte hydrogel of Aspect 188, wherein the transient contrast agent comprises an iodinated organic compound.Aspect 190. The polyelectrolyte hydrogel of Aspect 189, wherein the iodinated organic compound comprises iopamidol, iodixanol, iohexol, iopromide, iobtiridol, iomeprol, iopentol, iopamiron, ioxilan, iotrolan, iotrol and ioversol, iopanoate, diatrizoic acid, iothalamate, ioxaglate, or any combination thereof.Aspect 191. The polyelectrolyte hydrogel of Aspect 189, wherein the iodinated organic compound comprises an iodinated oil.Aspect 192. The polyelectrolyte hydrogel of any one of Aspects 185-191 , wherein the contrast agent is up to 40 weight percent of the polyelectrolyte hydrogel.Aspect 193. The polyelectrolyte hydrogel of any one of Aspects 148-192, wherein the polyelectrolyte hydrogel further comprises natural or synthetic fibers, water-insoluble filler particles, a nanoparticle, or a microparticle.Aspect 194. The polyelectrolyte hydrogel of Aspect 193, wherein the fibers comprise crosslinked gelatin foam fibers.Aspect 195. The polyelectrolyte hydrogel of Aspect 193, wherein the fibers comprise Type A crosslinked gelatin foam fibers or Type A crosslinked gelatin foam fibers.Aspect 196. The polyelectrolyte hydrogel of Aspect 194 or 195, wherein the fibers are from 0.1 weight percent to 5 weight percent of the polyelectrolyte hydrogel.Aspect 197. The polyelectrolyte hydrogel of any one of Aspects 148-196, wherein the polyelectrolyte hydrogel further comprises a bioactive agent.Aspect 198. The polyelectrolyte hydrogel of Aspect 197, wherein the bioactive agent comprises an antibiotic, a pain reliever, an immune modulator, a growth factor, an enzyme inhibitor, a hormone, a messenger molecule, a cell signaling molecule, a receptor agonist, an oncolytic virus, a chemotherapy agent, a receptor antagonist, a nucleic acid, a chemically-modified nucleic acid, or any combination thereof.Aspect 199. The polyelectrolyte hydrogel of any one of Aspects 148-198, wherein the polyelectrolyte hydrogel further comprises a nonionic polysaccharide.Aspect 200. The polyelectrolyte hydrogel of Aspect 199, wherein the nonionic polysaccharide comprises guar gum, locust bean gum, a modified starch, or a combination thereof.Aspect 201. The polyelectrolyte hydrogel of any one of Aspects 148-200, wherein the polyelectrolyte hydrogel further comprises silicate nanoparticles.Aspect 202. A polyelectrolyte hydrogel comprising (a) a pharmaceutically acceptable salt of chitosan, a polyguanidinyl copolymer, a protamine, or any combination thereof (b) a polyanionic polyelectrolyte, and (c) ions comprising monovalent ions, divalent ions, or a combination thereof.Aspect 203. The polyelectrolyte hydrogel of Aspect 202, wherein the polyelectrolyte hydrogel has an initial elastic modulus greater than the viscous modulus, wherein the initial elastic modulus of the polyelectrolyte hydrogel decreases under shear during delivery through a conduit, and wherein the elastic modulus of the polyelectrolyte hydrogel recovers to a sufficient level in physiological conditions to occlude or fill the desired location.Aspect 204. The polyelectrolyte hydrogel of Aspect 202 or 203, wherein the elastic modulus and viscosity of the polyelectrolyte hydrogel under shear decrease such that the injection force through a catheter is less than 20 Ibf.Aspect 205. The polyelectrolyte hydrogel of any one of Aspects 202-204, wherein the polyanionic polyelectrolyte comprises a polyanionic polysaccharide.Aspect 206. The polyelectrolyte hydrogel of Aspect 205, wherein the polyanionic polysaccharide comprises xanthan gum, hyaluronic acid, gellan gum, alginic acid, carrageenan, or any combination thereof.Aspect 207. The polyelectrolyte hydrogel of Aspect 205, wherein the polyanionic polyelectrolyte comprises a negatively-charged glycosaminoglycan or an acidic protein.Aspect 208. The polyelectrolyte hydrogel of Aspect 207, wherein the negatively-charged glycosaminoglycan comprises chondroitin sulfate, dermatan sulfate, keratin sulfate, or hyaluronic acid.Aspect 209. The polyelectrolyte hydrogel of any one of Aspects 202-204, wherein the polyanionic polyelectrolyte comprises xanthan gum.Aspect 210. The polyelectrolyte hydrogel of Aspect 209, wherein xanthan gum is from about 1.0 weight percent to about 12 weight percent of the hydrogel.Aspect 211. The polyelectrolyte hydrogel of Aspect 209 or 210, wherein xanthan gum has a molecular weight from about 100 kDa to about 10,000 kDa.Aspect 212. The polyelectrolyte hydrogel of Aspects 148-211 , wherein the elastic modulus and the viscosity of the polyelectrolyte hydrogel continue to increase after delivery into physiological media.Aspect 213. The polyelectrolyte hydrogel of Aspect 212, wherein the elastic modulus of the polyelectrolyte hydrogel after 30 minutes in physiological media is between 600 Pa and 25,000 Pa.Aspect 214. The polyelectrolyte hydrogel of Aspect 212 or 213, wherein the elastic modulus of the polyelectrolyte hydrogel remains greater than the viscous modulus.Aspect 215. The polyelectrolyte hydrogel of Aspects 148-214, wherein the polyelectrolyte hydrogel is exposed to a liquid with ionic content less than the polyelectrolyte hydrogel to increase the elastic modulus prior to delivery.Aspect 216. The polyelectrolyte hydrogel of Aspect 215, wherein the elastic modulus continues to increase after delivery into physiological mediaAspect 217. The polyelectrolyte hydrogel of Aspect 215, wherein, the elastic modulus after delivery into physiological media, remains within ±10% of the initial elastic modulus prior to delivery.Aspect 218. A method for reducing or inhibiting flow in a vessel in a subject comprising introducing into the vessel the polyelectrolyte hydrogel of any one of Aspects 148-217.Aspect 219. The method of Aspect 218, wherein the method reduces or inhibits blood flow to a tumor, an aneurysm, an endoleak, a varicose vein, a varicocele, a gonadal vein, an ovarian vein, a pelvic vein, a gastrointestinal artery, a rectal artery, a mesenteric artery, the gastroduodenal artery, hepatic artery, the splenic artery, an iliac artery, the portal vein, a vascular malformation, geniculate artery, uterine fibroids, prostatic artery, hemorrhoids, middle meningeal artery, or a bleeding wound.Aspect 220. The method of Aspect 219, wherein the method reinforces the inner wall of a blood vessel in the subject.Aspect 221. The method of Aspect 219, wherein the method temporarily reduces blood flow.Aspect 222. The method of Aspect 221, wherein the method temporarily reduces blood flow in musculoskeletal regions.Aspect 223. A method for filling a void in a subject comprising introducing into the void the polyelectrolyte hydrogel of any one of Aspects 148-217.Aspect 224. The method of Aspect 223, wherein the void is within a bone, muscle, skin, cartilage, tissue, or organ or the void is a pouch or sac attached to a bone, muscle, skin, cartilage, tissue, or organ in the subject.Aspect 225. The method of Aspect 223, wherein the void is a left atrial appendage.Aspect 226. The method of Aspect 223, wherein the void is in a lymph node.Aspect 227. The method of any one of Aspects 223-226, wherein the composition is introduced into the void by a catheter or needle.Aspect 228. The method of any one of Aspects 223-227, wherein the polyelectrolyte hydrogel is first introduced into the subject by a delivery system followed by introducing a low viscosity liquid,a hydrophobic liquid, an aqueous contrast agent, or any combination thereof into the subject by a syringe, wherein the syringe is connected to the delivery system.Aspect 229. The method of Aspect 228, wherein the delivery system comprises a housing having a first end and a second end, an interior chamber within the housing for containing the polyelectrolyte hydrogel, a first Luer connection at the first end of the housing, and a second Luer connection at the second end of the housing; and a needle or catheter attached to the first Luer connection or the second Luer connection, wherein the first and second Luer connection not attached to the needle or catheter can receive the syringe comprising the low viscosity liquid, a hydrophobic liquid, an aqueous contrast agent, or any combination thereof.Aspect 230. The method of Aspect 228 or 229, wherein the low viscosity fluid is saline, a nonionic iodinated contrast agent, dextrose, or sterile water for injection.Aspect 231 . The method of Aspect 228 or 229, wherein the low viscosity fluid also contains lidocaine, nitroglycerin, or verapamil.Aspect 232. The method of Aspect 228 or 229, wherein the hydrophobic liquid comprises ethiodized oil (Lipiodol), a plant-derived oil, or a silicone.Aspect 233. The method of Aspect 228 or 229, wherein the polyelectrolyte hydrogel is used in combination with one or more coils, plugs, liquid embolics, or gelatin foam.Aspect 234. A kit comprising a delivery system for delivering the polyelectrolyte hydrogel of any one of Aspects 148-217; the polyelectrolyte hydrogel; and instructions for administering the polyelectrolyte hydrogel to a subject.Aspect 235. A kit comprising a delivery system comprising the polyelectrolyte hydrogel of any one of Aspects 148-217 contained within the delivery system; and instructions for administering the polyelectrolyte hydrogel to a subject.Aspect 236. The kit of Aspect 234 or 235, wherein the kit further comprises a syringe comprising a low viscosity liquid, a hydrophobic liquid, an aqueous contrast agent, or any combination thereof.Aspect 237. The kit Aspect of 234 or 235, wherein the kit further comprises a syringe filled with dehydrated or hydrated fibers or gel modifier.EXAMPLES

[0200] The following examples are put forth so as to provide those of ordinary skill in the art with a complete disclosure and description of how the compounds, compositions, articles, devices and / or methods claimed herein are made and evaluated, and are intended to be purely exemplary of the disclosure and are not intended to limit the scope of what the inventors regard as their disclosure. Efforts have been made to ensure accuracy with respect to numbers (e.g., amounts, temperature, etc.), but some errors and deviations should be accounted for. Unless indicated otherwise, parts are parts by weight, temperature is in °C or is at ambient temperature, and pressure.

[0201] MATERIALS AND METHODS

[0202] Materials

[0203] Multiple formulations of shear thinning PE hydrogels made from the polycations Protamine sulfate, polyguanidinium methacrylamide (pGPMA), and Chitosan hydrochloride and anionic polysaccharides and methods for manufacture are described herein. Protamine sulfate (salmine) was purchased from MP Biomedical. Xanthan gum from xanthomonas campestris (product No. G1253), i-carageenan (type II commercial grade), sulfated kappa-carageenan, guar gum, and alginic acid sodium salt (medium viscosity) were purchased from Sigma Aldrich. USP grade sodium chloride was purchased from Sigma Aldrich. Type-A porcine skin gelatin was purchased from Sigma-Aldrich and crosslinked gelatin foam fibers of the brand SURGIFOAM® manufactured by Ethicon were purchased from eSutures. Low and High Acyl Gellan gum was purchased from Modernist Pantry. Calcium chloride, magnesium chloride, and potassium chloride were purchased from Sigma Aldrich. Chitosan hydrochloride was purchased from Glentham Life Science Ltd.

[0204] Method 1

[0205] Stock solutions of the primary polycations (protamine sulfate, pGPMA, chitosan) and polyanions (xanthan gum, sodium hyaluronate) were prepared prior to mixing. For all stock solutions, endotoxin free deionized water (Fisher-Scientific) was used. A 10% solution of protamine sulfate was made by heating deionized water (pH 5.5-7) up to 60 °C and then adding protamine powder gradually while vortexing for 1-5 min. The mixture was then placed into a heated water bath of 50-60 °C until protamine fully dissolved. The heated 10% protamine solution was clear and at lower temperatures became cloudy. Stock solutions of 8-12% xanthan gum were prepared by adding xanthan gum to deionized water while vortexing. After vortexing, an I KA paddle mixer was used to finish blending the stock solution using a teflon paddle. A stock solution of 5M saline was prepared by adding sodium chloride to deionized water in a glass container and shaking to allow the salt to dissolve. Sodium hydroxide was added to the saline solution to adjust the pH as desired (target 7.0-7.4). Stock solutions of 20% pGPMA were prepared by pH adjusting endotoxin free water with NaOH to 7.0-7.4 and then dissolving lyophilized pGPMA powder prepared according to the procedure provided in US Patent No. 9,913,927B2, which is incorporated by reference for the preparation of pGPMA, in room temperature deionized water and vortexing for 1-2 minutes. Stock solutions of chitosan should be adjusted to an acidic pH <2 with hydrochloric acid.

[0206] Ratios of components were combined to create compositions ranging from 3 to 12% by weight in PE solids. In general, the desired salt content of the composition was selected, and the appropriate amount of 5 M saline added to deionized water in a 50 mL centrifuge tube to yield the appropriate salt content. Next, calculations to determine the ratio of positive to negative charges were performed and the appropriate amount of polycation stock solution added to the saline solution. Light shaking was performed to fully disperse the polycation.

[0207] Next, the polyanion stock solution was gradually added to the saline-polycation solution while vortexing. Initially, the vortex setting was set to 5 so that the low viscosity polycation solution did not overflow and the intensity of the vortexer was increased to 9 as the polyanion was added and the mixture started to gel. The mixtures were vortexed for 5 minutes after which they were inspected for homogeneity. If additional mixing was necessary, rotary paddle mixing was performed at 1000-1400 rpm until the mixture appeared to be a homogeneous gel. Higher salt concentrations form a homogeneous PE hydrogel faster and appear transparent whereas lower salt concentrations <0.75M take longer to mix and have a white appearance (yellow in the case of Alginate). After all mixing operations were complete, the mixtures were centrifuged at 3000 rpm for 15 min to remove air bubbles introduced during the mixing processes.

[0208] Exemplary formulations are provided in the tables below.The salt concentrations for protamine and pGPMA include the counterion salts from the polymers, the salt concentrations listed for the chitosan formulations are only the amount of added salt.The working ranges of each of the primary components are summarized in the table below.

[0209] Methods for formulations containing more than one polycation, one polyanion, and chloride salts.

[0210] Guar Gum and Calcium chloride

[0211] Guar gum powder and calcium chloride of the desired weight were added to the protamine- saline solution to allow it to hydrate fully prior to adding xanthan gum. Mixing and centrifuging proceeded according to method 1.

[0212] Gellan Gum, l-Carageenan, K-Caraqeenan

[0213] If used as secondary additives, these were added as powders to the polycationic-saline solution and heated to above 90 °C for 5 minutes. As the mixture cooled, the primary anionic polysaccharide (e.g., xanthan gum) was added from stock solution under vigorous vortexing. Mixing was done with the IKA overhead paddle mixer and PTFE mixing paddle at 1000-1400 rpm and then centrifuged to remove air bubbles. The addition of gellan gum, l-carageenan, and K- carageenan increased the elastic modulus of xanthan-based gels. Prior to in vivo administration, endotoxins should be removed from anionic polysaccharides using a method such as that in US Patent No. 6,451,772B1. Stock solutions can then be made from purified materials as described.

[0214] Fibers

[0215] Mixture proceeded according to method 1 and prior to centrifuging, fibers, such as crosslinked gelatin fibers were gradually added while vortexing and then any clumps removed through paddle mixing, varying the speed as needed between 400-1400rpm to remove any clumps and attempting to minimize air bubble formation. The mixture was then centrifuged at 4000 rpm at 4°C for 5 minutes to remove all bubbles.

[0216] Alternatively, the fibers can be added to the cationic-saline mixture prior to combination with xanthan gum. This method removes the tendency of the fibers to clump but increases the time for the PE hydrogel to become homogeneous.

[0217] Tantalum or iodinated contrast agent

[0218] Tantalum or iodinated contrast was added after full formation of the PE hydrogel and after all additives had been fully mixed. Adding contrast agent to the protamine-saline solution is possible, however it can mask a lack of homogeneity in the PE hydrogel and it is preferred to add last and mix in with vortexer, paddle mixer or IKA Ultra-Turrax Tube Drive.

[0219] Chitosan

[0220] Powders of chitosan hydrochloride, desired salt(s), xanthan gum, and gelatin fibers (if desired) and contrast agent (if desired) were combined and mixed together vigorously on the highest vortex setting. Next, the powders were added to an appropriate volume of endotoxin-free water and vortexed vigorously for 3-5 minutes until no clumps were visible and the resulting gel appeared to be homogeneous. The PE hydrogel was allowed to sit and continue hydrating for IQ- 20 minutes, after which, it was vortexed for 1-2 more minutes. The PE hydrogel was back-loaded into 10mL syringes using a stainless steel spatula and then transferred into 1mL syringes for autoclave sterilization.

[0221] In the case of unmodified chitosan, the same procedure as above was followed, except that the unmodified chitosan was first dissolved in 1% HCI, pH adjusted to about 5.5 with sodium hydroxide or potassium hydroxide, and then the other powders added to it and mixed as above.

[0222] Gel characterization

[0223] Gels were loaded into syringes and deployed through luer lock dispensing tips into solutions of balanced salt solution (BSS), 0.9% saline, water, and blood to assess the cohesion of the mixture under physiological conditions. PE hydrogels that did not swell and remained intact for >1week in BSS at room and 37°C were considered viable candidates for PE hydrogel embolics. The lowest concentration of PE solids that remained intact was 3% at a 1 :1 charge ratio.

[0224] Injection Force

[0225] To measure injection force, the polyelectrolyte PE hydrogel was first added to 1 mL syringes (Merit Medallion PC 1 mL syringes). Injection was performed through a catheter with inner diameter 0.0235” and length 120 cm at 1 ml_ per minute with a Harvard Apparatus PHD Ultra Syringe Infusion Pump with a Load Star iLoad mini load cell attached to a computer via serial USB port. The data logging was performed using LoadVue LV-1000 software.

[0226] Rheometry

[0227] All rheometry experiments were performed on TA Instruments AR-2000EX Rheometer with Peltier Plate Temperature Control System and TA Instruments RHEOLOGY ADVANTAGE software with a 20mm diameter plate and 500 pm -1000 pm gap with a moisture capture cap and deionized water droplets to prevent drying.

[0228] Temperature Stability Temperature Sweep

[0229] Prior to initiating the testing, the temperature was equilibrated and a 30 second conditioning step was performed prior to testing to ensure equilibration. The temperature ramp stepped from 20-45 °C in 1 °C increments at 1% strain and 1 Hz frequency. The delay time between each measurement was 10 seconds.

[0230] Strain Sweep

[0231] Prior to initiating the testing, the temperature was set to 37 °C and a 60 second conditioning step was performed prior to testing to ensure equilibration. The strain sweep was performed at 1 Hz frequency with strains ranging from 0.01 % to 1000% on a log scale with 5 points per decade. The delay time between each measurement was 6 seconds.

[0232] Frequency Sweep

[0233] Prior to initiating the testing, the temperature was set to 37°C and a 60 second conditioning step was performed prior to testing to ensure equilibration. The frequency sweep was performed at 1% strain with frequencies ranging from 0.1 Hz to 100 Hz on a log scale with 5 points per decade. The delay time between each measurement was 6 seconds.

[0234] Yield Stress

[0235] Prior to initiating the testing, the temperature was set to 37 °C and a 2:00 minute conditioning step with pre-shear stress of 6.4 Pa (10.0 N m torque) was performed prior to testing to ensure equilibration. The yield stress was determined using a stepped flow routine with shear rates ranging from 1.00E-3 to 1.00E3 with 10 points per decade. The constant time parameter was set to 00:05 seconds and each data point was the average of the last two seconds. Shear stress (Pa) was then plotted against shear rate (1 / s) and the yield stress point determined by calculating the point at which there was about a 5% departure from initial linearity.

[0236] Viscosity

[0237] A 20mm diameter plate was used with a 500 pm gap. Prior to initiating the testing, the temperature was set to 37 °C and a 2:00 minute conditioning step with pre-shear stress of 6.4 Pa (10.0 N m torque) was performed prior to testing to ensure equilibration. The viscosity at a range of shear rates was determined using a stepped flow routine with shear rates ranging from 1.00E- 3 to 1.00E3 with 10 points per decade. The constant time parameter was set to 00:05 secondsand each data point was the average of the last two seconds. Viscosity was then plotted against shear rate (1 / s) and the peak viscosity and viscosity at 100 / s shear rate calculated.

[0238] Strain Recovery

[0239] Prior to initiating the testing, the temperature was set to 37 °C and a 2:00 minute conditioning step performed to ensure equilibration. The elastic modulus G’ at high (100%) strain, 1 Hz frequency was sampled 10 times over a 1 minute period and then at low (1%) strain, 1 Hz frequency, for 1 minute repeated up to 3 times. A fast strain recovery is important during procedures where after high deformation during delivery the PE hydrogel properties need to return to the pre-delivery state as quickly as possible after exiting the tip of the catheter.

[0240] pH

[0241] pH can affect the strength of the charges on components of the PE hydrogels as well as stability of components over time. Protamine and pGPMA have a pKa of approximately 13 and will be fully positively charged at nearly all pH ranges. Xanthan has a pka of about 4.5 and will only be negatively charged above 4.5. Chitosan and its derivatives are positively charged and soluble below about pH 6.3 with some charge and partial solubility noted up to pH 6.4. The pH was measured using an InLab pH electrode from Mettler Toledo.

[0242] Gel strength after delivery

[0243] To assess the strength of the formulations after delivery in balanced salt solution representative of the ionic content of blood or blood itself, the following procedure was followed. Approximately 0.30 mL material was deployed into a plastic mold with diameter 20 mm and depth 1.0 mm. The material was spread around the mold to create an even layer of gel. Then the mold and material were submerged into a solution of BSS or blood for 30 minutes. After the incubation period, the sample was removed from the mold and placed on the rheometer measurement stand and G’ measured according to the frequency sweep, temperature sweep, viscosity, and strain sweep procedures described herein. The gap was adjusted to 0.80-1 0mm such that the material was in contact with the base plate and rheometer spindle and the normal force did not exceed 1 N.

[0244] Simulated Use In Vitro Occlusion Models

[0245] Static pressure model

[0246] A 10” long 0.071” (1.8 mm) ID inner diameter male to male luer connector (Qosina 33019) was connected to a hemostasis valve. The hemostasis valve was then connected to a 2-way stop cock and tubing connected to the bottom of 2-5 ft column of water equivalent to 44.8-112.1 mmHg. On the distal end of the male-male tubing a dispensing tip (Jensen Global) was attached with inner diameters ranging from 0.012” (304 pm) to 0.026” (660 pm). A microcatheter of inner diameter 0.0235” or 0.027” was used to deploy 0.1 - 0.3 mL of material into the vessel with water flowing at a pressure of approximately 90 mmHg. The material was then watched for up to 24 hours to assess the ability to plug the distal 304-660 pm tube as well as the proximal 1.8 mm tube by removing the dispensing tip to see if the embolic lodged more proximally was able to occlude flow. The time point at which the occlusion failed was noted. The tube was placed in a heated 37 °C water bath for the duration of testing. All compositions containing 9% solids and PX5M 1.5 were able to occlude a 550 pm taper at 89 mmHg for at least 10 min. PX5M1_2+, PX5M1 , and PX5M.5 plugged a 304 pm simulated vessel for over 24 hours. Under the pressure range tested (40-112 mmHg), the smooth delivery and complete occlusion of flow in a 550 pm simulated vessel was superior to PVA particles 500-700 pm (Cook medical) and 2.5 mm gelatin foam (Embocube Merit Medical).

[0247] Pumped flow model

[0248] A Cole Parmer Masterflex peristaltic pump was used to create an in vitro vascular model of occlusion efficacy. The pump tubing was attached to an in-line pressure gauge and then to various models simulating vascular anatomy. In the simplest example, distal to the pressure gauge, a tuohy-borst hemostasis valve (qosina). was connected to a y-bifurcating luer lock valve was and two lengths of luer connector tubing connected. T o the ends of the luer connecter tubing, dispensing tips (Jensen Global) of various inner diameters and taper geometries were attached to quantitatively assess the size of vessel occlusion possible under various pressure and flow situations. Through the port on the hemostasis valve a model catheter was fed advanced into the desired bifurcation and used to inject embolic. No more than 0.45m L of embolic was ever injected to account for the dead volume in a catheter during most common procedures.

[0249] A second pumped flow model was created by 3D printing a transparent model of a human kidney (See FIG 25B). This model better simulates the more complex flow patterns that occur in the body during embolization and testing was conducted at higher flow rates than in the other models to simulate the effects of delivery in higher flow vessels. As before, a hemostasis valve was connected in-line with the tubing carrying the flow of fluid from the pump and a catheteradvanced to a desired delivery location. The qualitative behavior of the gels was assessed after deploying through a catheter into the model and the peak flow rates and pressures achieved measured.

[0250] RESULTS

[0251] Example 1 : Effect of charge ratio on protamine - xanthan PE hydrogel embolic

[0252] The charge ratio of polyelectrolytes in a PE hydrogel embolic can be adjusted to modify desired properties. At a 1 :1 charge ratio between protamine and xanthan gum, the PE hydrogel was the most durable in balanced salt solution kept at 37 °C. The 1 :4 net negative charged PE hydrogel embolic dissolved faster in a balanced salt solution kept at 37 °C than the 1 :1 and 2:1 examples and will have a faster resorption time in vivo which can be desirable in some applications.

[0253] At a 1+:4' charge ratio, the viscosity and injection force increased (FIG 1A, 1 B), whereas at a 2:1 charge ratio the injection force decreased. The viscosity was measured at a range of shear rates, where the ideal PE hydrogel embolic has a high viscosity at shear rates less than 0.01 but very low viscosities at higher rates of shear between 100-500 / s. This is indicative of PE hydrogels that can provide a mechanical barrier to flow but can be easily delivered to the target location. The decreased injection force of the 2:1 composition makes sense because there are more of the smaller protamine molecules relative to the large xanthan molecules.

[0254] All concepts displayed temperature stability and a net negative charge was found to increase the elastic modulus of the PE hydrogel (G’) (FIG 1 C, 1 D) because more of the large, branched xanthan molecules are present relative to the smaller polycation. The recovery of the PE hydrogels after being strained to 100% strain was consistent across charge ratios, with the magnitude of reduction and recovery being the highest for the net negative 1 :4 ratio gel.

[0255] A higher positive to negative charge ratio may be desirable for some embolization applications because the blood vessel endothelium has a net negative charge due to the presence of negatively charges molecules such as glycosaminoglycans. A net positive charge on the embolic allows the PE hydrogel embolic to anchor to the net negatively charged vessel wall and prevent migration distally.

[0256] Example 2: Effect of sodium chloride molarity on protamine - xanthan PE hydrogel embolics

[0257] The effect of varying the molarity of added monovalent ions was investigated by creating PE hydrogels with a fixed PE solids weight of 5% and 9% comprising protamine sulfate and xanthan gum at a 1 :1 charge ratio. This resulted in formulations of approximately 1.5% protamine sulfate and 3.5% xanthan gum. Sodium chloride was added to bring the added sodium chloride molarity up to 0.50 molar, 1.0 molar, and 1.5 molar. This resulted in total monovalent positive ion molarities of 0.57, 1.07, and 1.57 due to the monovalent ion content of xanthan. The addition of salt resulted in PE hydrogels with a higher overall viscosity and increased injection force through a 0.0235” inner diameter catheter of length 130 cm (FIG 2A, 2B). The increased salt molarity also resulted in a higher elastic modulus that was stable at 20 °C and 37 °C (FIG 2C). The higher salt compositions saw a greater magnitude in the recovery of G’ after 100% strain, but all compositions consistently recovered to greater than 90% of the measured peak G’ within 10 seconds of reducing the strain to 1% (FIG 2D).

[0258] At all three sodium chloride concentrations a stable freestanding PE hydrogel was formed. The lowest concentration of sodium chloride, 0.50 molar, was white in appearance (FIG 3A) and required the most time and mixing to fully form a gel. Increasing the salt content, increased the transparency of the PE hydrogel and reduced the time for a homogeneous PE hydrogel to form (FIG 3B, 3C).

[0259] Example 3: Effect of PE solids content on protamine-xanthan PE hydrogel embolics

[0260] Gel embolic formulations of 5%, 7.5%, and 9% solids were made with 1.0 molar added sodium chloride and a 1 :1 charge ratio between xanthan and protamine. Viscosity was much higher in the 9% group than the 5% group and a roughly linear increase in injection force from a 1mL Merit Medallion syringe through a 0.0235” inner diameter catheter of length 130 cm was seen for increasing the polyelectrolyte concentration. Generally, injection force values under 14 Ibf are considered ergonomically acceptable, therefore the higher percent polyelectrolyte versions at 1.0 molar added sodium chloride would be better suited for larger catheters. Building on the results of Example 2, a combination of reduced salt and higher polyelectrolyte concentrations can be used to create a PE hydrogel with a suitable balance of PE hydrogel strength and injectability.

[0261] The elastic modulus G’ was stable at 20 °C and 37 °C for all percent weights of PE solids with a predictable increase in G’ with increase in the polyelectrolyte concentration (FIG 4G). The higher polyelectrolyte concentration compositions saw a greater magnitude in the recovery of G’ after 100% strain, but all compositions consistently recovered to greater than 90% of the measured peak G’ within 10 seconds of reducing the strain to 1 %.

[0262] Example 4: Effect of sodium chloride molarity on pGPMA-xanthan PE hydrogel embolic material

[0263] Compositions of 5% PE hydrogels comprised of poly(guanidinyl-propyl-methacrylamide) (pGPMA) and xanthan at a 1:1 charge ratio with 0.5, 1.0, and 1.5 molar added sodium chloride were made. The 0.5 molar version did not result in a homogeneous PE hydrogel and was excluded from testing. At least 0.75 molar of added sodium chloride at a 5% weight PE solids was required to form a gel. However, at a higher polyelectrolyte concentration of 12%, a homogeneous, white PE hydrogel was formed with 0.5 molar added sodium chloride. This is due to the increased salt contribution from pGPMA and xanthan at the higher concentration, which helps shield the oppositely charged polymers and create a homogeneous gel. Like polyelectrolyte PE hydrogels comprised of protamine and xanthan, increasing the sodium chloride concentration increased the viscosity (FIG 5A), the injection force through a 130 cm length 0.027” inner diameter catheter (FIG 5B), the G’ at 20 °C and 37 °C (FIG 5C), and the magnitude of recovery after repeated series of 100% strain (FIG 5D). Reducing the salt content from 1.0 molar to 0.5 molar in the 12% solids version reduced the injection force at a rate of 1mL / min from an average of 18.8 Ibf to 10.4 Ibf which is in an acceptable range and shows the tunability of the composition.

[0264] The pGPMA has the advantage of being a synthetic polycation which can be manufactured to tune the molecular weight and other properties to create the desired characteristics of lower injection force and higher PE hydrogel strength.

[0265] Example 5: Effect of polyelectrolyte concentration on pGPMA-xanthan PE hydrogel material

[0266] Polyelectrolyte hydrogel embolic formulations of 5%, 7.0%, and 12% solids were made with 1.0 molar added sodium chloride and a 1 :1 charge ratio between xanthan and pGPMA. Viscosity was much higher in the 12% group than the 5% and 7% group and a roughly linear increase in injection force from a 1mL Merit Medallion syringe through a 0.027” inner diameter catheter of length 130 cm was seen for increasing the polyelectrolyte concentration (FIG 6A, 6B). The 5% and 7% solids concentrations had acceptable levels of injection force for this catheter. The elastic modulus at 20 °C and 37 °C was stable and higher with a higher polyelectrolyte concentration (FIG 6C). The higher polyelectrolyte concentration compositions saw a greater magnitude in the recovery of G’ after 100% strain, but all compositions consistently recovered to greater than 90% of the measured peak G’ within 10 seconds of reducing the strain to 1 %.

[0267] Building on the results of Example 2, a combination of reduced salt and higher polyelectrolyte concentrations can be used to create a PE hydrogel with a suitable balance of PE hydrogel strength and injectability.

[0268] Example 6: Effect of adding fibers to polyelectrolyte hydrogel embolics

[0269] As has been explained in other examples, on a molecular level, the reduction of viscosity during catheter delivery for polyelectrolyte PE hydrogels is due to alignment of the polymer chains in the anionic polysaccharide and dissociation of the charged components from one another under shear. On a larger scale, this alignment of chains can be achieved through the addition of fibers that can add structure to the gel, thereby increasing the elastic modulus, and will align during catheter delivery and increase the rate of viscosity reduction under shear. This concept was demonstrated using fibers made of crosslinked gelatin foam that had been milled and sieved to create branched fibers (FIG 8). The addition of 1 % fibers by weight increased the viscosity at low shear and reduced the injection force through a 0.0235” diameter catheter of length 130 cm at a rate of 1 ml_ per minute (FIG 7A, 7B). Increasing the concentration to 2% further reduced the average injection force but did not continue to increase the viscosity (FIG 7A) or elastic modulus G’ (FIG 7C). This shows there is a balance between the fiber concentration and the polyelectrolyte concentration. For 7% weight PE solids investigated in this example, the 1% concentration is considered ideal.

[0270] Both concentrations of fibers exhibited recovery of the PE hydrogel elastic modulus after 100% strain (FIG 7D). The morphology of the fibers can also play a role in the gel's behavior, much like the linear and branched morphology of anionic polysaccharides can affect its behavior. The crosslinked gelatin fibers used in this example would be considered branched fibers which is desirable for maximizing the elastic modulus at low shear and increasing the rate of viscosity reduction at high shear.

[0271] Example 7: Effect of polyelectrolyte hydrogels containing radiopaque contrast agents

[0272] Compositions of 7% weight PE solids with 0.5 molar added sodium chloride comprising protamine sulfate and xanthan were combined with 25% by weight tantalum particles (1-5 pm) and 200 mgl / mL iohexol powder. Injection of these PE hydrogels showed coiling behavior sized according to the inner diameter of the deployment catheter. The tantalum version could form black coiled masses (FIG 9A) and the iohexol version formed a white coilable PE hydrogel (FIG 9B). Characterization of these radiopaque PE hydrogels was performed according to the priorexamples' procedure. The tantalum containing devices showed higher viscosity at low shear but rapidly dropped with increasing shear and had injection force rates comparable to PE hydrogels with no tantalum (FIG 10B). This reduced force is assumed to be due to the disruption of ionic interactions by the inert tantalum particles, lohexol is soluble and increases the viscosity due to the competing interaction of the iohexol molecule with water, lohexol may also hydrogen bond with xanthan gum which can explain the increased elastic modulus at low strain (FIG 10C, 10D). Similar to the fibers example, the tantalum exhibits less recovery after strain than iohexol or PE hydrogels with no added fibers or contrast agents. This is due to the interruption of ionic interactions between the polyelectrolyte constituents by the tantalum particles, lohexol recovers more slowly than a PE hydrogel with no additives but faster than PE hydrogels with tantalum or fibers (FIG 10D).

[0273] The ability of PE hydrogels to occlude various vessel sizes under a range of pressures and flow rates was investigated with an in vitro flow model. At a flow rate of 20ml_ / min, both tantalum and iohexol PE hydrogels could occlude a simulated tapered vessel of inner diameter 0.012” (304 pm) for greater than five minutes at a peak pressure of 157 mmHg (FIG 11). As the vessel diameter increased, the maximum occlusion pressure decreased. The maximum pressure held also decreased with increasing flow rate.

[0274] Tantalum containing polyelectrolyte PE hydrogels comprising protamine sulfate and xanthan gum with 1.0 molar added sodium chloride were assessed in a domestic swine animal model. Angiograms showed that the PE hydrogels were visible during deployment and created occlusions (FIG 12). Delivery of material was performed through microcatheters ranging in size from 0.022”-0.027” inner diameters and lengths 110 cm to 150 cm.

[0275] Example 8: Transient visibility of iodinated contrast containing PE hydrogel

[0276] The release of iohexol from a PE hydrogel comprising 7% weight PE solids of protamine and xanthan at a 1 : 1 charge ratio with 0.75 molar added sodium chloride was characterized using UV-Vis spectroscopy, lohexol has high absorbance between 240-260 nm and a peak at 245 nm was selected for characterization. A volume of 0.15mL iohexol PE hydrogel was injected into a gelatin vessel mold. The gelatin vessel mold simulates the expected diffusion across vessel walls. The vessel mold containing the iohexol PE hydrogel was placed into a 50 mL centrifuge tube containing 35 mL of balanced salt solution (FIG 13A). This ratio of polyelectrolyte hydrogel to BSS was optimal for measuring the iohexol concentration via UV-Vis spectroscopy over time. A Nanodrop One C UV-Vis Spectrometer (Thermo-Scientific) was used for the experiments.Samples of 40 microliters were taken from the BSS measurements were taken every five minutes after introducing the iohexol PE hydrogel to the gelatin vessel in BSS. The percent dissipation was calculated from the absorption intensity and the average results plotted versus time (FIG 13B).

[0277] After five minutes only 10-23% of the iohexol was released from the PE hydrogels in this example and it took over an hour for iohexol to fully release from the gel. This characteristic of the PE hydrogel architecture allows the embolic to be visible for at least 5 minutes after delivery, but gradually fade so that during follow up CT imaging, no artifact is created.

[0278] Iodinated contrast agents are regularly mixed with embolic materials such as PVA particles, gelatin, or other microspheres to add visibility and let the physician have some visual feedback regarding when the particles exit the catheter. The visibility is faint and fleeting and is usually gone within 5 seconds. This creates a risk of off-target embolization.

[0279] Example 9: Hyaluronic Acid - Protamine gels

[0280] Hyaluronic acid is available in a range of molecular weights ranging from the ultra-low molecular weight versions <10 kDa to over 2million kDa. The low molecular weight versions of HA form viscous liquids rather than semi-solid PE hydrogels. The molarity of added sodium chloride necessary to create a homogeneous PE hydrogel with a hyaluronic acid polyanion ranges from 0 up to 1 molar. Higher molecular weight (>500kDa) versions of hyaluronic acid form a very strong PE hydrogel with shear thinning properties and ability to recover after shear (FIG 14A). The ideal concentration, molecular weight, and sodium chloride concentration of hyaluronic acid PE hydrogels will depend on the desired delivery catheter size and vasculature to be occluded.

[0281] Example 10: Polyelectrolyte Hydrogel Coiling and Catheter Shape Memory

[0282] The PE hydrogel embolics described in the previous examples exhibited the ability to retain the shape of the delivery catheter in simulated physiological conditions. This resulted in a number of desirable behaviors. During a simulated in vitro vessel occlusion, as flow slowed downstream and PE hydrogel embolic material continued to be delivered from the catheter, it spontaneously began to coil and fill the entirety of the larger vessel (FIG 15). The implications of this behavior are that catheters can be selected to create a desired gel-coil diameter. It also means that a wide range of vessel sizes can be occluded depending on the catheter size, the flow conditions, vessel tapering, and amount of material delivered. A larger amount of material delivered will form a denser coil mass and occlude larger vessels.

[0283] Another implication of this behavior is that the shape of the catheter tip can be designed to deliver a particular shape or size of material or influence the behavior. For example, an angled catheter tip will increase the cross-sectional area of delivery and direct the material into the vessel wall to initiate the coiling process. Catheter tip designs that bifurcate the lumen will result in splitting the embolic into two coil streams delivered simultaneously. A wide range of custom behaviors are therefore achievable due to the combination of the PE hydrogel properties and catheter design.

[0284] Example 11 : Role of Salts in Chitosan - Xanthan Gum (CS-XG) PE Hydrogels

[0285] At low ionic concentrations, PE hydrogels made from the polycation chitosan or one of its cationic derivatives and the polyanion xanthan gum ionically bond into small particles forming a viscous colloidal liquid (FIG 17a). In this example, potassium chloride is gradually added to a solution of 4.0% chitosan hydrochloride (Glentham Lifesciences) and 4.5% xanthan gum (Sigma- Aldrich) pH adjusted with sodium hydroxide to 5.5. At approximately 0.48M of KCI, the viscous liquid begins to gel. Additional salt is added to obtain to desired level of shielding. Under backlight it becomes more obvious when the hydrogel is sufficiently shielded. Air bubbles may remain making the gel not quite transparent, but there should be no shadows indicating precipitated polyelectrolytes (FIG 17, top row). Following centrifugation and autoclave, a clear to transparent amber polyelectrolyte hydrogel is realized.

[0286] The characteristics of CS-XG PE hydrogels can vary depending on the type and concentration of salt used. In FIG 18A, a CS-XG hydrogel in a dry petri dish with sodium chloride appears opaque (left), while a CS-XG hydrogel with calcium chloride (middle), and xanthan gum alone (right) appear transparent. A key characteristic of PE hydrogels is demonstrated in FIG 18B and FIG 18C. Balanced salt solution is added to the PE hydrogels and after 2 minutes, the xanthan gum only hydrogel (FIG 18C, right) has nearly dissolved away while the two PE hydrogels have become opaque and remain insoluble.

[0287] The optimal salt concentration for CS-XG gels has a lower and upper bound. The lower bound is determined by the minimum ionic concentration required to ionically shield the polyanion and polycation and form a hydrogel. The upper bound is determined by the solubility of chitosan in the presence of a particular salt or salts. At high salt concentrations, chitosan will salt out and become insoluble. In FIG 18A, the left most PE hydrogel is white colored indicating that chitosan has begun to salt out due to the concentration of sodium chloride. However, sufficient charge remains to maintain a cohesive, insoluble gel in BSS rather than dissolve or fragment. Thisindicates that the salting out phenomenon is a continuum, where even at higher salt concentrations where chitosan begins to salt out, a cohesive hydrogel with all the characteristics desirable for embolization can be realized.

[0288] The lower and upper bound salt concentrations vary by salt type. To determine the upper bound range, solutions of 4.0% chitosan HCI containing either 0, 25, 35, 45, or 55 mg / mL of the chloride salts, NaCI, MgCI2, KCI, and CaCI2 were made. The solutions were allowed to fully hydrate for 1 hour and then 0.25ml_ aliquots were pipetted into a polystyrene 96-well plate. FIG 19A shows the results of the solubility assessment at room temperature where the solubility of the backlit samples is easily seen. Next, the solubility was quantified through UV-VIS Absorbance at 600nm, a wavelength in the visible spectrum with low noise for these samples (FIG 19D). The same experiment was repeated after placing the well plate in a freezer at -20C (FIG 19B, 19E). The results from both experiments show that there is a temperature dependence to the solubility of chitosan in salts, that the larger cations Ca2+and K+have a wider solubility window in terms of mass than Na+and Mg2+, and that monovalent metal cations show increased solubility relative to the divalent metal cations. To compare the salts on a total charge molarity basis, the previous two experiments were repeated with a fixed charge molarity (chloride ion molarity) of 0.85M. This experiment supported the previous conclusions, that larger, monovalent cation salts such as KCI have a higher upper bound in terms of both mass and molarity than divalent salts or the salts of the smaller row 3 metal ions. The steric hindrance of the larger cations is more important than the monovalent or divalent nature of the cation with CaCh having a noticeably higher upper bound for chitosan solubility than NaCI or MgCL. FIG 19F also demonstrates the continuum of solubility where the salt out of chitosan takes place gradually and can be quantified through absorbance.

[0289] To investigate the continuum of positive charge loss with increasing salt concentration chitosan HCI samples, zeta potential measurements were taken using an Anton Paar Litesizer machine. Increased salt concentration will naturally lower the zeta potential, however, if chitosan has completely salted out with no residual solubility, this should be reflected by a zeta potential close to OmV. FIG 20A shows that although it appears that solubility has been lost from visual and absorbance measurements, there is a step down in zeta potential with increasing salt concentrations of 0.45M and 0.85M where GO represents pure chitosan HCI with no added salt. FIG 20A also shows that the chemically modified carboxymethyl chitosan has a zeta potential of about -30mV, demonstrating why modified chitosans with negatively charged functional groups are not suitable for this application.

[0290] The lower bound, determined by the transition from viscous liquid to semi-solid PE hydrogel, and the upper bound, determined by partial solubility loss and full solubility loss at which point the PE hydrogel loses the necessary cohesion for use as an embolic or space filler are shown in FIG 21. FIG 21 A presents the data in terms of total charge molarity (chloride molarity) and FIG21 B presents the data in terms of total salt mass. The divalent cations are more efficient at creating hydrogel than the monovalent cations as can be seen from the MgCh and CaCh lower bound starting at both a lower chloride molarity and lower mass. The larger cations have a much wider range than the smaller cations, and overall calcium chloride is the most efficient salt demonstrating the lowest lower bound and a relatively wide solubility range, with potassium chloride displaying the widest functional range and highest upper bound. The results of these experiments will have slight variation depending on the pH, concentration, molecular weight, and type of chitosan and should be performed prior to deciding the exact salt concentration for a given chitosan or chitosan derivative.

[0291] Example 12: Effect of polyelectrolyte concentration on Chitosan-Xanthan PE Hydrogels

[0292] The effect of polyelectrolyte concentration with charge ratios >1 :1 was studied by making PE hydrogels with a fixed CaCL concentration of 0.27M and a high and low xanthan gum concentration of either 50mg / ml_ or 40mg / ml_ as well as a high and low chitosan concentration of 37 mg / mL or 28 mg / mL. Prior to testing, all samples were sterilized by autoclave for 30 minutes at 121 °C using a vented liquids cycle. FIG 22A shows that the peak viscosity is highest for the high-high formulation. At low XG concentrations, the chitosan concentration has a lower impact on viscosity. FIG 22B shows the effect of concentration on the extent of shear thinning. Xanthan concentration has the largest effect on the viscosity at high shear, but chitosan concentration also clearly has an effect. This indicates that to optimize injection force, lowering the chitosan can be beneficial and will have a smaller impact on the peak viscosity (FIG 22A) or the recovered elastic modulus (FIG 22C) than adjusting the xanthan gum concentration. Calculating the ratio of recovered G’ to shear thinned viscosity at 100s-1as shown in FIG 22D quantifies the design tradeoff of the initial strength of the embolic when it exits the delivery conduit versus the force to inject through a delivery conduit such as a catheter. A higher number is desirable from this ratio and can indicate when adjusting the polycation or polyanion begins to give diminishing returns.

[0293] The lower bound concentration of chitosan in CS-XG PE hydrogels was also studied. Formulations containing 40mg / ml_ XG and 0.30M CaCI2at 3 different charge ratios (CR) or 1+:2‘,2+:3; and 1+:T were observed qualitatively over 24 hours. In FIG 23E after 24 hours, the 1 :2 charge ratio sample has swollen noticeably and is breaking apart. The 1:1 CR is clearly opaque and strongly cohesive. Less opacity is seen for the 2:3 and the 1 :2 has begun to dissolve. Compared to xanthan gum or other anionic polysaccharides alone, the 1:2 charge ratio provides prolonged insolubility that eventually decays over 24 hours. Tuning the duration of cohesion and insolubility with the charge ratio helps adapt the polyelectrolyte hydrogel to different embolic applications. Short term embolics, such as those demonstrated with the 1 :2 or 2:3 charge ratio can be beneficial in areas desiring temporary blockage such as musculoskeletal embolization including epicondylitis, geniculate artery embolization and embolization for frozen shoulder. Permanent embolic agents can be made by selecting a charge ratio of 1:1 or higher and is useful for most hemorrhage, prostate, uterine fibroid, and hypervascular tumor embolization applications.

[0294] Example 13: Strengthening of Chitosan-Xanthan PE Hydrogels in Physiological Media

[0295] CS-XG PE hydrogels, with a varied range of polyelectrolyte concentration and salt types, can continue to strengthen in physiological media in a tunable manner. The PE hydrogels, which begin as a semi-solid with an elastic modulus at least twice as high as their viscous modulus, do not undergo any phase change as is the case for current commercial liquid embolic agents that transition from a liquid to a solid through various mechanisms. Rather, as the salt counterions diffuse out, the PE hydrogels will gradually become stronger elastic semi-solids as the electrostatic interactions between chitosan and xanthan gum become stronger. This increases the safety of the PE hydrogels in permanent embolization applications ensuring that they will not continue to shear thin as changes in blood flow patterns due to high blood pressure, vasospasm, or adjunctive procedures occur.

[0296] To demonstrate the strengthening aspect of CS-XG PE hydrogels, four formulations were tested across a range of XG and CS concentrations and with either 0.75M NaCI, 0.66M KCI or 0.27M CaCI2. All had a pH between 5.7 and 5.95. The results are shown in FIG 24. In FIG 24A- B, the PE hydrogels made with the monovalent ions K+and Na+appear to strengthen more than the Ca2+formulations. This can be explained through the divalent nature of Ca2+bridging the negatively charged branches of xanthan gum and therefore diffusing slower or not at all. The Ca2+formulations also appeared to be more ductile and could undergo significant deformation without breaking and this can be seen from the shape of the yield stress curve. The behaviors of themonovalent and divalent salt PE hydrogels are both useful and can be adapted to meet the needs of specific embolization procedures. In FIG 24A-B, the variation in the Na+formulation was higher than for the other two salts. This is likely due to the higher likelihood of chitosan “salt out” in NaCI relative to the chloride salts comprised of the larger ions K+and Ca2+as demonstrated in Example 11. The strengthening aspects of the PE hydrogels can be optimized through adjusting the concentrations of chitosan and xanthan gum as well as the salt selection or through using combinations of salts. One useful possible combination of salts is potassium chloride and calcium chloride which demonstrated the best solubility compatibility with CS. A lower total mass of salt can be used when calcium chloride is combined with potassium chloride and the PE hydrogel will strengthen faster than calcium chloride alone.

[0297] Example 14: Combination of Polycations in PE Hydrogels

[0298] Combining polycations can tune PE hydrogels to specific functions. pGPMA is more soluble than both salmine and chitosan (CS) and when used in combination can improve the shelf-life by reducing the possibility of salt out and increase the positive charge density beyond what can be achieved with CS alone. At higher concentrations, the viscosity of pGPMA is much lower than CS and can be combined with CS to adjust the PE hydrogel to a desired injection force while maintaining a desired charge ratio or total polyelectrolyte content.

[0299] CS-XG hydrogels exhibit greater tensile viscosity and cohesion than PE hydrogels made with only pGPMA and xanthan gum. In many situations this is desirable, however, with excessive cohesion, detachment from the catheter tip in low flow vessels can take additional time. By combining cations, the strengthening and additional cohesion of CS-XG PE hydrogels can be combined with the improved solubility, injection force, and easy detachment from the catheter of pGPMA PE hydrogels to realize a PE hydrogel with an improved user experience. An ideal formulation for this type of PE Hydrogel, maintains a total polyelectrolyte solids content of about 7.5-10% with a 1 :3 ratio of CS to pGPMA. When CS alone is used at a charge ratio of less than 1 : 1 with xanthan gum, the PE hydrogel will not be permanently insoluble (FIG 23). However, when combined with pGPMA, a concentration of chitosan as low as 0.5-1.5% can be combined with a pGPMA concentration of about 1.5-3.5% to form a PE hydrogel with strengthening characteristics and clean detachment from catheter tips during delivery. A formulation of 3.0% pGPMA, 1 % CS, and 4.8% XG with 30% micronized tantalum powder was tested in the 3D printed kidney flow models and the formula readily detached from the tip and was able to occlude vessels 100-300|jm at pressures greater than 150mmHg and vessels as large as 500 pm at pressures <70mmHg. For all experiments the flow rate was set to 160mL / min (FIG 25A).

[0300] Example 15: Gel Coil and Gel Pledget Formation from Hydrogels

[0301] The gel coil and gel pledget application of CS-XG PE hydrogels was demonstrated with a formulation consisting of 4.2% chitosan HCI, 4.5% xanthan gum, 32.5% tantalum and 0.27M CaCI2with pH 5.70 and results are shown in FIGS 26A-C. The versatility of low viscosity pushing medium is demonstrated in FIG 26A where 0.9% saline and Ultravist contrast pushed 0.1 OmL of CS-XG through a microcatheter with inner diameter of 0.020” and length of 150cm without leaving residue in the hub. Repeated flushes of the lumen did not push any additional material through. Pledget 0.1 OmL injections were repeated ten times with no material noted in the catheter hub or flushed from the lumen of the catheter. The force to inject the pledgets is rate dependent and well within comfortable limits. The injection force peaks as the final amount of material is pushed from the hub into the lumen and then tended to taper off. For the faster injection speed of 1mL / min, the proximal end of the pledget thinned noticeably and elongated. However, after exiting the catheter, it still compacted with itself to form a cohesive mass.

[0302] Gel coils and gel pledgets that undergo reduced or no diffusion of salts can also be made through various methods. One method is to perform dialysis on the PE hydrogel until a desired level of salt diffusion has occurred. The PE hydrogel is loaded into an appropriate delivery system and sterilized. A second method is to prepare the PE hydrogels just prior to use by suspending them in the aqueous delivery medium much like gel foam cubes and pledgets are hydrated prior to use. This method was tested in a 3mL syringe where 0.1 OmL PE hydrogel was pushed into a 3mL syringe with 0.9% saline and suspended in the 3mL syringe for one minute. Then the material was pushed into a 65cm 4Fr glidecath and delivered. As before the pledget comes out in a coil shape and then conforms to itself.Gel coils and pledgets can also be delivered with a hydrophobic medium such as an oil, ethiodized oil, silicone or other suitable hydrophobic liquid. This method maintains a cleaner interface at the PE hydrogel proximal interface but does not exchange ions

[0303] Example 16: Delivery System for Gel Coil and Gel Pledgets

[0304] Described herein is a mechanical delivery system for a gel coil / gel pledget. The delivery system contains a precise volume of embolic material in a single, sterile package. The user canconnect the delivery system to a syringe and catheter to deliver this precise volume of gel coil / gel pledget embolic to the desired vessel site.

[0305] The delivery system, shown in FIG 27, is composed of a vessel containing a precise- volume chamber, a female Luer connection, and a male Luer connection. A precise volume of gel coil / gel pledget embolic material (e.g., 0.1 ml_, 0.2 mL, etc.) is introduced into the delivery system and contained within the precise-volume chamber. Appropriate Luer caps are placed on the vessel Luer connections (i.e., male cap on the female connection; female cap on the male connection) to appropriately contain the embolic material within the precise-volume chamber. The filled delivery system is packaged and sterilized. When needed, the user removes the filled delivery system from its package and disconnects the Luer caps. A syringe filled with the appropriate delivery media (e.g., saline, oil, contrast, ethiodized oil, D5W, DMSO, etc.) is attached to the female connector of the delivery system. This assembly is then attached to a properly prepared delivery catheter via the male Luer connector. The gel coil / gel pledget is delivered to the vessel by advancing the syringe plunger, which causes the delivery media in the syringe to advance the precise volume of gel coil / gel pledget embolic material through the delivery catheter to the desired site.

[0306] It should be emphasized that the above-described embodiments of the present disclosure are merely possible examples of implementations set forth for a clear understanding of the principles of the disclosure. Many variations and modifications may be made to the abovedescribed embodiment(s) without departing substantially from the spirit and principles of the disclosure. All such modifications and variations are intended to be included herein within the scope of this disclosure and protected by the following claims.

Claims

CLAIMS1. A polyelectrolyte hydrogel comprising (a) xanthan gum, (b) one or more polycationic polyelectrolytes, and (c) ions comprising monovalent ions, divalent ions, or a combination thereof.

2. The polyelectrolyte hydrogel of claim 1 , wherein the polyelectrolyte hydrogel has an initial elastic modulus greater than the viscous modulus, wherein the initial elastic modulus of the polyelectrolyte hydrogel decreases under shear during delivery through a conduit, and wherein the elastic modulus of the polyelectrolyte hydrogel recovers to a sufficient level in physiological conditions to occlude or fill the desired location.

3. The polyelectrolyte hydrogel of claim 1 , wherein the elastic modulus and viscosity of the polyelectrolyte hydrogel under shear decrease such that the injection force through a catheter is less than 20 Ibf.

4. The polyelectrolyte hydrogel of claim 1, wherein xanthan gum is from about 1.0 weight percent to about 12 weight percent of the hydrogel.

5. The polyelectrolyte hydrogel of claim 1 , wherein xanthan gum has a molecular weight from about 100 kDa to about 10,000 kDa.

6. The polyelectrolyte hydrogel of claim 1 , wherein the polycationic polyelectrolyte has from 10 mol% to 90 mol% ionized side chains above pH 6.3.

7. The polyelectrolyte hydrogel of claim 1 , wherein the polycationic polyelectrolyte comprises only cationic charged groups.

8. The polyelectrolyte hydrogel of claim 1 , wherein the charge ratio between the polycationic polyelectrolytes and xanthan gum at pH of about 4.5 to about 8 is from 6:1 to 1 :6.

9. The polyelectrolyte hydrogel of claim 1 , wherein the initial elastic modulus is greater than or equal to 200 Pa and less than 6,000 Pa.

10. The polyelectrolyte hydrogel of claim 1 , wherein the polycationic polyelectrolyte is from about 0.70 weight percent to about 15 weight percent of the hydrogel.

11. The polyelectrolyte hydrogel of claim 1 , wherein the polycationic polyelectrolyte comprises a pharmaceutically acceptable salt of chitosan.

12. The polyelectrolyte hydrogel of claim 11 , wherein the pharmaceutically acceptable salt of chitosan is the hydrochloride, glutamate, or acetate salt.

13. The polyelectrolyte hydrogel of claim 11, wherein chitosan has an average molecular weight from about 10 kDa to about 130 kDa.

14. The polyelectrolyte hydrogel of claim 11, wherein chitosan has a degree of deacetylation (DDA) greater than 85%.

15. The polyelectrolyte hydrogel of claim 11 , wherein the pharmaceutically acceptable salt of chitosan is from about 0.70 weight percent to about 8 weight percent of the hydrogel.

16. The polyelectrolyte hydrogel of claim 1 , wherein the polycationic polyelectrolyte has from 85 mol% to 100 mol% ionized side chains at a pH of about 4.5 to 6.3.

17. The polyelectrolyte hydrogel of claim 1 , wherein the polycationic polyelectrolyte comprises a protamine.

18. The polyelectrolyte hydrogel of claim 1, wherein the polycationic polyelectrolyte is salmine or clupein.

19. The polyelectrolyte hydrogel of claim 17, wherein the polycationic polyelectrolyte is from about 0.70 weight percent to about 12 weight percent of the hydrogel.

20. The polyelectrolyte hydrogel of claim 1 , wherein the polycationic polyelectrolyte is a natural polymer or a synthetic polymer containing two or more guanidinyl sidechains.

21. The polyelectrolyte hydrogel of claim 1 , wherein the polycationic polyelectrolyte comprises a polyacrylate comprising two or more pendant guanidinyl groups.

22. The polyelectrolyte hydrogel of claim 1 , wherein the polycationic polyelectrolyte comprises a homopolymer comprising pendant guanidinyl groups.

23. The polyelectrolyte hydrogel of claim 1 , wherein the polycationic polyelectrolyte comprises a copolymer comprising two or more pendant guanidinyl groups.

24. The polyelectrolyte hydrogel of claim 1 , wherein the polycationic polyelectrolyte comprises a synthetic polyguanidinyl copolymer comprising an acrylate, methacrylate, acrylamide, or methacrylamide backbone and two or more guanidinyl groups pendant to the backbone.

25. The polyelectrolyte hydrogel of claim 1 , wherein the polycationic polyelectrolyte comprises a synthetic polyguanidinyl copolymer comprising the polymerization product between a monomer selected from the group consisting of an acrylate, a methacrylate, anacrylamide, a methacrylamide, or any combination thereof and a pharmaceutically- acceptable salt of compound of formula Iwherein R1is hydrogen or an alkyl group, X is oxygen or NR5, where R5is hydrogen or an alkyl group, and m is from 1 to 10.

26. The polyelectrolyte hydrogel of claim 25, wherein the polycationic polyelectrolyte comprises a copolymerization product between the compound of formula I and an acrylate, a methacrylate, an acrylamide, or a methacrylamide,27. The polyelectrolyte hydrogel of claim 25, wherein the polycationic polyelectrolyte comprises a copolymerization product between the compound of formula I and methacrylamide, / V-(2-hydroxypropyl)methacrylamide (HPMA), A / -[3-(A / '- dicarboxymethyl)aminopropyl]methacrylamide (DAMA), / V-(3- aminopropyl)methacrylamide, A / -(1 ,3-dihydroxypropan-2-yl) methacrylamide, N- isopropylmethacrylamide, N-hydroxyethylacrylamide (HEMA), or any combination thereof.

28. The polyelectrolyte hydrogel of claim 25, wherein R1is methyl, X is NH, m is 3.

29. The polyelectrolyte hydrogel of claim 25, wherein the mole ratio of the guanidinyl monomer of formula I to the comonomer is from 1 :20 to 20:1.

30. The polyelectrolyte hydrogel of claim 25, wherein the polyguanidinyl copolymer has an average molar mass from 1 kDa to 1,000 kDa.

31. The polyelectrolyte hydrogel of claim 20, wherein the polycationic polyelectrolyte is from about 0.70 weight percent to about 12.0 weight percent of the hydrogel.

32. The polyelectrolyte hydrogel of claim 1 , wherein the ions comprise sodium ions, potassium ions, calcium ions, magnesium ions, or any combination thereof and chloride ions.

33. The polyelectrolyte hydrogel of claim 1 , wherein the total concentration of the ions in the polyelectrolyte hydrogel is from about 0.1 M to about 2.5 M.

34. The polyelectrolyte hydrogel of claim 1 , wherein the ions comprise calcium ions and chloride ions, wherein the total concentration of the ions in the polyelectrolyte hydrogel is from about 0.10 M to about 2.50 M.

35. The polyelectrolyte hydrogel of claim 1 , wherein the ions comprise sodium ions and chloride ions, wherein the total concentration of the ions in the polyelectrolyte hydrogel is from about 0.10 M to about 2.50 M.

36. The polyelectrolyte hydrogel of claim 1, wherein the ions comprise potassium ions and chloride ions, wherein the total concentration of the ions in the polyelectrolyte hydrogel is from about 0.10 M to about 2.50 M.

37. The polyelectrolyte hydrogel of claim 1 , wherein the ions comprise magnesium ions and chloride ions, wherein the total concentration of the ions in the polyelectrolyte hydrogel is from about 0.10 M to about 2.50 M.

38. The polyelectrolyte hydrogel of claim 1, wherein the polyelectrolyte hydrogel further comprises a contrast agent.

39. The polyelectrolyte hydrogel of claim 38, wherein the contrast agent is a radiographic contrast agent.

40. The polyelectrolyte hydrogel of claim 38, wherein the contrast agent is tantalum metal particles, gold particles, or tantalum oxide particles.

41. The polyelectrolyte hydrogel of claim 38, wherein the contrast agent is a transient contrast agent.

42. The polyelectrolyte hydrogel of claim 41 , wherein the transient contrast agent comprises an iodinated organic compound.

43. The polyelectrolyte hydrogel of claim 42, wherein the iodinated organic compound comprises iopamidol, iodixanol, iohexol, iopromide, iobtiridol, iomeprol, iopentol,iopamiron, ioxilan, iotrolan, iotrol and ioversol, iopanoate, diatrizoic acid, iothalamate, ioxaglate, or any combination thereof.

44. The polyelectrolyte hydrogel of claim 42, wherein the iodinated organic compound comprises an iodinated oil.

45. The polyelectrolyte hydrogel of claim 38, wherein the contrast agent is up to 40 weight percent of the polyelectrolyte hydrogel.

46. The polyelectrolyte hydrogel of claim 1 , wherein the polyelectrolyte hydrogel further comprises natural or synthetic fibers, water-insoluble filler particles, a nanoparticle, or a microparticle.

47. The polyelectrolyte hydrogel of claim 46, wherein the fibers comprise crosslinked gelatin foam fibers.

48. The polyelectrolyte hydrogel of claim 46, wherein the fibers comprise Type A crosslinked gelatin foam fibers or Type A crosslinked gelatin foam fibers.

49. The polyelectrolyte hydrogel of claim 47, wherein the fibers are from 0.1 weight percent to 5 weight percent of the polyelectrolyte hydrogel.

50. The polyelectrolyte hydrogel of claim 1, wherein the polyelectrolyte hydrogel further comprises a bioactive agent.

51. The polyelectrolyte hydrogel of claim 50, wherein the bioactive agent comprises an antibiotic, a pain reliever, an immune modulator, a growth factor, an enzyme inhibitor, a hormone, a messenger molecule, a cell signaling molecule, a receptor agonist, an oncolytic virus, a chemotherapy agent, a receptor antagonist, a nucleic acid, a chemically- modified nucleic acid, or any combination thereof.

52. The polyelectrolyte hydrogel of claim 1, wherein the polyelectrolyte hydrogel further comprises a nonionic polysaccharide.

53. The polyelectrolyte hydrogel of claim 52, wherein the nonionic polysaccharide comprises guar gum, locust bean gum, a modified starch, or a combination thereof.

54. The polyelectrolyte hydrogel of claim 1, wherein the polyelectrolyte hydrogel further comprises silicate nanoparticles.

55. A polyelectrolyte hydrogel comprising (a) a pharmaceutically acceptable salt of chitosan, a polyguanidinyl copolymer, a protamine, or any combination thereof (b) a polyanionicpolyelectrolyte, and (c) ions comprising monovalent ions, divalent ions, or a combination thereof.

56. The polyelectrolyte hydrogel of claim 55, wherein the polyelectrolyte hydrogel has an initial elastic modulus greater than the viscous modulus, wherein the initial elastic modulus of the polyelectrolyte hydrogel decreases under shear during delivery through a conduit, and wherein the elastic modulus of the polyelectrolyte hydrogel recovers to a sufficient level in physiological conditions to occlude or fill the desired location.

57. The polyelectrolyte hydrogel of claim 55, wherein the elastic modulus and viscosity of the polyelectrolyte hydrogel under shear decrease such that the injection force through a catheter is less than 20 Ibf.

58. The polyelectrolyte hydrogel of claim 55, wherein the polyanionic polyelectrolyte comprises a polyanionic polysaccharide.

59. The polyelectrolyte hydrogel of claim 58, wherein the polyanionic polysaccharide comprises xanthan gum, hyaluronic acid, gellan gum, alginic acid, carrageenan, or any combination thereof.

60. The polyelectrolyte hydrogel of claim 58, wherein the polyanionic polyelectrolyte comprises a negatively-charged glycosaminoglycan or an acidic protein.

61. The polyelectrolyte hydrogel of claim 60, wherein the negatively-charged glycosaminoglycan comprises chondroitin sulfate, dermatan sulfate, keratin sulfate, or hyaluronic acid.

62. The polyelectrolyte hydrogel of claim 55, wherein the polyanionic polyelectrolyte comprises xanthan gum.

63. The polyelectrolyte hydrogel of claim 62, wherein xanthan gum is from about 1.0 weight percent to about 12 weight percent of the hydrogel.

64. The polyelectrolyte hydrogel of claim 62, wherein xanthan gum has a molecular weight from about 100 kDa to about 10,000 kDa.

65. The polyelectrolyte hydrogel of claim 1 , wherein the elastic modulus and the viscosity of the polyelectrolyte hydrogel continue to increase after delivery into physiological media.

66. The polyelectrolyte hydrogel of claim 65, wherein the elastic modulus of the polyelectrolyte hydrogel after 30 minutes in physiological media is between 600 Pa and 25,000 Pa.

67. The polyelectrolyte hydrogel of claim 65, wherein the elastic modulus of the polyelectrolyte hydrogel remains greater than the viscous modulus.

68. The polyelectrolyte hydrogel of claim 1 , wherein the polyelectrolyte hydrogel is exposed to a liquid with ionic content less than the polyelectrolyte hydrogel to increase the elastic modulus prior to delivery.

69. The polyelectrolyte hydrogel of claim 68, wherein the elastic modulus continues to increase after delivery into physiological media70. The polyelectrolyte hydrogel of claim 68, wherein, the elastic modulus after delivery into physiological media, remains within ±10% of the initial elastic modulus prior to delivery.

71. A method for reducing or inhibiting flow in a vessel in a subject comprising introducing into the vessel the polyelectrolyte hydrogel of any one of claims 1-70.

72. The method of claim 71, wherein the method reduces or inhibits blood flow to a tumor, an aneurysm, an endoleak, a varicose vein, a varicocele, a gonadal vein, an ovarian vein, a pelvic vein, a gastrointestinal artery, a rectal artery, a mesenteric artery, the gastroduodenal artery, hepatic artery, the splenic artery, an iliac artery, the portal vein, a vascular malformation, geniculate artery, uterine fibroids, prostatic artery, hemorrhoids, middle meningeal artery, or a bleeding wound.

73. The method of claim 71, wherein the method reinforces the inner wall of a blood vessel in the subject.

74. The method of claim 71, wherein the method temporarily reduces blood flow.

75. The method of claim 74, wherein the method temporarily reduces blood flow in musculoskeletal regions.

76. A method for filling a void in a subject comprising introducing into the void the polyelectrolyte hydrogel of any one of claims 1-70.

77. The method of claim 76, wherein the void is within a bone, muscle, skin, cartilage, tissue, or organ or the void is a pouch or sac attached to a bone, muscle, skin, cartilage, tissue, or organ in the subject.

78. The method of claim 76, wherein the void is a left atrial appendage.

79. The method of claim 76, wherein the void is in a lymph node.

80. The method of claim 76, wherein the composition is introduced into the void by a catheter or needle.

81. The method of claim 76, wherein the polyelectrolyte hydrogel is first introduced into the subject by a delivery system followed by introducing a low viscosity liquid, a hydrophobic liquid, an aqueous contrast agent, or any combination thereof into the subject by a syringe, wherein the syringe is connected to the delivery system.

82. The method of claim 81, wherein the delivery system comprises a housing having a first end and a second end, an interior chamber within the housing for containing the polyelectrolyte hydrogel, a first Luer connection at the first end of the housing, and a second Luer connection at the second end of the housing; and a needle or catheter attached to the first Luer connection or the second Luer connection, wherein the first and second Luer connection not attached to the needle or catheter can receive the syringe comprising the low viscosity liquid, a hydrophobic liquid, an aqueous contrast agent, or any combination thereof.

83. The method of claim 81 , wherein the low viscosity fluid is saline, a non-ionic iodinated contrast agent, dextrose, or sterile water for injection.

84. The method of claim 81 , wherein the low viscosity fluid also contains lidocaine, nitroglycerin, or verapamil.

85. The method of claim 81 , wherein the hydrophobic liquid comprises ethiodized oil (Lipiodol), a plant-derived oil, or a silicone.

86. The method of claim 81 , wherein the polyelectrolyte hydrogel is used in combination with one or more coils, plugs, liquid embolics, or gelatin foam.

87. A kit comprising a delivery system for delivering the polyelectrolyte hydrogel of any one of claims 1-70; the polyelectrolyte hydrogel; and instructions for administering the polyelectrolyte hydrogel to a subject.

88. A kit comprisinga delivery system comprising the polyelectrolyte hydrogel of any one of claims 1- 70 contained within the delivery system; and instructions for administering the polyelectrolyte hydrogel to a subject89. The kit of claim 87, wherein the kit further comprises a syringe comprising a low viscosity liquid, a hydrophobic liquid, an aqueous contrast agent, or any combination thereof.

90. The kit claim of 87, wherein the kit further comprises a syringe filled with dehydrated or hydrated fibers or gel modifier.

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