Variable size hydrophobically modified polymers

Abstract

In various aspects, the present invention provides compositions of variable length hydrophobically modified polymers. These variable length hydrophobes disposed along a hydrophilic polymer backbone provide advanced properties and allow for precise control of the behavior of the resulting amphiphilic polymer, including in aqueous solution. Such control allows for the amphiphilic polymer to have enhanced functionality, including enhanced hemostatic functionality, relative to standard single length hydrophobe graft designs.

Description

[0001] This application is a divisional application of Chinese Application No. 201880029067.4, filed on April 13, 2018, entitled "Hydrophobically Modified Polymers of Variable Size".

[0002] Priority

[0003] This application claims the benefit of U.S. Provisional Application No. 62 / 484,985, filed April 13, 2017, the contents of which are hereby incorporated by reference in their entirety. BACKGROUND

[0004] A wide variety of hydrophobically modified (hm) polymers have been made for a variety of uses, such as: paints, industrial thickeners, drug delivery matrices, and hemostatic agents. The association between hydrophobic groups in water causes the polymers to self-assemble into 3-dimensional networks. These associations tend to thicken the resulting aqueous solutions produced from these biopolymers.

[0005] However, hydrophobically modified (hm) polymers generally have a length of hydrophobic grafts grafted onto the polymer backbone. The properties of polymers with variable grafting structure, size, and density have not been investigated. SUMMARY

[0006] In various aspects, the present application provides compositions of hydrophobically modified polymers of variable length. These variable length hydrophobes disposed along the hydrophilic polymer backbone provide advanced properties and allow for precise control of the behavior of the resulting amphiphilic polymer, including in aqueous solution. Such control allows for enhanced functionality of the amphiphilic polymer, including enhanced hemostatic functionality, relative to standard single length hydrophobe graft designs.

[0007] In various embodiments, the present application provides hm polymers or compositions thereof, wherein the modified polymer has at least two different sizes of hydrophobic groups attached to the polymer backbone. These variable length hm polymers are a new class of associative polymers that include associative polymers for water treatment, cosmetic and personal care compositions, drug delivery, wound care, hemostasis, industrial paints / coatings, and other uses.

[0008] In some embodiments, the polymer or composition is an amphiphilic modified polymer. In some embodiments, the polymer is based on a polysaccharide backbone, such as chitosan, alginate, cellulose, pectin, gellan gum, xanthan gum, dextran, and hyaluronic acid, among others. In some embodiments, the polymer is a synthetic (i.e., non-natural) polymer, such as polyethylene glycol, polylactic acid, polyglycolic acid, poly(lactic-co-glycolic acid), poly-epsilon-caprolactone, polyurethane, polymethyl methacrylate, and silicone, among others. In some embodiments, the polymer is chitosan.

[0009] The polymer can have from 2 to about 10 different hydrophobic groups, optionally from 2 to about 5 different hydrophobic groups (e.g., 2, 3, or 4 different hydrophobic groups). The hydrophobic groups can be independently selected from linear, branched, or cyclic hydrocarbon groups. For example, the hydrophobic groups can include at least one saturated hydrocarbon, which is optionally an acyl group (e.g., a fatty aldehyde or a fatty anhydride).

[0010] In some embodiments, the polymer has at least one or at least two of:

[0011] (a) a Ci to C5 hydrocarbon group, optionally substituted with a non-hydrocarbon moiety;

[0012] (b) a C6 to C12 hydrocarbon group, optionally substituted with a non-hydrocarbon moiety;

[0013] (c) a C13 to C28 hydrocarbon group, optionally substituted with a non-hydrocarbon moiety;

[0014] (d) a hydrophobic group having a size greater than C28, optionally substituted with a non-hydrocarbon moiety. Non-hydrocarbon moieties include heteroatoms or groups containing heteroatoms such as O, N, S, or halogens.

[0015] The polymer composition can be formulated as a solid, a liquid, a gel, a foam, or a putty. For example, the polymer can be a solid, which can be lyophilized or can be a dehydrated solution or a dehydrated foam. In some embodiments, the polymer is formulated with one or more solvents. The solvent can include water. In some embodiments, the solvent includes an industrial solvent, which can be an organic solvent. In some embodiments, the solvent is a paint or an industrial coating.

[0016] In some embodiments, the modified polymer is present in the composition from 0.1 wt% to about 5 wt%, or in some embodiments, from 0.5% to 2.0% (e.g., about 0.5%, about 1.0%, 1.5%, or about 2%). In some embodiments, the polymer is formulated with at least one synthetic polymer. Exemplary synthetic polymers include polyethylene, polystyrene, polyacrylate, polyamide, polyester, polyurethane, polysulfide, and polycarbonate. In some embodiments, the synthetic polymer is polyvinyl alcohol.

[0017] The modified polymer can provide antibacterial and / or antifungal properties, which are desirable for many types of garments and fabrics, as well as cosmetic and personal care compositions.

[0018] In some embodiments, the composition is a hemostatic device or dressing for controlling bleeding. A well functioning hemostatic material requires a number of material characteristics. For example, such a material should be easy to apply (ideally, flowable to conform to surfaces, cavities, and / or small areas), be able to create a rapid seal upon contact with bleeding tissue, maintain its mechanical integrity in the face of high pressure blood flow, be easy to remove, and if left behind in the body after use, be safely bioabsorbed. The present application provides a framework for creating a specific hydrophobic design that employs a number of different graft lengths and densities of hydrophobic groups to achieve optimized properties in flowability, tissue adhesion, cohesion, biodegradability, and removability.

[0019] In some embodiments, the modified polymer (e.g., chitosan or other polymers disclosed herein) has both C8 acyl and C18 acyl groups covalently attached to the biopolymer backbone, which is both adhesive to tissue due to the C8 groups and cohesive under a flow of exudate due to the C18 groups. The C8 groups are fluid at both room and body temperature, enabling the polymer to more effectively diffuse to the cell surface, while the C18 on adjacent polymer chains strongly agglomerate the polymer molecules together even in the presence of high exudate or blood flow. Thus, these embodiments can balance adhesive and cohesive properties.

[0020] Alternatively, or in addition, incorporation of small hydrophobic groups, such as C1 to C4 acyl chains, enables chitosan to be more predictably degraded by lysozyme activity in the body. This is important for making a material that can be left behind in the body after wound treatment. More specifically, hydrophobic groups below C6 length do not help improve hemostatic efficacy. However, hydrophobic modification in the C1 to C6 range allows the framework to optimize degradation of the material in the body via lysozyme. Particularly in the case of a surgical hemostat, it is desirable for the hemostatic biomaterial to rapidly degrade after achieving hemostasis.

[0021] In some aspects, the present application provides a method of treating a wound, comprising applying to a bleeding wound a polymer or composition having hemostatic properties. In some embodiments, the wound has a high flow of exudate or blood. In some embodiments, the polymer composition has advantages in tissue adhesion as well as material cohesion (so as to create a barrier even in the presence of high blood flow). In some embodiments, the material degrades in the body within two months, within one month, within two weeks, or within one week, or within about 2 days. In some embodiments, the material is mechanically removable from the wound without damaging underlying tissue. In various embodiments, the modified polymer (in the amount used) is soluble in an aqueous environment.

[0022] The hydrophobically modified (hm) biopolymer material for incorporation into an aqueous or organic solution or suspension can be based on a solution of hm biopolymer at about 0.1 wt% to about 5.0 wt% relative to the total weight of the composition, or in some embodiments, from about 0.5% to about 4%, or from about 0.5% to about 3%, or from about 0.5% to about 2% of the total weight of the composition.

[0023] The hydrophobic moieties can be independently selected from saturated hydrocarbons (e.g., alkanes) and unsaturated hydrocarbons (e.g., alkenes, alkynes), which can be linear, branched, or cyclic hydrocarbons. In some embodiments, the hydrophobic moieties include aromatic hydrocarbons. In some embodiments, the hydrophobic moieties are fatty acids conjugated to polymer functional groups including amines or hydroxyl groups. An exemplary conjugation chemistry is a fatty acid anhydride.

[0024] Other aspects and embodiments of the application will be apparent from the following detailed description. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 Variable size hydrophobically modified (hm) chitosan is shown, including from top: native chitosan (zero grade (0 grade) hm-chitosan), chitosan with a graft density of 5 mole percent available amines along the backbone of C8 hydrophobe (first grade (1 grade) hm-chitosan), and second (2 grade), third (3 grade), and fourth (4 grade) hm-chitosan, meaning that two, three, and four types of hydrophobic species of varying size and structure are found along the polymer backbone.

[0026] Figure 2 Variable size hydrophobically modified polymers applied to different size polymer backbones are shown.

[0027] Figure 3 A comparison of the effect of variable length grafted hm-chitosan versus single length grafted hm-chitosan on heparinized bovine blood is shown. (Left) 5 mole percent C6, 5 mole percent C10 variable length hydrophobically modified chitosan (gel). (Right) 10 mole percent C8 single length hydrophobically modified chitosan (flowable). These two polymers have the same hydrophobic density, but the gelation properties are significantly different, highlighting the importance of hydrophobic graft design for hemostatic or wound treatment functionality.

[0028] Figure 4 Blood gelling experiments are shown. Samples of 1.0 mL each of hm-chitosan solution (2 wt%) were mixed with 0.5 mL each of blood fraction and vortexed thoroughly. The modified polymer compositions included 5 mole percent C12, 1 mole percent C18, 1.5 wt%; 5 mole percent C12, 1 mole percent C18, 1.0 wt%; and 5 mole percent C12, 1.0 wt%.

[0029] Figure 5 Results of blood gelling capabilities for various hydrophobic graft designs along the chitosan backbone are presented. All hydrophobic graft designs were attached to a medium molecular weight chitosan (Primex hqg 400). The hm-chitosan solution was prepared by dissolving 1.5 wt% of the polymer in a 0.2 M aqueous acetic acid solution. Several secondary, tertiary, and quaternary graft designs were described by the molar percentage of amines along the chitosan backbone. Gelation was defined as the ability of a mixture of polymer and blood (citric acid bovine blood (Lampire)) at a 2:1 (v / v) ratio to retain its own weight when the vial was inverted.

[0030] Figure 6 Blood gelation experiments were conducted with blood using five different hm-chitosan constructs at different weight percent (0.5 wt%) and ratios. Samples 4 and 5, incorporating C12 and C18 hydrophobic grafts, exhibited the strongest gelation properties.

[0031] Figure 7 Steady-state shear rheological evaluation of hm-chitosan foam is shown. Adding blood (triangular) to hm-chitosan significantly increases the viscosity beyond that of the foam itself (circular). This is also evident for unmodified chitosan. A mixture of saline foam and blood was also used as a control.

[0032] Figure 8 The steady-state shear rheology of hm-chitosan foams (including foams based on low and high molecular weight chitosan) is evaluated.

[0033] Figure 9 The diagram shows the logarithmic plot of the initial degradation rate of egg white lysozyme on hm-chitosan (chitosan backbone with a medium molecular weight (Primex hgq400)). Samples A through G represent different hydrophobic grafting designs along the chitosan backbone. Samples E, F, and G exhibit much faster initial degradation rates due to the high C1 content in their hydrophobic grafting designs. Detailed Implementation

[0034] In various aspects, the present invention provides compositions of hydrophobically modified polymers of variable length for applications such as wound treatment, drug delivery, cosmetics, and textiles. Although grafting densities vary, known hydrophobically modified polymers generally have a single length of hydrophobic graft attached to the polymer backbone. According to embodiments of the invention, the variable length of the hydrophobic graft arranged along the hydrophilic polymer backbone allows for precise control over the behavior of the resulting amphiphilic polymer. Such control, relative to a standard single-length hydrophobic graft design, allows the amphiphilic polymer to possess enhanced functionality. This enhanced functionality can arise from novel three-dimensional structures formed from these polymers.

[0035] In various embodiments, the present application provides a hydrophobically modified polymer or composition thereof, wherein the modified polymer has at least two different sizes of hydrophobic groups attached to the polymer backbone. These variable length hydrophobically modified polymers are a new class of associative polymers. These polymers provide a higher level of control over how the polymers interact with themselves and with other entities in an aqueous or organic environment. This results in a new class of functional systems that can be used in water treatment, cosmetic and personal care compositions, drug delivery, wound care, hemostasis, industrial paints / coatings, and other uses.

[0036] In some embodiments, the polymer or composition is an amphiphilic modified polymer. In some embodiments, the polymer is based on a polysaccharide backbone, such as chitosan, alginate, cellulose, pectin, gellan gum, xanthan gum, dextran, and hyaluronic acid, among others. In some embodiments, the polymer is a synthetic (i.e., non-natural) polymer, such as polyethylene glycol, polylactic acid, polyglycolic acid, poly(lactic-co-glycolic acid), poly(lactic-co-glycolic acid), polymethyl methacrylate, poly-epsilon-caprolactone, polyurethane, silicone, and the like.

[0037] In some embodiments, the polymer is chitosan having a deacetylation level of about 40 to about 90%, or about 50 to about 80%, wherein about 10% to about 50% of the functional groups are occupied by hydrophobic groups. As used herein, the term "mol%" of a hydrophobic group refers to the % of available amines occupied by the hydrophobic group, assuming a deacetylation level (e.g., in the case of chitosan) of 85%. For example, the modified polymer can have about 5 to about 100 moles of hydrophobic groups per mole of polymer. The polymer has a molecular weight of about 40,000 to about 500,000 Daltons.

[0038] The polymer can have 2 to about 10 different hydrophobic groups, optionally 2 to about 5 different hydrophobic groups (e.g., 2, 3, or 4 different hydrophobic groups). The hydrophobic groups can be independently selected from linear, branched, or cyclic hydrocarbon groups. For example, the hydrophobic groups can include at least one saturated hydrocarbon, which is optionally an acyl group. In some embodiments, the hydrophobic groups include at least one unsaturated hydrocarbon, aromatic hydrocarbon, and / or polyaromatic hydrocarbon.

[0039] In various embodiments, the hydrophobic groups each have 1 to about 100 carbon atoms, or 1 to about 50 carbon atoms. In some embodiments, the hydrophobic groups each have 1 to about 28 carbon atoms. In some embodiments, the polymer (e.g., chitosan) has at least one or at least two of:

[0040] (a) C1 to C5 hydrocarbon groups that are optionally substituted with non-hydrocarbon moieties;

[0041] (b) C6 to C12 hydrocarbyl groups, optionally substituted with non-hydrocarbon moieties;

[0042] (c) C13 to C28 hydrocarbyl groups, optionally substituted with non-hydrocarbon moieties;

[0043] (d) hydrophobic groups larger than C28, optionally substituted with non-hydrocarbon moieties. Non-hydrocarbon moieties include heteroatoms or groups containing heteroatoms such as O, N, S, or halogens.

[0044] In some embodiments, the hydrophobic groups comprise C8 hydrocarbyl groups that are present together with at least one of C14, C16, or C18 hydrocarbyl groups in a ratio of 5: 1 to 20: 1, for example 5: 1 to 15: 1, or in some embodiments, about 10: 1 (C8:C14 / C16 / C18).

[0045] In some embodiments, the hydrophobic groups comprise C10 or C12 hydrocarbyl groups that are present together with at least one of C14, C16, or C18 hydrocarbyl groups in a ratio of 2: 1 to 10: 1, for example 2: 1 to 8: 1, or in some embodiments, about 5: 1 (C10 / C12:C14 / C16 / C18).

[0046] In some embodiments, the hydrophobic groups comprise C1 to C4 hydrocarbons and C6 to C12 hydrocarbons. In some embodiments, the hydrophobic groups comprise C6 to C12 hydrocarbons and C16 to C28 hydrocarbons. In some embodiments, the hydrophobic groups comprise C1 to C4 hydrocarbons, C6 to C12 hydrocarbons, and C16 to C28 hydrocarbons.

[0047] In some embodiments, C1 to C4 hydrocarbyl groups (e.g., C1) are present in a ratio of 5: 1 to 25: 1 relative to other larger hydrophobic grafts (e.g., C6 or larger). In some embodiments, C1 to C4 hydrocarbyl groups are present in a ratio of 5: 1 to about 20: 1, or about 5: 1 to about 15: 1, or about 5: 1 to about 10: 1 relative to larger hydrophobic grafts (e.g., C6 or larger). In some embodiments, C1 to C4 hydrocarbyl groups (e.g., C1) are incorporated into the polymer together with C6 to C12 (e.g., C8 or C10 or C12) and C13 to C28 hydrocarbyl groups (e.g., C16 or C18).

[0048] The polymer composition can be formulated as a solid, liquid, gel, foam, or putty. For example, the polymer can be a solid, which can be lyophilized or can be a dehydrated solution or dehydrated foam. Thus, the polymer can form a solid matrix. In some embodiments, the polymer is formulated with one or more solvents. The solvent can comprise water. In some embodiments, the solvent comprises an industrial solvent, which can be an organic solvent. In some embodiments, the solvent is a paint or industrial coating.

[0049] In some embodiments, the modified polymer is present in the composition from 0.1 wt% to about 5 wt%, or in some embodiments, from 0.5% to 2.0% (e.g., about 0.5%, about 1.0%, 1.5%, or about 2%). In some embodiments, the polymer is formulated with at least one synthetic polymer. Exemplary synthetic polymers include polyethylene, polystyrene, polyacrylate, polyamide, polyester, polyurethane, polysulfide, and polycarbonate. In some embodiments, the synthetic polymer is polyvinyl alcohol.

[0050] The modified polymer can provide antibacterial and / or antifungal properties, providing a unique advantage. For example, the composition can be a fiber or fabric as described in PCT / US2017 / 56887, which is hereby incorporated by reference in its entirety. For example, antimicrobial properties are desirable for many types of clothing and fabric. In some embodiments, the composition is a cosmetic, personal care composition, or a drug delivery matrix, as described in WO 2017 / 177027, which is hereby incorporated by reference in its entirety.

[0051] In some embodiments, the composition is a paint, industrial coating, or industrial thickener. In such embodiments, the polymer provides unique physical properties to the composition, which can provide improved functionality.

[0052] In some embodiments, the composition is a hemostatic device or dressing for controlling bleeding. A well-functioning hemostatic material requires a number of material characteristics, including: (1) the material should be easy to apply (ideally, flowable to conform to surfaces, cavities, and / or small areas), (2) be able to create a rapid seal upon contact with bleeding tissue, (3) maintain its mechanical integrity in the face of high pressure blood flow, (4) be easy to remove, and (5) be safely bioabsorbed if left behind in the body after use. Traditionally, these attributes have been assessed by mixing a number of different components (e.g., polymers, nanoparticles, and proteins) together, as it was assumed that a single material could not provide all of the key characteristics. While a single material that provides tunability in each of these categories is ideal, such a material is difficult to design, as often a chemical that creates a favorable attribute in one aspect (e.g., adhesion) causes an attribute in another aspect (e.g., cohesion) to be out of tune. Here, we describe a framework that, for example, utilizes the available chemistry along the chitosan backbone to create a specific hydrophobic design via free amine groups that employs a number of different grafting lengths and densities of hydrophobic groups to achieve optimized properties in flowability, tissue adhesion, cohesion, biodegradability, and removability.

[0053] In some embodiments, the modified polymer (e.g., chitosan or other polymers disclosed herein) has C8 acyl and C18 acyl groups covalently attached to the biopolymer backbone, which is both adhesive to tissue due to the C8 groups and cohesive under a flow of exudate due to the C18 groups. The C8 groups are fluid at both room and body temperature, enabling the polymer to more effectively spread onto the cell surface, while the C18 groups on adjacent polymer chains strongly agglomerate the polymer molecules together even in the presence of a high flow of exudate or blood. Thus, these embodiments can balance the adhesive and cohesive properties. Traditional chitosan dressings fail due to a lack of adhesion to the wound site or a lack of cohesion once an initial seal is achieved. More specifically, native chitosan is particularly good at adhering to wet, bleeding tissue. However, chitosan's ability to agglomerate together under a high pressure flow of blood is generally limited.

[0054] According to embodiments of the application, certain hydrophobes are advantageous for optimizing adhesion (e.g., to tissue or wound site), while other hydrophobes are more advantageous for improving cohesiveness (e.g., of the artificial clot). As used herein, the term "artificial clot" refers to the physical network of hydrophobically modified polymers, blood cells, and surrounding tissue cells that effectively acts as a solid barrier to prevent further blood loss. In the C6-C12 length range, hydrophobic grafts can be used to improve the adhesion of the dressing. In the C13-C22 length range, hydrophobic grafts can be used to improve the cohesiveness of the dressing. By mixing hydrophobic grafts, for example, C12 and C18 attached to the composition have improved characteristics compared to native chitosan, C12 chitosan alone at 5%, or C18 chitosan alone at 1%. In some embodiments, the polymer has 1-20 mole % C12 hydrophobic groups, or 2-10 mole % C12 hydrophobic groups, or about 5 mole % C12 hydrophobic groups. In some embodiments, the polymer has 0.5-5 mole % C18 hydrophobic groups, for example 0.5-2 mole % (e.g., about 1 mole %) C18 hydrophobic groups. These hydrophobic groups can be present, for example, on a medium molecular weight chitosan (MW ~ 250 kDa).

[0055] For example, in some embodiments, the hemostatic agent composition is an injectable gel. The C12 component allows the gel to firmly attach to the mucosal surface, while the C18 component allows the coagulation matrix properties to be exhibited when blood begins to infiltrate the gel.

[0056] In some embodiments, the hemostatic agent composition is a lyophilized sponge. The dressing not only adheres strongly to the bleeding tissue (relative to native chitosan), but also coagulates together in the presence of considerable blood pressure. While 5 mole % of a single length of C12 adheres to wet tissue significantly more than native chitosan, it fails after the application of blood pressure far above 100 mmHg. Particularly during resuscitation after trauma, there can be a significant risk of rebleeding under resuscitation pressure.

[0057] In some embodiments, the hemostatic agent composition is a transparent film. The film not only adheres strongly to the bleeding tissue (relative to native chitosan), but also coagulates together in the presence of considerable blood pressure. While 5 mole % of a single length of C12 adheres to wet tissue significantly more than native chitosan, it fails after the application of blood pressure far above 30 mmHg. The ability to withstand such pressures would be problematic in most clinical bleeding situations.

[0058] In some embodiments, the hemostatic agent composition is a powder. This powder not only adheres strongly to bleeding tissue (relative to native chitosan), but also coheres together in the presence of considerable blood pressure. While 5 mole% of single-length C12 adheres to wet tissue to a significantly greater degree than native chitosan, it fails in the presence of blood pressure far above 100 mmHg. Likewise, during resuscitation after trauma, there can be a significant risk of re-bleeding under resuscitation pressure.

[0059] In some embodiments, the hemostatic agent composition is a foam, including a sprayable foam made by mixing a solution of hm-chitosan with a liquefied gas under pressure in a canister. Upon opening the canister valve to atmospheric pressure, the gas rapidly expels the hm-chitosan from the canister. The C12 component of this formulation allows the foam to expand greatly relative to the initial gel volume, while the C18 component allows the final foam product to have mechanical integrity. The foam described herein can also be an injectable foam, where a dual-barrel syringe system is utilized that is attached to a mixing tip. Upon mixing the materials in one barrel, hm-chitosan dissolved in dilute aqueous acetic acid, with the materials in the other barrel, a neutral or negatively charged polymer dissolved in water containing a low concentration of sodium bicarbonate, the gas is released. Upon mixing with the acetic acid, the bicarbonate releases carbon dioxide gas, which foams and expands the hm-chitosan. These and related embodiments are disclosed in PCT / US2018 / 025742, which is hereby incorporated by reference in its entirety.

[0060] In some embodiments, the hemostatic agent composition is a moldable putty. The hydrophobically modified chitosan in the form of a moldable putty composition is described in US 9,616,088, which is hereby incorporated by reference in its entirety. For example, a 1.0 wt% (in 0.15 M aqueous lactic acid) gel is relatively thick, but can be mixed with polyvinyl alcohol and sodium tetraborate to produce a putty-like mechanical characteristic. The C12 component of this formulation allows the putty to adhere firmly to mucosal surfaces, while the C18 component allows the putty to exhibit cohesive matrix properties as blood begins to infiltrate the putty.

[0061] Alternatively, or in addition, incorporation of small hydrophobic groups, such as C1 to C4 acyl chains, enables chitosan to be more predictably degraded by lysozyme activity in vivo. This is important for making materials that can be left in the body after wound treatment. More specifically, hydrophobic groups below C6 length do not help improve hemostatic efficacy. However, hydrophobic modification in the C1 to C6 range allows the framework to optimize degradation of the material in vivo via lysozyme. Particularly in the case of surgical hemostatic agents, it is desirable for the hemostatic biomaterial to degrade rapidly after achieving hemostasis. For example, 5 mole% C12 and 30 mole% C1 attached to medium molecular weight chitosan (MW ~ 250 kDa) results in a composition with improved biodegradation characteristics relative to native chitosan, 5 mole% C12 chitosan only, or 30 mole% C1 chitosan only. Other variations are described herein, including variations with C6 to C12 (e.g., C8 or C10 or C12) and C13 to C28 (e.g., C16 or C18). In some embodiments, 10 mole% to 80 mole%, e.g., 10 mole% to 60 mole% of C1 to C4 acyl chains are incorporated. In some embodiments, 20 mole% to 60 mole%, or 20 mole% to 50 mole%, or 20 mole% to 40 mole% of C1 to C4 acyl chains are incorporated.

[0062] In some aspects, the present invention provides a method of treating a wound, comprising applying to a bleeding wound a polymer or composition having hemostatic properties. In some embodiments, the wound has a high exudate or blood flow. In some embodiments, the polymer composition has advantages in terms of tissue adhesion and material cohesion (so that a barrier can be created even under high blood flow). In some embodiments, the material degrades in vivo in about two months, in about one month, or in about two weeks, or in about one week, or in about 2 days. In some embodiments, the material can be mechanically removed from the wound without damaging underlying tissue. In various embodiments, the modified polymer (in the amount used) is soluble in an aqueous environment.

[0063] In some embodiments, the composition has antimicrobial properties. While the mechanism of action of chitosan as an antimicrobial agent is not well understood, it is possible that two key mechanisms of action are at play: (1) penetration into the bacterial cell and intercalation into plasmid DNA, thereby preventing replication, and (2) physical immobilization of the cell due to physical binding of the bacteria into a strong cohesive network. Smaller hydrophobes (e.g., C1-C12) can aid in cell membrane and / or cell wall engagement, while larger hydrophobes (e.g., C13-C22) can aid in the physical binding of the bacteria into the immobilized network. Thus, the variable length design framework along the large span of the polymer (e.g., chitosan) backbone length allows for the creation of many unique molecules that can amplify a given mechanism of bacterial death depending on the clinical situation. Certain bacteria are more susceptible to cell wall penetration (typically gram negative); infections by strong bacteria can be limited to treatment with molecules that work through physical antibacterial action alone (e.g., multi-drug resistant bacteria).

[0064] In some embodiments, and as shown in Figure 1 , the polymeric composition is a secondary (2nd), tertiary (3rd), or quaternary (4th) hm polymer, such as hm-chitosan. Further, and as shown in Figure 2 , the 2nd, 3rd, or 4th biopolymer can be based on a low molecular weight polymer (e.g., 50-200 kDa), a medium molecular weight biopolymer (200-400 kDa), or a high molecular weight polymer (400 to 1,500 kDa).

[0065] An exemplary hm polymer material is hm-chitosan. Chitosan is the common name for a linear, random copolymer composed of β-(1-4)-linked D-glucosamine and N-acetyl-D-glucosamine. The molecular structure of chitosan is composed of a linear backbone linked with glycosidic bonds. Chitosan is the major component of the exoskeleton of crustaceans, such as crabs, shrimps, krill, and crayfish. Additionally, chitosan is the second most abundant natural biopolymer next to cellulose. Commercial chitosan samples are typically prepared by chemical de-N-acetylation of chitin under alkaline conditions. Depending on the source of natural chitin (extracted from exoskeletons) and its production process, chitosan can vary in size (average molecular weight Mw) and degree of N-acetylation (%DA). While the poor solubility of chitosan in water and common organic solvents limits its applications, the reactive amino groups in the chitosan backbone enable the conjugation of chitosan with various molecules and the tuning of its performance in textiles.

[0066] The degree of deacetylation of chitin can range from about 40-100%, or in some embodiments, from 60 to 100%, which determines the charge density. The structure of chitosan (deacetylated) is depicted in Formula 1:

[0067] Formula 1

[0068]

[0069] These repeating monomer units include a free amino group that makes the molecule or compound containing chitosan or its derivatives susceptible to reaction. The hydrophobic modification of the chitosan backbone is achieved by the association of an amphiphilic compound with the amino group, such that the hydrophobic tail of the amphiphilic compound is associated with the hydrophilic backbone structure.

[0070] In some embodiments, the polymer is one or more hm polysaccharides, including but not limited to cellulose, chitosan, alginate, pectin, gellan gum, xanthan gum, dextran, and hyaluronic acid, all of which are abundant natural biopolymers. In some embodiments, the hm biopolymer contains cationic groups. Hm-chitosan, for example, is a stable, strong, and durable biopolymer that is capable of maintaining its functionality at room temperature for an extremely long shelf life. The natural sources of these polysaccharides vary; cellulose is found in plants, while chitosan and alginate are found in the exoskeletons or outer membranes of various living organisms. In some embodiments, hm-chitosan is derived from deacetylated chitin, which can be derived from one or more of crabs, shrimps, krill, and crayfish.

[0071] The form of the natural polymers used can vary so as to include standard states, derivatives, and other various formulations. For example, hm-cellulose can be formed from, but is not limited to, hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, hydroxypropyl methyl cellulose, and / or hydroxyethyl methyl cellulose. Hm-chitosan can be prepared from, but is not limited to, the following salts of chitosan: chitosan lactate, chitosan salicylate, chitosan pyrrolidone carboxylate, chitosan itaconate, chitosan nicotinate, chitosan formate, chitosan acetate, chitosan gallic acid, chitosan glutamate, chitosan maleate, chitosan aspartate, chitosan glycolate, and quaternary amine substituted chitosan and salts thereof. Hm-alginate can be prepared from, but is not limited to, sodium alginate, potassium alginate, magnesium alginate, calcium alginate, and / or aluminum alginate. It should be understood that various other forms of any of these natural polysaccharides that provide suitable functional capabilities can be employed without departing from the scope and spirit of the present application.

[0072] In some embodiments, the polymer component is a mixture of polysaccharides. For example, the mixture can have various different subcategories of a single polymer class. Alternatively, the mixture can include two or more different classes of polymers, such as cellulose and chitosan, alginate and chitosan, and alginate and cellulose.

[0073] In various embodiments, the biopolymer is hm-chitosan, which can be prepared from chitosan having a deacetylation level of about 40% to about 90%, such as about 50% to about 80%, such as about 60% to about 75%. In some embodiments, the degree of substitution of the hydrophobic substituents on the biopolymer (e.g., chitosan) is about 1 to about 100 moles of hydrophobic substituents per mole of biopolymer. In some embodiments, the degree of substitution of the hydrophobic substituents on the polysaccharide is about 20 to about 100 moles of substituents per mole of biopolymer, or about 40 to about 100 moles of substituents per mole of biopolymer, or about 40 to about 65 moles of hydrophobic substituents per mole of biopolymer. In some embodiments, the degree of substitution of the hydrophobic substituents on the biopolymer (e.g., chitosan) is about 1 to about 30 moles of hydrophobic substituents per mole of biopolymer. In some embodiments, the molecular weight of the polymer is about 25,000 to about 1,500,000 grams per mole. In various embodiments, the molecular weight of the biopolymer is in the range of about 40,000 to about 500,000 grams per mole, or about 50,000 to about 250,000 grams per mole, or about 50,000 to about 100,000 grams per mole. As used herein, the term "molecular weight" means weight average molecular weight. Methods of determining the average molecular weight of biopolymers include low angle laser light scattering (LLS) and size exclusion chromatography (SEC). In performing low angle LLS, a dilute solution (typically 2% or less) of the polysaccharide is placed in the path of a monochromatic laser. Light scattered from the sample strikes a detector positioned at a low angle relative to the laser source. Fluctuations in the scattered light over time are correlated to the average molecular weight of the polysaccharide in solution. In performing SEC measurements, a dilute solution (typically 2% or less) of the biopolymer is similarly injected into a packed column. The polysaccharide is separated according to the size of the dissolved polymer molecules and compared to a series of standards to arrive at a molecular weight.

[0074] The hydrophobically modified biopolymer material for incorporation into an aqueous or organic solution or suspension can be based on a solution of hm-biopolymer at about 0.1 wt% to about 5.0 wt% relative to the total weight of the composition, or in some embodiments, about 0.5% to about 4%, or about 0.5% to about 3%, of the total weight of the composition, or about 0.5% to about 2% of the total weight of the composition. In some embodiments, the biopolymer is about 1.0 wt% to about 5.0 wt% relative to the total weight of the biopolymer composition, or in some embodiments, about 1.5% to about 5%, or about 2.0% to about 4% of the total weight of the composition. In some embodiments, the hm-biopolymer solution is dried or lyophilized.

[0075] The hydrophobic portion can be independently selected from saturated hydrocarbons (e.g., alkanes) and unsaturated hydrocarbons (e.g., alkenes, alkynes), which can be linear, branched, or cyclic. In some embodiments, the hydrophobic portion comprises an aromatic hydrocarbon. In some embodiments, the hydrophobic portion is selected from hydrocarbons having from 1 to about 100 carbon atoms, or from about 1 to about 60 carbon atoms, or from about 1 to about 28 carbon atoms, or from about 1 to about 18 carbon atoms.

[0076] The hydrophobic substituent can comprise at least one hydrocarbon group having from about 8 to about 18 carbon atoms, which is attached to the backbone of the one biopolymer, and in some embodiments, the C8to C18group is an alkyl group. In some embodiments, the hydrocarbon group comprises an aralkyl group. As used herein, the term "aralkyl" means a group containing both aromatic and aliphatic structures.

[0077] The modified biopolymer comprises a biopolymer backbone (e.g., chitosan) comprising a hydrophilic reactive functional group (e.g., an amino group) that binds with a hydrophilic reactive head group (e.g., a carbonyl functional group) of an amphiphilic compound (e.g., an aldehyde) to form an hm-chitosan or other hm-polymer. The head group further associates with a hydrophobic tail group. In the current embodiments, the hydrophobic tail can be, for example, a hydrocarbon. Thus, the hydrophobic tail associates with the biopolymer backbone, providing a hydrophobic modification to the molecule extending from the backbone, and can interact with the surrounding environment in a variety of ways, for example, through hydrophobic interactions with the material.

[0078] An example of a procedure for modifying a polymer is as follows.

[0079] Alginates can be hydrophobically modified by exchanging the positively charged counterions (e.g., Na+) of the alginates with t-butyl ammonium (TBA) ions using a sulfonated ion exchange resin. The resulting TBA-alginate is dissolved in dimethyl sulfoxide (DMSO), where an alkyl (or aryl) bromide reacts with the carboxylate groups along the alginate backbone. Alginates can also be modified with a fatty amine group (e.g., dodecyl amine), followed by the addition of l-ethyl-3-(3-dimethylaminopropyl) carbodiimide via EDC coupling.

[0080] Cellulose materials can be hydrophobically modified by first treating the cellulose material with a large excess of a highly basic aqueous solution (e.g., 20 wt% aqueous sodium hydroxide solution). The basic cellulose is then removed from the solution and mixed vigorously with an emulsified solution containing a reactant (e.g., oleic acid), which is an alkyl (or aryl) halide (e.g., dodecyl bromide).

[0081] Chitosan can be hydrophobically modified by reacting an alkyl (or aryl) aldehyde with the primary amine groups along the alginate backbone in 50 / 50 (v / v) % 0.2 M aqueous acetic acid and ethanol. After the reaction, the resulting Schiff base or imine group is reduced to a stable secondary amine by the dropwise addition of the reducing agent sodium cyanoborohydride. Alternatively, fatty acid anhydride chemistry can be used as described herein.

[0082] The degree of substitution of the hydrophobic substituents on the polymer is up to 50% of the available functional groups (e.g., amines in the case of chitosan). For example, the hydrophobic substituents can be added to 10% to 50% of the available amines, or 20 to 50% of the available amines, or 30 to 50% of the available amines.

[0083] In some embodiments, the hydrophobic substituent is derived from an amphiphilic compound, meaning it is composed of a hydrophilic head group and a hydrophobic tail group. The head group binds to the polymer and positions the tail group to extend from the main chain of the polymer scaffold. This makes the hydrophobic tail group available for hydrophobic interactions. The tail group is a hydrocarbon of various forms.

[0084] Hydrocarbons that can be used in accordance with the present disclosure can be classified as saturated hydrocarbons, unsaturated hydrocarbons, and aromatic hydrocarbons. According to this basic classification system, there are many derivatives and further types of compounds built from them. For example, many different compounds include more than one aromatic ring and are generally referred to as polyaromatic hydrocarbons (PAHs). In some embodiments, the hydrophobic moiety is aliphatic. For aliphatic compounds, carbon atoms can be linked together in straight chains, branched chains, or rings (in which case they are referred to as alicyclic). They can be linked by single bonds (alkanes), double bonds (alkenes), or triple bonds (alkynes). In addition to hydrogen, other elements can also be bound to the carbon chain, most commonly oxygen, nitrogen, sulfur, and chlorine. Those of ordinary skill in the art will recognize that other molecules can also be bound to the carbon chain, and that such heteroatomic structures are considered to fall within the scope of the present invention.

[0085] The hydrophobic tail group of the amphiphilic compound bound to the polymer main chain of the present invention is capable of being branched on its carbon backbone and / or allowing for the inclusion of side chains on its carbon backbone. It can be appreciated that the strength of the hydrophobic interaction is based on the available amount of “hydrophobes” that can interact with themselves or each other. Thus, the hydrophobic effect can be further promoted by increasing the amount of hydrophobic tail groups that are interacting and / or the hydrophobic nature. For example, a hydrophobic tail group (which can include a hydrocarbon chain in its original form), can have its hydrophobicity (the ability of the hydrophobic bond and the strength of the hydrophobic interaction) increased by having a hydrophobic side chain attached to one of the carbons of its carbon backbone.

[0086] The side chain can be a straight chain, aromatic, aliphatic, cyclic, polycyclic hydrophobic side chain or any other type of hydrophobic side chain contemplated by one of skill in the art. Some contemplated hydrophobic side chains can include the following.

[0087] Table 1: Linear alkanes

[0088]

[0089]

[0090]

[0091]

[0092] II. Cyclic compounds

[0093] a. alicyclic compounds / cycloalkanes / cycloalkenes: organic compounds that are both aliphatic and cyclic, with or without side chain attachment. Typically include one or more all-carbon rings (which can be saturated or unsaturated), but are not aromatic.

[0094] b. arenes / polycyclic arenes / heterocyclic compounds: organic compounds whose ring structure contains atoms such as nitrogen, oxygen, sulfur, chlorine as part of the ring in addition to carbon. Can be simple aromatic rings, non-aromatic rings. Some examples are pyridine (C5H5N), pyrimidine (C4H4N2), and dioxane.

[0095] Table 2: Cyclic compounds

[0096]

[0097]

[0098] Examples

[0099] Materials and Methods

[0100] Hydrophobic modification of chitosan; synthesis of hm-chitosan using dodecanoic anhydride and palmitic anhydride

[0101] A general method for making variable length hm-chitosan from anhydride chemistry is described below. Two grams of chitosan were dissolved in 100 mL of 0.2 M acetic acid by stirring in a beaker covered with aluminum foil for 30 minutes. The solution was filtered using a vacuum filter. As soon as the chitosan solution was poured from the flask into a 600 mL beaker, 100 mL of ethanol was gradually added to the flask and swirled to remove the remaining chitosan on the sides of the flask. The ethanol and remaining chitosan were poured into the beaker with the remaining chitosan and the solution was heated to 60 °C; the pH was adjusted to 6.0 by dropwise addition of 0.5 M NaOH. In a separate beaker, 20 mL of ethanol was added to a mixture of dodecanoic anhydride (0.24 g for 0.5% modification) and palmitic anhydride (0.061 g for 1% modification); this solution was also heated to 60 °C to completely dissolve the fatty acid anhydride before slowly pouring the solution into the chitosan solution. The mixture was stirred under heat for 24 hours, then the hm-chitosan was precipitated from the solution by dropwise addition of 0.2 M sodium hydroxide.

[0102] Rheology of blood and chitosan solutions

[0103] For the experiments of the present disclosure, an AR2000 Advanced Rheometer with cone and plate geometry was used to measure dynamic viscoelastic properties. The cone had a diameter of 40 mm and an angle of 2 degrees. To ensure that all measurements were within the linear viscoelastic region, a first stress amplitude sweep was performed. After drawing human blood into a heparinized test tube, 1 mL of blood was added to the rheometer plate using a pipette. Then 1 mL of chitosan (or hm-chitosan) solution (or foam) was added to the blood on the plate. As soon as the solutions were combined, the parameters of the rheometer were set and the run was started. The cone was lowered into contact with the solution and the test would be subjected to a sinusoidal strain as the oscillation frequency was increased. The elastic and viscous moduli were obtained over a frequency range of 0.01 Hz to 10 Hz. Dynamic rheology experiments were performed using unmodified chitosan and variable length hydrophobically modified chitosan.

[0104] Foam can

[0105] Variable length hm-chitosan was prepared by attaching dodecyl anhydride (5 mole % of available amines) and oleic anhydride (1 mole % of available amines) to the chitosan backbone (using a similar process to the one described above). All hm-chitosan solutions used contained 1.25% of modified chitosan in lactate solution with C-12 tails and either high or low concentrations of C-18 tails. The hm-chitosan solutions, unmodified solution, and normal saline solution were then loaded into spray cans with AB-46 propellant and a mixture of propane and butane gases, after which they were ready for use. The ratio of solution to propellant in the can was approximately 70 / 30, which was used to calculate the ratio of blood and saline to be added during the trial.

[0106] Foam samples were sprayed directly onto the rheometer test plate, reaching a mass of approximately 500 grams. Blood tests were performed using a 1 μg:1 μL solution (70% of the can mass difference) with heparinized bovine whole blood. If blood was to be added (in the absence of a blood test), tests using physiological saline were performed by adding 400 μL of 0.9 wt% NaCl solution to the mixture for every 500 μL of blood added, or 400 μL of physiological saline solution for every 500 μL of blood added. Tests using α-CD used the same ratio as those using physiological saline: 400 μL of 100 μM α-CD in 0.9 wt% NaCl solution for every 500 μL of blood. After adding blood or treatment agent to the foam, the mixture was then stirred using a micropipette tip to ensure uniform distribution of the blood or treatment agent throughout the foam mixture.

[0107] All steady-state and dynamic rheological analyses were performed on a TA Instruments AR2000 rheometer with a cone and plate geometry of 40 mm in diameter and a cone angle of 4°. All tests were conducted at a physiological temperature of 37°C using a test gap of 118 μm. Dynamic strain scanning was used to determine the linear viscoelastic region of the samples in order to delineate the spectral lines for dynamic frequency measurements.

[0108] Biodegradation

[0109] To measure the initial degradation rate of the material, we measured the viscosity of a 1 wt% hm-chitosan solution (0.2 M acetic acid) exposed to egg lysozyme (1 wt%) after 1 hour. Before adding the lysozyme, the pH of the hm-chitosan solution was adjusted to 5.5 by adding NaOH (1.0 M) dropwise while stirring. The zero-shear viscosity at time = 0 was compared with the zero-shear viscosity at time = 1 h using an AR 2000 stress-controlled rheometer. The initial degradation rate is expressed as (initial viscosity - final viscosity) / (final viscosity).

[0110] result

[0111] exist Figure 3 In this process, 0.5 mL of a 1.5 wt% modified hm-chitosan solution was mixed with 0.5 mL of heparinized bovine blood. Figure 3In the left vial shown, a 5 mole% C6, 5 mole% C10 variable length design of hydrophobically modified chitosan was mixed with blood. The resulting mixture was a gel that held its own weight after the vial was inverted. In the right vial, a 1.5 wt% solution of 10 mole% C8 hydrophobically modified chitosan was mixed with heparinized bovine blood. The native chitosan was a medium molecular weight chitosan (hqc 400 from Primex (Iceland)).

[0112] This is a single length graft design in this experiment that has exactly the same hydrophobic density as the variable length compositions described previously. However, the gelation characteristics of these two solutions when mixed with blood are dramatically different. While these two polymers have the same hydrophobic density, they have dramatically different gelation characteristics. This is a basic example of how the variable length design along the chitosan backbone can lead to optimized results in terms of final material handling and performance characteristics. The hydrophobically modified polymers disclosed herein can be used as hemostatic biomaterials for treating bleeding, from small amounts of oozing in surgery to severe lacerations in trauma events.

[0113] Foams were compared (prior to the gelation experiment) with the gelled foams to ensure that the rheological results were due to blood gelation and not the result of the initial characteristics of the foams. As shown in Figure 6, the hm-chitosan foams appeared to have some structure prior to the addition of blood. To demonstrate that the foam structure did not affect the gelation of the blood, the steady shear viscosity of hm-chitosan (with C12 (5 mole%) and C18 (1 mole%) attached) and unmodified chitosan were compared. Figure 7 As shown in Figure 7, while the viscosity of both the modified and unmodified foams (1.25 wt% initial concentration in the tank) were greater than the physiological saline solution, the addition of blood greatly increased the viscosity due to the gelation of the chitosan polymers. Figure 7 As shown in Figure 7, while the viscosity of both the modified and unmodified foams (1.25 wt% initial concentration in the tank) were greater than the physiological saline solution, the addition of blood greatly increased the viscosity due to the gelation of the chitosan polymers.

[0114] Figure 8 The addition of a variable length hydrophobic tail was also shown to improve the ability of chitosan to gel blood. The addition of a hydrophobic tail to the chitosan backbone (with C12 (5 mole%) and C18 (2.5 mole%) attached) significantly increased the viscosity and yield stress of the foam and blood mixture. Without the addition of the tail, the chitosan foam was unable to successfully gel blood, similar to the results of the variable length hm-chitosan solution. The initial concentration of chitosan and hm-chitosan in the tank was 1.25 wt%.

[0115] Other preferred multivariable embodiments of blood gelation are shown in Table 3 below. "%" refers to mole percent as described elsewhere herein. All hydrophobic design grafts are attached to medium molecular weight chitosan (Primex hqg 400). The preferred concentrations of the following variable-length hm-chitosans are 0.1 wt% to 2.5 wt%. Preferred counter acids are acetic acid, hydrochloric acid, L-lactic acid, citric acid, and glutamic acid, each at a concentration of 1 wt% to 2 wt% in water. Due to the free reaction of the fatty acid anhydride mixture, grafts of different sizes are randomly distributed along the main chain.

[0116] Table 3: Exemplary embodiments of blood gelation

[0117]

[0118]

[0119] A hydrophobically modified polymer was constructed to balance tissue adhesion and material cohesiveness. Generally, biopolymer hemostatic dressings (including chitosan-based dressings) must first adhere rapidly and strongly to the bleeding site to form a firm seal. Furthermore, to stop bleeding, the dressing must possess sufficient cohesiveness to prevent collapse under high-pressure blood flow. Typically, chitosan dressings fail due to a lack of adhesion to the wound site or a lack of cohesiveness once an initial seal is achieved. Natural chitosan is particularly adept at adhering to moist, bleeding tissue. However, the ability of natural chitosan to aggregate under high-pressure blood flow is generally limited.

[0120] According to this disclosure, certain hydrophobic materials are found to be more advantageous for optimizing adhesion, while others are more advantageous for improving cohesion. For example, hydrophobic grafts can be used to improve the adhesion of chitosan dressings in the C6-C12 length range, while hydrophobic grafts can be used to improve the cohesion of dressings in the C13-C22 length range. By mixing hydrophobic grafts, for example in a preferred embodiment, mixing 5 mol% C12 and 1.0 mol% C18 hydrophobic grafts attached to medium molecular weight chitosan (MW~250kDa), a composition with improved characteristics compared to any of the following substances: (1) natural chitosan; (2) only 5% C12 chitosan; or (3) only 1.0% C18 chitosan. This composition achieves the following improvements compared to single-length hydrophobically modified chitosan:

[0121] (A) In the form of an injectable gel:A gel was prepared from a 1.0 wt% solution of variable length modified hm-chitosan (5 mole% C12 and 1.0 mole% C18) in 0.15 M lactic acid in water. The gel was thick, but had flowability to dispense through a syringe. The C12 component in the formulation allowed the gel to adhere firmly to the mucosal surface, while the C18 component allowed the cohesive matrix properties to be exhibited as the blood began to infiltrate the gel.

[0122] (B) In the form of a lyophilized sponge: A sponge was prepared by lyophilizing a 1.0 wt% solution of variable length modified hm-chitosan (5 mole% C12 and 1.0 mole% C18) in 0.2 M acetic acid in water at -40°C and 50 microbar (μbar). The appearance and feel of the sponge was similar to that of a natural chitosan lyophilized sponge or a single length hydrophobically modified chitosan sponge. However, when placed in contact with a bleeding wound, the sponge not only adhered strongly to the bleeding tissue (relative to natural chitosan), but also coagulated together in the presence of a considerable blood pressure. Thus, while the single length 5 mole% C12 adhered to wet tissue to a significantly greater extent than natural chitosan, it failed after the application of a blood pressure well above 100 mm Hg. Particularly during resuscitation after trauma, there can be a significant risk of re-bleeding under resuscitation pressure.

[0123] (C) In the form of a transparent film: A transparent film was prepared by drying a 1.0 wt% solution of variable length modified hm-chitosan (5 mole% C12 and 1.0 mole% C18) in 0.2 M acetic acid in water at 60°C and 1 atmosphere. The appearance and feel of the film was similar to that of a natural chitosan film or a single length hydrophobically modified chitosan film. However, when placed in contact with a bleeding wound, the film not only adhered strongly to the bleeding tissue (relative to natural chitosan), but also coagulated together in the presence of a considerable blood pressure. Thus, while the single length 5 mole% C12 adhered to wet tissue to a significantly greater extent than natural chitosan, it failed after the application of a blood pressure well above 30 mm Hg. The ability to withstand such pressures would be problematic in most clinical bleeding situations.

[0124] (D) In the form of a powder:A powder was prepared by grinding a lyophilized sponge prepared from a solution of 1.0 wt% of a modified hm-chitosan of variable length (5 mole% C12 and 1.0 mole% C18) in 0.2 M aqueous acetic acid at -40 °C and 50 μbar. The powder had a similar appearance and feel to natural chitosan powder or single length hydrophobically modified chitosan powder. However, when in contact with a bleeding wound, the powder not only adhered strongly to the bleeding tissue (relative to natural chitosan), but also coagulated together in the presence of a considerable blood pressure. Thus, while the single length 5 mole% C12 powder adhered to wet tissue to a significantly greater extent than natural chitosan, it failed when a blood pressure far in excess of 100 mm Hg was applied. Similarly, there is a significant risk of re-bleeding under resuscitation pressure during resuscitation after trauma.

[0125] (E) In the form of a sprayable foam: A sprayable foam was prepared using a gel prepared from a solution of 1.0 wt% of a modified hm-chitosan of variable length (5 mole% C12 and 1.0 mole% C18) in 0.15 M aqueous acetic acid. The foam was thick, but could be dispensed into an aluminum can. The can was then pressurized with a liquefied gas (e.g., isobutene, isopentane, dimethyl ether) and the can was crimped together with a valve that allowed the can to open to the atmosphere. The C12 component of the formulation allowed the foam to expand greatly relative to the initial gel volume, while the C18 component allowed the final foam product to have mechanical integrity.

[0126] (F) In the form of an injectable foam: A sprayable foam was prepared using a gel prepared from a solution of 1.0 wt% of a modified hm-chitosan of variable length (5 mole% C12 and 1.0 mole% C18) in 0.2 M aqueous acetic acid. The foam was thick, but could be loaded into one side of a dual barrel syringe. A 0.3 M aqueous solution of sodium bicarbonate was loaded into the other side of the syringe. The materials from both sides were mixed by a mixing tip that aspirated output from both barrels simultaneously. Upon mixing, a reaction between the acetic acid and the sodium bicarbonate occurred, producing carbon dioxide gas. The C12 component of the formulation allowed the foam to expand greatly relative to the initial gel volume, while the C18 component allowed the final foam product to have mechanical integrity.

[0127] (G) In the form of a moldable putty: from A gel prepared from a solution of 1.0 wt% of a modified hm-chitosan of variable length (5 mole% C12 and 1.0 mole% C18) in 0.15 M aqueous acetic acid was thick, but could be mixed with polyvinyl alcohol and sodium tetraborate to produce a putty-like mechanical characteristic. The C12 component of the formulation allowed the putty to adhere strongly to a mucosal surface, while the C18 component allowed the putty to exhibit cohesive matrix properties when the blood began to infiltrate the putty.

[0128] According to the present disclosure, hydrophobically modified chitosan with altered biodegradation characteristics are prepared. Hydrophobic groups below C6 length do not help improve the hemostatic effect of chitosan polysaccharides. However, hydrophobic modification in the C1 to C6 range does allow the framework to optimize the degradation of this material via lysozyme in vivo. Particularly in the case of surgical hemostatic agents, it is desirable that the hemostatic biomaterials degrade rapidly after achieving hemostasis.

[0129] By mixing the hydrophobic grafts, for example in a preferred embodiment, mixing 5% C12 and 30% C1 hydrophobic grafts attached to medium molecular weight chitosan (MW ~ 250 kDa), a composition is made with improved biodegradation characteristics relative to: (1) native chitosan; (2) C12 chitosan alone at 5%; or (3) C1 chitosan alone at 30%.

[0130] In other embodiments, chitosan-based materials can be used as antimicrobial agents due to having a bacteriostatic effect. Although the mechanism of action of chitosan as an antimicrobial agent is not well understood, it is possible that two key mechanisms of action are at play: (1) penetration into the bacterial cell and insertion into plasmid DNA, thereby preventing replication, and (2) physical immobilization of cells due to physical binding of bacteria into a robust, cohesive network. Smaller hydrophobes C1-C12 help to engage with the cell membrane and / or cell wall; larger hydrophobes C13-C22 help to physically bind bacteria into an immobilized network. Thus, the variable length design framework along the large span of the chitosan backbone length allows for the creation of many unique molecules that can amplify a given mechanism of bacterial death depending on the clinical situation. Certain bacteria are more prone to penetration of the cell wall (typically gram-negative); infections by robust bacteria can be limited to treatment with molecules that work through physical bacteriostatic effects only (e.g. bacteria that have become resistant to traditional small molecule antibiotic agents through genetic mutation).

Claims

1. A hydrophobically modified polymer composition, wherein the modified polymer has at least two different sizes of hydrophobic groups attached to the polymer backbone, wherein, The modified polymer has at least two of the following: (a) C1 to C5 hydrocarbon groups; (b) C6 to C12 hydrocarbon groups; (c) C13 to C28 hydrocarbon groups; The hydrophobic group comprises C1 to C4 hydrocarbons and hydrocarbons greater than C6; The polymer is chitosan, and the hydrophobic groups are incorporated through fatty acid anhydride chemicals; The polymer described herein has 10% to 50% functional groups occupied by hydrophobic groups; and The C1 to C4 hydrocarbon groups are incorporated at a rate of 20 mol% to 40 mol% relative to the amino group of chitosan.

2. The polymer composition of claim 1, wherein the polymer has a molecular weight of 40,000 to 500,000 Daltons.

3. The polymer composition of claim 1, wherein it has 2 to 5 different hydrophobic groups.

4. The polymer composition of claim 3, wherein the hydrophobic group comprises a C2 hydrocarbon and a C6 or larger hydrocarbon.

5. The polymer composition of claim 1, wherein it is formulated as a solid, liquid, gel, foam or putty.

6. The polymer composition of claim 5, wherein the polymer is formulated with one or more solvents.

7. The polymer composition of claim 6, wherein the modified polymer is present in an amount of 0.1% to 5% by weight.

8. A flowable composition of hydrophobically modified chitosan, wherein the hydrophobically modified chitosan has linear C14 and / or C16 hydrocarbon groups attached to the chitosan backbone. The hydrophobically modified chitosan further comprises C1 to C4 hydrocarbon groups attached to the chitosan backbone. The C1 to C4 hydrocarbon groups are present in an amount of 20 mol% to 40 mol% relative to the amino group of chitosan, and The hydrophobically modified chitosan described therein has a degree of substitution of up to 50% of the amino groups of the chitosan.

9. The flowable composition of claim 8, wherein the composition is a hydrogel.

10. The flowable composition of claim 8, wherein the composition is a foam.

11. The flowable composition of claim 8, wherein the composition is an aqueous solution.

12. The flowable composition of claim 8, wherein the hydrophobically modified chitosan has a straight-chain C16 hydrocarbon group attached to the chitosan backbone.

13. The flowable composition of claim 8, wherein the hydrophobically modified chitosan has linear C14 hydrocarbon groups attached to the chitosan backbone.

14. The flowable composition of claim 8, wherein the hydrophobically modified chitosan further comprises a hydrocarbon group selected from linear C8 to C12 hydrocarbon groups attached to the chitosan backbone.

15. The flowable composition of claim 14, wherein the C8 hydrocarbon group is present in a ratio of 5:1 to 20:1 relative to the C14 and / or C16 hydrocarbon group.

16. The flowable composition of claim 14, wherein the C10 or C12 hydrocarbon groups are present in a ratio of 2:1 to 10:1 relative to the C14 and / or C16 hydrocarbon groups.

17. The flowable composition of claim 8, wherein the hydrophobic group is incorporated by a fatty acid anhydride chemical.

18. The flowable composition of claim 8, wherein the hydrophobically modified chitosan has a degree of substitution of 10% to 50% of the amino groups of the chitosan.

19. The flowable composition of claim 8, wherein the hydrophobically modified chitosan has a degree of substitution of 30% to 50% of the amino groups of the chitosan.

20. The flowable composition of claim 8, wherein the hydrophobically modified chitosan is present in the composition at a concentration of 0.1% to 5% by weight.

21. The flowable composition of claim 8, wherein the hydrophobically modified chitosan is prepared from high molecular weight chitosan having a molecular weight of 400 kDa to 1,500 kDa.

22. The flowable composition of claim 8, wherein the hydrophobically modified chitosan is prepared from chitosan of medium molecular weight having a molecular weight of 200 kDa to 400 kDa.

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