Ionic polymer composition

Abstract

The present disclosure relates to ionic polymer compositions, including semi-interpenetrating and fully interpenetrating polymer networks, methods of making such ionic polymer compositions, articles made from such ionic polymer compositions, and methods of making and packaging such articles.

Description

This application is a divisional application of the invention application with patent application number 201980060511.3, application date July 17, 2019, and invention title "Ionic Polymer Composition".

[0001] Cross - reference to related applications This application is a partial continuation of U.S. Application Serial No. 16 / 246,292, titled "Ionic Polymer Composition", filed on January 11, 2019, and claims the benefit of U.S. Application Serial No. 62 / 699,497, titled "Ionic Polymer Composition", filed on July 17, 2018. The disclosure of each of the foregoing applications is hereby incorporated by reference in its entirety. Field of the disclosure The present disclosure relates to ionic polymer compositions (including semi - interpenetrating and fully interpenetrating polymer networks), methods for preparing such ionic polymer compositions, articles made from such ionic polymer compositions, and methods for preparing and packaging such articles. Background of the disclosure Fully interpenetrating polymer networks (IPNs) and semi - interpenetrating polymer networks ("semi - IPNs") have been produced from a variety of starting materials and have been used in a variety of applications. IPNs and semi - IPNs can combine the beneficial properties of each of the polymers used to prepare them.

[0004] IPNs and semi - IPNs are described, for example, in U.S. Patent Publication No. 2009 / 0008846, U.S. Patent Publication No. 2013 / 0096691, U.S. Patent Publication No. 2017 / 0107370, U.S. Patent Publication No. 2012 / 0045651, U.S. Patent Publication No. 2012 / 0209396, U.S. Patent Publication No. 2017 / 0327624, U.S. Patent Publication No. 2013 / 0131741, and WO 2017 / 027590 for biomedical applications. Summary of the disclosure For the purposes of this application, "carboxylic acid group" can refer to both the non - ionized (protonated) and ionized (carboxylate) forms of these groups. For the purposes of this application, "sulfonic acid group" can refer to both the non - ionized (protonated) and ionized (sulfonate) forms of these groups.

[0006] For the purposes of this application, "interpenetrating polymer network" or "IPN" is a material that comprises two or more polymer networks that are at least partially intertwined at the molecular scale but are not covalently bonded to each other and cannot be separated unless chemical bonds are broken. "Semi-interpenetrating polymer network" or "semi-IPN" is a material that comprises one or more polymer networks and one or more linear or branched polymers, characterized in that at least one network is penetrated at the molecular scale by at least some linear or branched macromolecules. A semi-interpenetrating polymer network differs from an interpenetrating polymer network in that, in principle, the linear or branched polymer component can be separated from the polymer network component without breaking chemical bonds; it is a polymer blend.

[0007] "Polymer" is a substance that comprises macromolecules, which include homopolymers (polymers derived from one monomer) and copolymers (polymers derived from more than one monomer). "Hydrophobic polymer" is a preformed polymer network that has at least one of the following two properties: (1) a surface water contact angle of at least 45°, and (2) exhibits a water absorption rate of 2.5% or less after 24 hours at room temperature according to ASTM test standard D570. "Hydrophilic polymer" is a polymer network that has a surface water contact angle of less than 45° and exhibits a water absorption rate of greater than 2.5% after 24 hours at room temperature according to ASTM test standard D570. "Ionic polymer" is defined as a polymer that comprises macromolecules containing ionic monomers (such as monomers having carboxylic acid groups, sulfonic acid groups, or both), ionizable monomers (such as monomers having protonated carboxyl groups, protonated sulfonic acid groups, or both), or both ionic monomers and ionizable monomers (generally at least 2% by weight of ionic or ionizable monomers (or both) regardless of their nature and location). Unlike thermoplastic polymers, "thermosetting polymer" is a polymer that does not melt when heated. A thermosetting polymer "sets" into a given shape when first made and thereafter does not flow or melt but decomposes when heated and is typically highly crosslinked and / or covalently crosslinked. Unlike thermosetting polymers, "thermoplastic polymer" is a polymer that melts or flows when heated. Thermoplastic polymers are generally not covalently crosslinked. "Phase separation" is defined as the transformation of a single-phase system into a multi-phase system; in particular, the separation of two immiscible blocks of a block copolymer into two phases, and possibly the formation of small intermediate phases in which a small amount of mixing occurs.

[0008] In certain aspects, the present disclosure relates to ionic polymers that comprise a combination of carboxylic acid groups and sulfonic acid groups. In certain of these aspects, the present disclosure relates to ionic polymers that comprise a combination of underived groups and sulfonic acid-derived groups.

[0009] In some aspects, the present disclosure relates to ionomers comprising a combination of underivatized carboxylic acid groups and sulfonic acid-derived groups, including amino-sulfonic acid-derived carboxylic acid groups.

[0010] In some aspects, the sulfonic acid-derived groups are found only on the surface of the ionomer. In some aspects, the sulfonic acid-derived groups can extend from the surface of the ionomer and into the bulk of the ionomer by at least 10 microns, at least 50 microns, at least 100 microns, at least 250 microns, at least 500 microns, at least 1000 microns, at least 2500 microns, or at least 5000 microns, at least 10000 microns or more, such as extending into the bulk of the ionomer a distance within the range of 0 microns - 10 microns - 25 microns - 50 microns - 100 microns - 250 microns - 500 microns - 1000 microns - 2500 microns - 5000 microns - 10000 microns or more.

[0011] In some aspects, at least 1%, at least 5%, at least 10%, at least 15%, at least 20%, at least 25%, at least 50%, at least 75%, at least 80%, at least 85%, at least 90%, at least 95% or all of the thickness of the ionomer has sulfonic acid-derived groups.

[0012] In some aspects, the sulfonic acid-derived groups extend from the surface of the ionomer into the bulk of the ionomer and are present in a detectable amount up to at least 250 microns, at least 500 microns, at least 1000 microns, at least 2500 microns, at least 5000 microns or at least 10000 microns or more from the surface, such as being present in a detectable amount within the range of 250 microns - 500 microns - 1000 microns - 2500 microns - 5000 microns - 10000 microns or more from the surface.

[0013] In some aspects of these aspects, the concentration of the sulfonic acid-derived groups in the ionomer decreases to no less than 50% of the concentration of the sulfonic acid-derived groups at the surface at up to at least 100 microns, at least 250 microns, at least 500 microns, at least 1000 microns, at least 2500 microns, at least 5000 microns, at least 10000 microns or more from the surface.

[0014] In some aspects, at a depth of 100 microns, the concentration of the sulfonic acid-derived groups in the ionomer can be in the range of 0% - 5% - 10% - 25% - 50% - 75% - 90% - 95% - 100% of the surface concentration of the sulfonic acid-derived groups.

[0015] In some aspects, the ionomers as described herein, including any of the above ionomers, can have a thickness in the range of about 2 mm - 3 mm - 4 mm - 5 mm - 7.5 mm - 10 mm or more.

[0016] In some aspects, the present disclosure relates to interpenetrating polymer networks and semi-interpenetrating polymer networks comprising an ionomer as described herein (including any of the above-described ionomers). Such interpenetrating polymer networks and semi-interpenetrating polymer networks can have, for example, a thickness in the range of about 2 mm - 3 mm - 4 mm - 5 mm - 7.5 mm - 10 mm or more.

[0017] In some aspects, the present disclosure relates to methods of forming an ionomer as described herein and interpenetrating and semi-interpenetrating polymer networks comprising an ionomer as described herein.

[0018] In some aspects, the present disclosure relates to implants formed from an ionomer as described herein and interpenetrating and semi-interpenetrating polymer networks comprising an ionomer as described herein, including orthopedic implants.

[0019] In some aspects, the present disclosure relates to packaged products containing implants formed from an ionomer as described herein and interpenetrating and semi-interpenetrating polymer networks comprising an ionomer as described herein, including orthopedic implants.

[0020] In various embodiments, the implant is at least partially immersed in a divalent cation-containing solution comprising water and one or more divalent metal cations. The divalent cation-containing solution can be, for example, a simulated body fluid containing physiological levels of ions found in body fluids such as synovial fluid or serum or cerebrospinal fluid. In certain embodiments, the divalent cation-containing solution can comprise from 0.1 to 5 mM total divalent metal cations. The concentration of total divalent cations in the solution is the combined concentration of all divalent cations in the solution. (For example, if one liter of solution contains 0.5 millimoles of calcium cations, 0.5 millimoles of magnesium cations, and no other divalent cations, then the solution contains 1.0 mM total divalent cations.) In certain embodiments, the divalent cation-containing solution can comprise calcium ions, magnesium ions, or a combination of calcium ions and magnesium ions. For example, the divalent cation-containing solution can comprise from 0.5 to 5.0 mM calcium ions, generally from 0.5 to 2.0 mM calcium ions, more generally from 0.8 to 1.6 mM calcium ions, and in some embodiments from 1.1 to 1.3 mM calcium ions and other possibilities and / or the divalent cation-containing solution can comprise from 0.2 to 1.5 mM magnesium ions, generally from 0.3 to 1.0 mM magnesium ions, and in some embodiments from 0.5 to 0.7 mM magnesium ions and other possibilities. In certain embodiments, the divalent cation-containing solution can further comprise a monovalent metal ion selected from sodium ions, potassium ions, or a combination of sodium and potassium ions, in which case the divalent cation-containing solution can contain from 0 to 300 mM total monovalent metal cations and other possibilities. In various embodiments, the ionomer comprises carboxylic acid groups, sulfonic acid groups, or a combination of carboxylic acid groups and sulfonic acid groups as described elsewhere herein.

[0021] In various embodiments, the implant comprises an interpenetrating or semi-interpenetrating polymer network comprising a first polymer network containing a first polymer and a second polymer network containing an ionomer as described elsewhere herein.

[0022] In various embodiments, the implant can be selected from hip implants, knee implants, shoulder implants, hand implants, toe implants, or anywhere else in the body where cartilage replacement is desired, as described elsewhere herein. In some embodiments, the implant is configured to repair or replace cartilage in a joint in the body (such as the knee joint, condyle, patella, tibial plateau, ankle joint, elbow joint, shoulder joint, finger joint, thumb joint, glenoid fossa, hip joint, intervertebral disc, facet joint, labrum, meniscus, metacarpophalangeal joint, metatarsophalangeal joint, interphalangeal joint, temporomandibular joint, or wrist joint and any part thereof).

[0023] In certain aspects, the present disclosure relates to implants that maintain their size and mechanical properties under divalent conditions, including orthopedic implants such as those described elsewhere herein.

[0024] In some aspects, the present disclosure relates to implants that maintain a water content (i.e., within ±5 wt%, preferably ±2 wt%, more preferably ±1 wt%) across the entire physiological range of divalent ion concentrations found in living organisms, including synovial fluid of living organisms, particularly mammals, and more particularly humans, including orthopedic implants such as those described elsewhere herein.

[0025] In some aspects, the present disclosure relates to implants, including orthopedic implants such as those described elsewhere herein, that exhibit an absolute weight change percent per mM change in the total divalent cation concentration of less than 10%, less than 5%, less than 3%, less than 2%, or even less than 1% (ideally showing no measurable weight change), e.g., within a total divalent cation concentration range of about 0.1 mM - about 5 mM, including a low physiological divalent cation level of 1.4 mM (0.96 mM Ca 2+ , 0.48 mM Mg 2+ ) to a high physiological divalent cation level of 2.2 mM (1.44 mM Ca 2+ , 0.72 mM Mg 2+ ), and showing to have such property.

[0026] In some aspects, the present disclosure relates to implants, including orthopedic implants such as those described elsewhere herein, that maintain a coefficient of friction of less than 0.1, preferably less than 0.075, more preferably less than 0.05 within a total divalent cation concentration range of about 0.1 mM - about 5 mM, including within a physiological total divalent cation concentration range of about 1.4 mM (0.96 mM Ca 2 + , 0.48 mM Mg 2+ ) - about 2.2 mM (1.44 mM Ca 2+ , 0.72 mM Mg 2+ ).

[0027] The present disclosure includes methods for modifying commonly available commercial hydrophobic thermosetting or thermoplastic polymers, such as polyurethanes or acrylonitrile butadiene styrene (ABS), to provide new materials having new properties such as increased strength, lubricity, electrical conductivity, and abrasion resistance. Various hydrophobic thermosetting or thermoplastic polymers are described below. The present disclosure also includes IPN and semi - IPN compositions, as well as articles made from such compositions and methods of using such articles. The IPN and semi - IPN compositions of the present disclosure can achieve one or more of the following properties: high tensile and compressive strength, low coefficient of friction, high water content and swellability, high permeability, biocompatibility, and biostability.

[0028] Applications of the present disclosure include producing hydrophilic, lubricious articles and coatings to reduce the static and dynamic coefficients of friction between two bearing surfaces and to reduce biofilm formation and / or barnacle formation in marine vessels, other watercraft or waterborne objects, or pipes. In addition, applications of the present disclosure include electrochemical applications that require current conduction or ion permeability, such as proton exchange membranes, fuel cells, filtration devices, and ion exchange membranes. Additionally, the present disclosure can be used as a method for manufacturing supports and moving parts for applications such as engines, pistons, or other machines or machine components. The present disclosure can also be used in many biomedical applications, including cartilage replacements, orthopedic joint replacements and surface resurfacing devices or components thereof, intervertebral discs, stents, blood vessels or catheters, condoms, heart valves, vascular grafts, and both short-term and long-term implants in other areas of the body, such as the skin, brain, spine, gastrointestinal system, larynx, and soft tissues generally. Additionally, the present disclosure can be used as a component of various surgical tools and instruments. In various applications, a drug can be incorporated into the materials of the present disclosure for local drug delivery, including drug delivery vehicles in which a therapeutic agent is released from a polymer matrix.

[0029] As previously described, in certain aspects, the present disclosure relates to ionomers comprising a combination of underivatized carboxylic acid groups and sulfonic acid-derived groups, including amino-sulfonic acid-derived carboxylic acid groups, and methods for forming the same.

[0030] Sulfonic acid functional groups can be incorporated into a pre-formed solid article (i.e., present in solid state, including porous and non-porous articles) comprising a precursor polymer containing carboxylic acid groups. In some embodiments, sulfonic acid functional groups can be incorporated into an already formed IPN or semi-IPN (including gradient IPN or semi-IPN) containing carboxylic acid groups. The general principle is to replace the carboxylic acid groups present on polycarboxylic acids such as polyacrylic acid or polymethacrylic acid and other possibilities in the IPN with sulfonic acid-containing functional groups. In some embodiments, methods are provided that include reacting (a) a solid article comprising a precursor polymer containing carboxylic acid groups with (b) a sulfonic acid-containing compound (e.g., by reacting the carboxylic acid groups of the solid article with an amino sulfonic acid compound such that an amide bond is formed between the carboxylic acid groups of the precursor polymer and the amine group of the amino sulfonic acid compound).

[0031] In certain embodiments, a hydrophilic-hydrophobic IPN containing carboxylic acid groups (e.g., carboxylate ion groups) as proposed in US2013 / 0138210 (incorporated herein by reference) can be sulfonated by amidation using an amine containing sulfonic acid (i.e., amino sulfonic acid). An amide (peptide) bond is formed between the carboxylate of the IPN and the amine in the sulfonic acid.

[0032] In some embodiments, the amino sulfonic acid compound is of the formula (H2N) xR(SO3H) y A compound of or a salt thereof, wherein R is an organic moiety, wherein x is a positive integer and wherein y is a positive integer. In certain embodiments, x can range from 1 to 10, generally from 1 to 5 (i.e., x can be 1, 2, 3, 4, or 5), and y can range from 1 to 10, generally from 1 to 5 (i.e., y can be 1, 2, 3, 4, or 5). In some embodiments, the formula (H2N) x R(SO3H) y The compound has a hydrodynamic radius that allows the molecule to diffuse within the IPN. R can be, for example, a hydrocarbon moiety, such as including a linear, branched, or cyclic hydrocarbon moiety, or a hydrocarbon moiety having a combination of two or more of linear, branched, and cyclic hydrocarbon substituents. The hydrocarbon moiety can be, for example, a C1-C12 hydrocarbon or a polymer moiety including a polymer / oligomer containing a heteroatom. In certain embodiments, the hydrocarbon moiety can be selected from an alkane moiety, an alkene moiety, an alkyne moiety, an aromatic moiety, or a hydrocarbon moiety having a combination of two or more of alkane, alkene, alkyne, or aromatic substituents. In certain embodiments, the sulfamic acid can be selected from taurine and taurine derivatives, including 1-substituted, 2-substituted, 1,1-disubstituted, 2,2-disubstituted, and 1,2-disubstituted taurines, such as 1-hydrocarbon-substituted, 2-hydrocarbon-substituted, 1,1-hydrocarbon-disubstituted, 2,2-hydrocarbon-disubstituted, and 1,2-hydrocarbon-disubstituted taurines, wherein the substituted hydrocarbon can be selected from, for example, the aforementioned hydrocarbon moieties. In other embodiments, the sulfamic acid compound is a compound that results in the formation of 2-acrylamido-2-methylpropanesulfonic acid or acrylamidoethanesulfonic acid.

[0033] In various embodiments, the method includes contacting a solid article comprising a precursor polymer having a carboxylic acid group with a compound containing a sulfonic acid such that the compound containing a sulfonic acid (e.g., a sulfamic acid compound) diffuses into the solid article.

[0034] In various embodiments, the method further includes contacting the solid article comprising a precursor polymer having a carboxylic acid group with a coupling reagent such that the coupling reagent diffuses into the solid article, thereby activating the reactive groups (e.g., carboxylic acid groups) within the solid article and facilitating reaction with the compound containing a sulfonic acid (e.g., by promoting the formation of an amide bond between the carboxylic acid group of the precursor polymer within the solid article and the amine group of the sulfamic acid). In these embodiments, the coupling reagent can be diffused into the solid article before the compound containing a sulfonic acid is diffused into the solid article, the coupling reagent can be diffused into the solid article after the compound containing a sulfonic acid is diffused into the solid article, or the coupling reagent and the compound containing a sulfonic acid can be diffused into the solid article simultaneously. Examples of coupling reagents include triazine-based coupling reagents, as well as carbodiimides, phosphorus and ammonium salts, organophosphorus reagents, and fluoroformamidines Coupling reagents. In certain embodiments, the coupling reagent can be a carbodiimide coupling reagent selected from: 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC), 1,3-bis(2,2-dimethyl-1,3-dioxolan-4-ylmethyl)carbodiimide (BDDC), and 1-cyclohexyl-3-[2-morpholinoethyl]carbodiimide. In certain embodiments, the coupling reagent can be a triazine-based coupling agent selected from: derivatives of 2,4,6-trichloro-1,3,5-triazine, including 2,4-dichloro-6-methoxy-1,3,5-triazine (DCMT), 2-chloro-4,6-dimethoxy-1,3,5-triazine (CDMT), its derivatives with N-methylmorpholine (NMM), 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholine Chloride (DMTMM). As discussed in more detail below, the Applicant has found that by using a suitable coupling agent including a triazine-based coupling reagent under suitable conditions, a sulfonic acid-derived group can be incorporated into a solid article comprising a precursor polymer having a carboxylic acid group at a depth ranging from a few micrometers to several hundred micrometers or throughout the entire depth of the material. In various embodiments, the depth of extension of the sulfonic acid-derived group can be increased by repeating the reaction with a compound containing sulfonic acid.

[0035] The precursor polymer having a carboxylic acid group can be, for example, a homopolymer or a copolymer (such as an alternating copolymer, a random copolymer, a gradient copolymer, a block copolymer, etc.). The precursor polymer having a carboxylic acid group can be selected from, for example, polymers comprising one or more monomers selected from acrylic acid, methacrylic acid, crotonic acid, linolenic acid, maleic acid, fumaric acid, etc.

[0036] In various embodiments, the solid article can comprise an interpenetrating or semi-interpenetrating polymer network, the network comprising a first polymer network containing a first polymer and a second polymer network containing a precursor polymer having a carboxylic acid group. The first polymer can be, for example, a hydrophobic polymer. The first polymer can be, for example, a thermoplastic or a thermosetting polymer. In various embodiments described herein, the first polymer can be a hydrophobic thermoplastic or thermosetting polymer. In certain advantageous embodiments, the first polymer can be a hydrophobic thermoplastic polyurethane, such as a hydrophobic thermoplastic polyether-based polyurethane, etc.

[0037] In some embodiments, the present disclosure relates to an IPN or semi-IPN (also referred to herein as a “hybrid anion IPN or semi-IPN” for convenience), which comprises (a) a first polymer network comprising a first polymer and (b) a second polymer network comprising a crosslinked ionomer containing sulfonic acid-derived groups. For example, the first polymer may comprise the first polymer as described elsewhere herein, and the ionomer may comprise a combination of undervivatized carboxylic acid groups and sulfonic acid-derived carboxylic acid groups. As another example, the first polymer may comprise the first polymer as described elsewhere herein, and the ionomer may comprise a combination of undervivatized carboxylic acid groups, sulfonic acid-derived carboxylic acid groups, and uncharged groups. As another example, the first polymer may comprise the first polymer as described elsewhere herein, and the ionomer may comprise a combination of sulfonic acid-derived carboxylic acid groups, optional uncharged groups, and negligible or no undervivatized carboxylic acid groups (e.g., due to the conversion of all or substantially all undervivatized carboxylic acid groups).

[0038] In some embodiments, the first polymer is a hydrophobic thermoset or thermoplastic polymer, and the hybrid anion IPN or semi-IPN exhibits a lower coefficient of friction than the hydrophobic thermoset or thermoplastic polymer. In some embodiments, the hybrid anion IPN or semi-IPN has higher water swellability than the hydrophobic thermoset or thermoplastic polymer, exhibits higher creep resistance, and / or exhibits higher electrical conductivity and permeability. Some embodiments of the composition further include an antioxidant.

[0039] In some embodiments, the hybrid anion IPN or semi-IPN is formed by diffusing a monomer comprising a carboxylic acid group into a first polymer (e.g., a hydrophobic thermoset or thermoplastic polymer) and polymerizing the monomer to form a precursor polymer comprising carboxylic acid groups. Subsequently, a compound containing sulfonic acid is diffused into the IPN or semi-IPN, and a portion of the carboxylic acid groups in the precursor polymer are derivatized as described elsewhere herein, thereby providing an ionomer comprising a combination of undervivatized carboxylic acid groups and sulfonic acid-derived carboxylic acid groups. The compound containing sulfonic acid may be, for example, an aminosulfonic acid of the formula (H2N) x R(SO3H) y as described above.

[0040] In certain embodiments, the hybrid anion IPN or semi-IPN may be between 15-40% w / w of the ionomer, even more particularly between 25-30.

[0041] In certain embodiments, between 10 - 40 mol%, even more particularly between 21 - 31 mol% of the total amount (referred to herein as the "total amount") of undervivatized carboxylic acid groups and sulfonate-derived carboxylic acid groups in the mixed anion IPN or semi-IPN are sulfonate-derived carboxylic acid groups, and between 90 - 60 mol%, even more particularly between 79 - 69 mol% of the total amount are undervivatized carboxylic acid groups.

[0042] In some embodiments, the mixed anion IPN or semi-IPN further comprises water. In certain cases, a hydration gradient can form from a first portion of the composition to a second portion of the composition. The electrolyte can be dissolved in the water.

[0043] In various embodiments, a hydrophobic thermoset or thermoplastic polymer can be physically entangled or chemically crosslinked with an ionomer (i.e., a polymer comprising a combination of undervivatized carboxylic acid groups and sulfonate-derived carboxylic acid groups).

[0044] In some embodiments, the hydrophobic thermoset or thermoplastic polymer has ordered and disordered domains, and the ionomer can be disposed in the disordered domains.

[0045] In various embodiments, the hydrophobic thermoset or thermoplastic polymer can be selected from polymethyl methacrylate, polydimethylsiloxane, acrylonitrile butadiene styrene, polymethyl methacrylate, and polyurethanes, including polyether-based polyurethanes, polycarbonate-based polyurethanes, silicone polyether-based polyurethanes, and silicone polycarbonate-based polyurethanes.

[0046] In various embodiments, the precursor polymer comprising undervivatized carboxylic acid groups and the ionomer comprising a combination of undervivatized carboxylic acid groups and sulfonate-derived carboxylic acid groups can be formed from one or more monomers selected from acrylic acid, methacrylic acid, crotonic acid, linolenic acid, maleic acid, and fumaric acid.

[0047] In various embodiments, an article is provided that is formed from an ionomer comprising a combination of undervivatized carboxylic acid groups and sulfonate-derived carboxylic acid groups (e.g., amino-sulfonate-derived carboxylic acid groups), wherein the concentration of the undervivatized carboxylic acid groups and the concentration of the sulfonate-derived carboxylic acid groups are substantially constant.

[0048] In various embodiments, an article is provided that is formed from an ionomer comprising a combination of underived carboxylic acid groups and sulfonate-derived carboxylic acid groups, wherein the concentration of the underived carboxylic acid groups and / or the concentration of the sulfonate-derived carboxylic acid groups is relatively constant throughout the article. For example, (a) an article can be provided wherein the concentration of the underived carboxylic acid groups varies by at most + / - 10%, at most + / - 5%, at most + / - 2%, at most + / - 1% or even less throughout the article, and / or (b) an article can be provided wherein the concentration of the sulfonate-derived carboxylic acid groups varies by at most + / - 10%, at most + / - 5%, at most + / - 2%, at most + / - 1% or even less throughout the article.

[0049] In various embodiments, an article is provided that is formed from an ionomer comprising a combination of underived carboxylic acid groups and sulfonate-derived carboxylic acid groups, wherein the concentration of the underived carboxylic acid groups and / or the concentration of the sulfonate-derived carboxylic acid groups varies significantly within the article. For example, an article can be provided wherein (a) between two sites (i.e., two locations) within the article (e.g., between one surface of the article and the opposite surface of the article, between the exterior of the article and the interior of the article, etc.), the concentration of the underived carboxylic acid groups within the article varies by at least + / - 10%, at least + / - 25%, at least + / - 50%, + / - 100%, at least + / - 250%, at least + / - 500%, at least + / - 1000% or more and / or (b) between two sites within the article (e.g., between one surface of the article and the opposite surface of the article, between the exterior of the article and the interior of the article, etc.), the concentration of the sulfonate-derived carboxylic acid groups within the article varies by at least + / - 10%, at least + / - 25%, at least + / - 50%, at least + / - 100%, at least + / - 250%, at least + / - 500%, at least + / - 1000% or more.

[0050] In various embodiments, an article is provided that is formed from an ionomer comprising a combination of underivatized carboxylic acid groups and sulfonate-derived carboxylic acid groups, wherein there is a concentration gradient of the underivatized carboxylic acid groups and / or a concentration gradient of the sulfonate-derived carboxylic acid groups. In some of these embodiments, the gradient can approximate the shape of a step function. For example, (a) an article can be provided in which the concentration of the underivatized carboxylic acid groups decreases as the distance from at least one outer surface of the article increases (e.g., decreases by at least 10%, at least 25%, at least 50%, at least 75%, at least 90% up to 100% from at least one outer surface of the article to an internal site within the article (i.e., an internal location, also referred to herein as a site within the body of the article)), (b) an article can be provided in which the concentration of the underivatized carboxylic acid groups increases as the distance from at least one outer surface of the article increases (e.g., increases by at least 10%, at least 20%, at least 50%, at least 100%, at least 200%, at least 500%, at least 1000% or more from at least one outer surface of the article to an internal site within the article), (c) an article can be provided in which the concentration of the sulfonate-derived carboxylic acid groups within the ionomer decreases as the distance from at least one outer surface of the article increases (e.g., decreases by at least 10%, at least 25%, at least 50%, at least 75%, at least 90% up to 100% from at least one outer surface of the article to an internal site within the article), or (d) an article can be provided in which the concentration of the sulfonate-derived carboxylic acid groups within the ionomer increases as the distance from at least one outer surface of the article increases (e.g., increases by at least 10%, at least 20%, at least 50%, at least 100%, at least 200%, at least 500%, at least 1000% or more from at least one outer surface of the article to an internal site within the article).

[0051] The absolute value of the molar ratio of the sulfonate-derived carboxylic acid groups to the underivatized carboxylic acid groups at various sites within the article can vary widely. The molar ratio of the sulfonate-derived carboxylic acid groups to the underivatized carboxylic acid groups at a given site within the article can range from 100,000:1 or greater (including infinity, where 100% of the underivatized carboxylic acid groups are converted to sulfonate-derived carboxylic acid groups) to 1:100 or less. For example, the molar ratio of the sulfonate-derived carboxylic acid groups to the underivatized carboxylic acid groups at a given site within the article can range from 100,000:1 - 50,000:1 - 25,000:1 - 10,000:1 - 5,000:1 - 2,500:1 - 1,000:1 - 500:1 - 250:1 - 100:1 - 50:1 - 25:1 - 10:1 - 5:1 - 2.5:1 - 1:1 - 1:2.5 - 1:5 - 1:10 - 1:25 - 1:50 - 1:100 (i.e., the range is between any two of the foregoing ratios).

[0052] Articles can be provided that are formed from an ionomer comprising a combination of underivatized carboxylic acid groups and sulfonic acid-derived carboxylic acid groups, where the molar ratio of sulfonic acid-derived carboxylic acid groups to undervatized carboxylic acid groups is relatively constant throughout the article, or where the molar ratio of sulfonic acid-derived carboxylic acid groups to undervatized carboxylic acid groups varies significantly within the article.

[0053] In embodiments where an article is provided that is formed from an ionomer comprising a combination of undervatized carboxylic acid groups and sulfonic acid-derived carboxylic acid groups (where the molar ratio of sulfonic acid-derived carboxylic acid groups to undervatized carboxylic acid groups is relatively constant within the article), the molar ratio can vary throughout the article, for example, by up to + / - 10%, up to + / - 5%, up to + / - 2%, up to + / - 1% or less.

[0054] In embodiments where an article is provided that is formed from an ionomer comprising a combination of undervatized carboxylic acid groups and sulfonic acid-derived carboxylic acid groups (where the molar ratio of sulfonic acid-derived carboxylic acid groups to undervatized carboxylic acid groups varies significantly within the article), between two sites within the article (e.g., between one surface of the article and the opposite surface of the article, between the exterior of the article and the interior of the article, etc.), the molar ratio of sulfonic acid-derived carboxylic acid groups to undervatized carboxylic acid groups can vary by at least + / - 10%, at least + / - 25%, at least + / - 50%, at least + / - 100%, at least + / - 250%, at least + / - 500%, at least + / - 1000% or more. In some embodiments, there can be a gradient in the molar ratio of sulfonic acid-derived carboxylic acid groups to undervatized carboxylic acid groups within the article. For example, the molar ratio of sulfonic acid-derived carboxylic acid groups to undervatized carboxylic acid groups can increase between one surface of the article and the opposite surface of the article, or between the outer surface of the article and the interior of the article. As another example, the molar ratio of sulfonic acid-derived carboxylic acid groups to undervatized carboxylic acid groups can decrease between one surface of the article and the opposite surface of the article, or between the outer surface of the article and the interior of the article.

[0055] In this regard, as described above, an ionomer can be formed from an article comprising a precursor polymer containing undervatized carboxylic acid groups by diffusing a coupling reagent into the article and diffusing a sulfonic acid-containing compound into the article, where the coupling reagent can be diffused into the solid article before, after, or simultaneously with the diffusion of the sulfonic acid-containing compound into the article. Thus, the concentration gradients of undervatized carboxylic acid groups and sulfonic acid-derived carboxylic acid groups within the resulting article can be adjusted independently and thus are generally different from each other. For example, in various embodiments, the molar ratio of sulfonic acid-derived carboxylic acid groups to the concentration of undervatized carboxylic acid groups can decrease as the distance from the outer surface of the article to the interior of the article increases.

[0056] A concentration gradient of sulfonic acid-derived carboxylic acid groups and / or underivatized carboxylic acid groups in the article can provide, for example, a hardness and / or hydration gradient within the article.

[0057] Some embodiments include a second hydrophobic thermoset or thermoplastic polymer that can be disposed in a layer separate from the first hydrophobic thermoset or thermoplastic polymer or can be diffused throughout the first hydrophobic thermoset or thermoplastic polymer.

[0058] In some embodiments, during the manufacturing process, a layer of another material is deposited as a coating onto one surface of an article formed from an ionomer comprising a combination of underivatized carboxylic acid groups and sulfonic acid-derived carboxylic acid groups. This material can be added, for example, to the non-hydrated surface of an article containing a gradient ionomer. The material can be in the form of an adhesive or an adhesive precursor and physically, chemically, or physicochemically adheres to the surface of the article formed from the ionomer, such as the non-hydrated surface of an article containing a gradient ionomer. By disposing the material coating on the surface, the strength of a later-applied adhesive is increased. In some embodiments, the strength is increased because the coating material and the adhesive are the same or similar in composition. In other embodiments, the coating is the same material as the surface of the article. In some embodiments, the coating is a material that is at least partially different from the material at the surface of the article. The coating can be a polymer, copolymer, or polymer blend and, in one embodiment, is a copolymer of polymethyl methacrylate and dimethylaminoethyl methacrylate. The coating can be a thin coating applied during the implant manufacturing process and can be applied in a variety of ways, including (but not limited to) spin coating, spraying, vapor deposition, solution casting, painting, and lithography. In other embodiments, the surface of one side of the article is roughened by applying an organic solvent and / or mechanical methods such as (but not limited to) sanding, sandblasting, lithography, and / or embossing. In some embodiments, the coating is applied to the roughened surface. In other embodiments, there is a roughened surface without any additional coating.

[0059] Another aspect of the present disclosure provides a method for producing a water-swellable IPN or semi-IPN from a hydrophobic thermoset or thermoplastic polymer, the method comprising the steps of: contacting a liquid comprising one or more carboxylic acid group-containing monomers (e.g., consisting of pure monomers or monomers in solution) with a hydrophobic thermoset or thermoplastic polymer in solid form; diffusing the one or more carboxylic acid group-containing monomers into the thermoset or thermoplastic polymer; and polymerizing the one or more carboxylic acid group-containing monomers to form an ionomer comprising carboxylic acid groups within the thermoset or thermoplastic polymer, thereby forming a precursor IPN or semi-IPN having carboxylic acid groups.

[0060] Subsequently, a liquid containing one or more aminosulfonic acid compounds is brought into contact with a precursor IPN or semi-IPN having carboxylic acid groups such that the one or more aminosulfonic acid compounds diffuse into the precursor IPN or semi-IPN under conditions that cause the one or more aminosulfonic acid compounds to react with the carboxylic acid groups of the precursor IPN or semi-IPN to form amide bonds, resulting in the formation of a mixed anion IPN or semi-IPN containing undervivatized carboxylic acid groups and aminosulfonic acid-derived carboxylic acid groups. For example, the aminosulfonic acid of the formula aminosulfonic acid is of the formula (H2N) x R(SO3H) y The compound of can react with the carboxylic acid group -COOH within the precursor IPN or semi-IPN to form -CONH(H2N) x-1 R(SO3H) y group. In various embodiments, before, simultaneously with, or after contact with the liquid containing one or more aminosulfonic acid compounds, a liquid containing a coupling reagent is brought into contact with the precursor IPN or semi-IPN such that the coupling reagent reacts with the carboxylic acid groups to activate the carboxylic acid groups to form amide bonds with the one or more aminosulfonic acid compounds.

[0061] Some embodiments include the step of swelling the mixed anion IPN or semi-IPN with water, for example to form a hydration gradient from a first portion of the composition to a second portion of the composition. The method may also include the step of swelling the mixed anion IPN or semi-IPN with an electrolyte solution.

[0062] In some embodiments, the hydrophobic thermosetting or thermoplastic polymer is selected from polyurethane, polymethyl methacrylate, polydimethylsiloxane, acrylonitrile butadiene styrene, and polymethyl methacrylate, polyether-based polyurethane, polycarbonate-based polyurethane, silicone polyether-based polyurethane, and silicone polycarbonate-based polyurethane, etc. The monomer solution containing carboxylic acid groups for forming an ionic polymer containing carboxylic acid groups within the thermosetting or thermoplastic polymer may be selected from acrylic monomers, methacrylic monomers, crotonic acid monomers, linolenic acid monomers, maleic acid monomers, fumaric acid monomers, and other monomers containing carboxylic acid groups.

[0063] Some embodiments include the step of changing the precursor IPN or semi-IPN or the mixed anion IPN or semi-IPN from a first shape to a second shape, for example by heating the precursor IPN or semi-IPN or the mixed anion IPN or semi-IPN.

[0064] Yet another aspect of the present disclosure provides a medical implant (such as an orthopedic implant, etc.) that includes a water-swellable mixed anion IPN or semi-IPN, including a hydrophobic thermoset or thermoplastic polymer and an ionic polymer that includes a combination of underivatized carboxylic acid groups and sulfonate-derived carboxylic acid groups, the implant having a bone contact surface shaped to conform to a bone surface. Some embodiments further include a fluid capsule disposed in an interior region of the implant. Some embodiments have an insertion portion adapted to be inserted into bone and a joint interface portion adapted to be disposed within a joint space, such as bone screws, sutures, or staples that engage the mixed anion IPN or semi-IPN and are adapted to engage bone to attach the mixed anion IPN or semi-IPN to bone and / or a rod that extends from the bone contact surface and is adapted to be inserted into bone. The medical implant may also be incorporated as a support component for another device (such as a metal-based prosthesis).

[0065] The medical implant may also include an adhesive adapted to attach the medical implant to bone, such as on a bone ingrowth surface formed on the bone contact surface. In some embodiments, the ionic polymer that includes a combination of underivatized carboxylic acid groups and sulfonate-derived carboxylic acid groups forms a concentration gradient from a first portion of the implant to a second portion of the implant. Some embodiments have a second hydrophobic thermoset or thermoplastic polymer adjacent to the first hydrophobic thermoset or thermoplastic polymer, and the ionic polymer includes a combination of underivatized carboxylic acid groups and sulfonate-derived carboxylic acid groups that at least interpenetrate the first hydrophobic thermoset or thermoplastic polymer.

[0066] In some embodiments, an implant formed from the ionic polymer as described herein, including an implant containing the water-swellable mixed anion IPN or semi-IPN as described herein, may have properties that mimic the hardness and lubricity of natural cartilage. In some embodiments, an implant formed from the ionic polymer as described herein, including an implant containing the water-swellable mixed anion IPN or semi-IPN as described herein, may be adapted and configured to replace cartilage in a joint. For example, the implant may have a shape selected from a cap, cup, plug, mushroom, cylinder, rod, and patch. The implant may be adapted to repair or replace cartilage in a joint in the body, such as a knee joint (including the medial compartment knee joint, patellofemoral joint, and total knee joint), knee meniscus, condyle, patella, tibial plateau, ankle joint, elbow joint, shoulder joint (including the labral joint), hand joints (including metacarpophalangeal joints, interphalangeal joints, thumb joints, and the base of the thumb joint), glenoid fossa, hip joint (including the acetabular joint), intervertebral disc, zygapophyseal joint (including the facet joint), labrum, meniscus, foot joints (including metatarsophalangeal joints and interphalangeal joints), jaw joint (including the temporomandibular joint), or wrist joint and any portion thereof.

[0067] In some embodiments, at least a portion of the implant described herein may be configured to instantaneously deform during placement of the implant within a joint.

[0068] Yet another aspect of the present disclosure provides a method of repairing an orthopedic joint, the method comprising the step of replacing native cartilage with a water-swellable mixed anion IPN or semi-IPN according to the present disclosure (including engaging the mixed anion IPN or semi-IPN with the bone surfaces defining the joint). The method may further comprise the step of adhering, suturing, stapling, and / or screwing the mixed anion IPN or semi-IPN to the bone surface. The method may further comprise incorporating the material as a support member for another device, such as a metal-based prosthesis. The method may further comprise the step of inserting a stem portion into the bone surface. The orthopedic joint may be selected from the group consisting of shoulder joint (including glenoid joint), hip joint (including acetabular joint), wrist joint, finger joints, hand joints (including metacarpal joints, thumb joints, base of thumb joints), condylar joints, elbow joints, foot joints (including metatarsal joints and toe joints), jaw joints (including temporomandibular joint), medial knee compartment joint, patellofemoral joint, total knee joint, femoral joint, acetabular joint, elbow, facet joints, and vertebral joints (including facet joints).

[0069] Yet another aspect of the present disclosure provides a hull coating comprising a water-swellable mixed anion IPN or semi-IPN of the present disclosure, the coating having a hull contact surface adapted for attachment to a hull. The coating may further comprise an ultraviolet light protectant and / or an antioxidant. Brief Description of the Drawings Figure 1 Schematic illustration of the process for forming an IPN or semi-IPN of one aspect of the present disclosure. From left to right: the thermoplastic material in this aspect of the present disclosure is polyurethane, which is converted to a semi-IPN of polyurethane and polyacrylic acid. The carboxyl moiety is then derivatized to a sulfonic acid moiety.

[0071] Figure 2 Schematic illustration of the sulfonation method of one aspect of the present disclosure. The polyacrylic acid of the semi-IPN is reacted with taurine and (4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methyl-morpholine chloride) under basic conditions to derivatize a polysulfonic acid derivative of polyacrylic acid and taurine.

[0072] Figures 3A - 3E Illustrating sulfonation ( Figure 3A -E) and non-sulfonation ( Figure 3F ) gradient polyetherurethane-polyacrylic acid (PEU-PAA) test articles as a function of total divalent ion concentration within a series of PAA / PEU percentages: ( Figure 3A ) 17.6% PAA / PEU, ( Figure 3B) 22.2% PAA / PEU, ( Figure 3C ) 25.5% PAA / PEU, ( Figure 3D ) 27.6% PAA / PEU, ( Figure 3E ) 40.7% PAA / PEU, ( Figure 3F ) Unsulfonated gradient PEU-PAA test article with 40.7% PAA / PEU. For all test articles made with different amounts of PAA / PEU percentages, a fitted line was obtained to give the percentage weight loss per millimole of total divalent ion concentration, and the slope is shown at the top of each subplot. Error bars represent standard error; n = 5 for each point. NS: p < 0.1.

[0073] Figure 4 Graph of the normalized sulfonate peak intensity as a function of depth (mm) of the Raman microspectroscopy of the sulfonated gradient PEU-PAA of the present disclosure. Upper panel: Representative of the breathing mode of -SO3 (1045 cm -1 ) versus one of the breathing modes of polyurethane (1640 cm -1 ) intensity plot of the ratio. Lower panel: Cumulative distribution of the ratio of the breathing mode of -SO3 (1045 cm -1 ) versus one of the breathing modes of polyurethane (1640 cm -1 ) as a function of the material depth over a 200 um thickness. Disclosure details The present disclosure includes methods for modifying commonly available commercially hydrophobic thermosetting or thermoplastic polymers to endow them with qualities such as lubricity, permeability, electrical conductivity, and abrasion resistance. Such hydrophobic polymers generally do not absorb water and are generally useful because of their mechanical strength, impermeability, and insulating ability. An exemplary list of hydrophobic polymers that can be modified by the methods of the present disclosure includes the following: acrylonitrile butadiene styrene (ABS), polymethyl methacrylate (PMMA), acrylic acid, celluloid, cellulose acetate, ethylene-vinyl acetate (EVA), ethylene-vinyl alcohol (EVAL), Kydex (trademark acrylic / PVC alloy), liquid crystal polymer (LCP), polyoxymethylene (POM or acetal), polyacrylate (acrylic acid), polyacrylonitrile (PAN or acrylonitrile), polyamide (PA or nylon), polyamideimide (PAI), polyaryl ether ketone (PAEK or ketone), polyhydroxyalkanoate (PHA), polyketone (PK), polyester, polyether ether ketone (PEEK), polyetherimide (PEI), polyethersulfone (PES) - see polysulfone, polyethylene chloride (PEC), polyimide (PI), polymethylpentene (PMP), polyphenylene ether (PPO), polyphenylene sulfide (PPS), polyphthalamide (PPA), polystyrene (PS), polysulfone (PSU), polyvinyl acetate (PVA), polyvinyl chloride (PVC), polyvinylidene chloride (PVDC), Spectralon, styrene-acrylonitrile (SAN), polydimethylsiloxane (PDMS), and polyurethane (PU). As will be described herein, a wide variety of polyurethanes with different hard segment, soft segment, and chain extender compositions can be used.

[0075] One aspect of the present disclosure takes advantage of a property of some modifiable thermosetting or thermoplastic hydrophobic polymers: the presence of ordered and disordered (amorphous) domains within the polymer. For example, certain hydrophobic thermosetting or thermoplastic polymers such as polyurethanes are phase-separated, containing a first domain of hard segments and a second domain of soft segments, and the two domains exhibit different solubilities for the interpenetration of monomers. In polyurethanes, the hard segments are primarily disposed within the ordered domains, while the soft segments are primarily disposed within the disordered (amorphous) domains. (Of course, the starting polymer can contain more than two domains without departing from the scope of the present disclosure.) This difference in properties between the two domains of the phase-separated polymer allows the methods of the present disclosure to endow the polymer with new properties that can extend throughout the bulk of the material or throughout only a portion of the material (e.g., in a particular region or in a gradient). For example, a non-lubricating polymer can be made lubricating; an originally non-conductive polymer can be made conductive; and an originally non-permeable polymer can be made permeable. In addition, the method can be repeated to introduce more than one new property into the starting polymer.

[0076] In some embodiments, phase separation in the polymer allows one or more discrete phases within the polymer to be differentially swollen with, for example, a solvent and / or a monomer, which can then be used to impart new properties. According to the present disclosure, lubricity can be introduced into an otherwise non-lubricious material, for example, by adding and polymerizing one or more monomers containing carboxylic acid groups and then reacting with one or more compounds containing sulfonic acid. In one embodiment, a polymeric material having high mechanical strength and a lubricious surface can be made from an otherwise non-lubricious hydrophobic polymer. By converting the otherwise hydrophobic material into a multiphase material having a solid phase and a liquid (water) phase, the present disclosure addresses the need in the art for lubricious high-strength materials for medical, commercial, and industrial applications.

[0077] In some embodiments, a thermoplastic polyurethane-based polymer having a network containing hard and soft segments can be swollen with a monomer and an optional solvent, as well as an initiator and a crosslinker, such that the soft segments are swollen while generally not affecting the hard segment material. This swelling process is not dissolution of the polymer; rather, the hard segments act as physical crosslinks to hold the material together as the soft segments absorb the monomer and the optional solvent. After monomer polymerization and crosslinking and after reaction with a compound containing sulfonic acid, a second network is formed in the presence of the first network, resulting in an IPN or semi-IPN, where the second polymer (i.e., the polymerized and sulfonated monomer) is primarily sequestered within the soft, amorphous domains of the first polymer. Despite some degree of molecular rearrangement and further phase separation, the hard segments largely remain ordered and crystalline, providing structure and strength to the material.

[0078] The new properties provided by the IPN depend on the properties of the polymerized monomers introduced and on the compound containing sulfonic acid introduced subsequently. Examples of such new properties include lubricity, conductivity, hardness, absorbency, permeability, photoreactivity, and thermoreactivity. After optional swelling in a buffered aqueous solution, the second network of the mixed anion IPN or semi-IPN ionizes, and the mixed anion IPN or semi-IPN is water-swollen and lubricious. Thus, hydrophilicity (i.e., water absorbency) can be introduced into an otherwise hydrophobic material. A hydrophobic polymeric material, such as polyurethane or ABS, can be infiltrated with various mixed anion polymers (polymers containing a combination of undervivatized carboxylic acid groups and sulfamic acid-derived carboxylic acid groups) such that it absorbs water.

[0079] In addition to absorbency, various levels of permeability (transport of water, ions, and / or solutes) can be introduced into an otherwise impermeable material. For example, as described above, hydrophobic polymeric materials such as polyurethanes or ABS can be infiltrated with a mixed anion polymer to enable it to absorb water. This hydration of the material bulk enables the transport of solutes and ions. Through the phase continuity of the hydrated phase of the mixed anion IPN or semi-IPN, transport of solutes and ions and permeability to water can be achieved. This can be used in a variety of applications, including drug delivery, separation processes, proton exchange membranes, and catalytic processes. Permeability can also be used to capture, filter, or chelate solutes when a liquid flows through or across the material. Additionally, due to this permeability, the disclosed materials can be given enhanced resistance to creep and fatigue relative to their component hydrophobic polymers, due to their ability to reabsorb fluid after sustained or repeated loading.

[0080] Similarly, any domain can be doped with any number of materials, such as antioxidants, ions, ionomers, contrast agents, particles, metals, pigments, dyes, biomolecules, polymers, proteins, and / or therapeutic agents. Any one of these materials can be incorporated physically or chemically (e.g., covalently bonded into the IPN or semi-IPN or otherwise included as one or more of its components).

[0081] If, for example, acryloxy, methacryloxy, acrylamido, allyl ether, or vinyl functional groups are incorporated at one or both ends of a thermosetting or thermoplastic polymer and then cured by UV or temperature in the presence of an initiator, the hydrophobic thermosetting or thermoplastic polymer can additionally be crosslinked or copolymerized with a polymer containing carboxylic acid groups. For example, polyurethane dimethacrylate or polyurethane bisacrylamide can be used in the first network by curing in the presence of a solvent such as dimethylacetamide and then evaporating the solvent. Adding chemical crosslinks (not just physical crosslinks) to the IPN can add a level of mechanical stability against creep or fatigue caused by continuous, dynamic loading.

[0082] Alternatively, in cases where the thermoplastic polymer is a polyurethane, multi-arm (multifunctional) polyols or isocyanates can be used to create crosslinks in the polyurethane. In this case, a fully interpenetrating polymer network (rather than a semi-interpenetrating polymer network) is created. The result is a composite material with the high strength and toughness of the polyurethane and the lubricious surface and multiphase bulk behavior of the ionomer. Or, other crosslinking methods can be used, including (but not limited to) γ or electron beam irradiation. These features can be used for load-bearing applications such as artificial joint surfaces, or as more biocompatible, thromboresistant long-term implants in other areas of the body, such as the vascular system or skin. Swelling with water also allows for the absorption of solutes such as therapeutic agents or drugs for local delivery to a target area of the body.

[0083] In another embodiment of the present disclosure, a hydrophobic thermosetting or thermoplastic polymer can be linked to a polymer containing carboxylic acid groups. For example, a polyurethane can be linked via vinyl end-groups. Depending on the reaction rate between the end-groups and the monomers being polymerized, different chain configurations can be produced. For example, if the monomers are much more reactive with themselves than the end-groups are with the monomers, the polymer containing carboxylic acid groups will form almost entirely before being added to the chain. On the other hand, if the reactivity of the monomers and the end-groups is similar, a random graft-type copolymerization will occur. Monomers and end-groups can be selected based on their reaction rates by using, for example, the relative reaction rate tables disclosed in The Polymer Handbook. The result of these will be a hybrid copolymer / interpenetrating polymer network.

[0084] Any number or combination of ethylenically unsaturated monomers or macromonomers (i.e., having reactive double bonds / vinyl groups) can be used alone or in combination with various solvents and selectively introduced into one or more phases of the polymer, provided that at least a portion of such monomers contains a carboxylic acid functional group. Other monomers include (but are not limited to) dimethylacrylamide, acrylamide, N-isopropylacrylamide (NIPAAm), methyl acrylate, methyl methacrylate, 2-hydroxyethyl acrylate / methyl methacrylate.

[0085] In one embodiment, a pre-formed thermoplastic polymer can be immersed in acrylic acid (or a solution of acrylic acid (1% - 100%) or other vinyl monomer solution) as well as a cross-linking agent (such as triethylene glycol dimethacrylate or N,N'-methylenebisacrylamide) and a photoinitiator (such as 2-hydroxy-2-methylpropiophenone). The acrylic acid solution can be based on water, a salt buffer, or an organic solvent such as dimethylacetamide, acetone, ethanol, methanol, isopropanol, toluene, dichloromethane, propanol, dimethyl sulfoxide, dimethylformamide, or tetrahydrofuran. The polymer can be swollen by the monomer (e.g., due to solvation of the soft segments in the polymer). The monomer content in the swollen polymer can range from as low as about 1% to as high as about 90%.

[0086] It should be noted that although acrylic acid is used herein as an exemplary monomer to illustrate various aspects of the present disclosure, it should be understood that various monomers having carboxylic acid groups are also contemplated, including especially one or more of the following: acrylic acid, methacrylic acid, crotonic acid, linolenic acid, maleic acid, and fumaric acid. Similarly, it should be noted that although polyacrylic acid is used herein as an exemplary polymer to generally illustrate various aspects of the present disclosure, it should be understood that polymers of various monomers having carboxylic acid groups are also applicable, including especially one or more of the following: acrylic acid, methacrylic acid, crotonic acid, linolenic acid, maleic acid, and fumaric acid.

[0087] The monomer-swollen polymer can then be removed and placed in a mold made of glass, quartz, or a transparent polymer, and then exposed to UV light (or elevated temperature) to initiate polymerization and crosslinking of the monomer. Alternatively, instead of using a mold, the monomer-swollen polymer can be polymerized while being fully or partially exposed to air or an inert atmosphere (such as nitrogen or argon), or in the presence of another liquid such as an oil (e.g., paraffin, mineral, or silicone oil). Depending on the initiator used, exposure to UV light, IR, or visible light, chemistry, charge, or elevated temperature will cause polymerization and crosslinking of monomers containing carboxylic acid groups within the hydrophobic polymer. As an example, monomers (such as acrylic acid) are polymerized to form an ionomer containing carboxylic acid groups within a preformed thermoplastic hydrophobic matrix, thereby forming an interpenetrating polymer network ("IPN"). The solvent can be extracted by heat and convection or by solvent extraction. Solvent extraction involves using a different solvent (such as water) to extract the solvent from the polymer, while heat or convection relies on the evaporation of the solvent.

[0088] Then 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholine chloride can be used as a catalyst to sulfonate the IPN by amidation reaction of the carboxylic acid groups with an aminosulfonic acid compound such as taurine.

[0089] Swelling of the mixed anion IPN or semi-IPN in an aqueous solution (such as phosphate buffered saline) (or other salt solutions, such as the divalent cation solutions described elsewhere herein) at neutral pH will cause ionization of the carboxylic acid and sulfonic acid groups and further swelling with water and salt. The resulting swollen mixed anion IPN or semi-IPN will have a lubricious surface imparted by the hydrophilic charged polymer and high toughness and mechanical strength imparted by the thermoplastic material. In the case of a polyurethane-based mixed anion IPN or semi-IPN, the mixed anion IPN or semi-IPN will have a structure in which the crystalline hard segments in the polyurethane act as physical crosslinks in the first network, while chemical crosslinks are present in the second network.

[0090] The material can also be crosslinked using γ-radiation or electron beam radiation after synthesis. In one example, a polyurethane / polyacrylic acid can be synthesized and then crosslinked by γ-irradiation, for example, at a dose of, for example, 5, 10, 15, 20, or 25 kGy. In this case, the polymerization of polyacrylic acid will be carried out in the absence of a crosslinking agent, and after forming the polymer blend (physical IPN), the material is exposed to γ-radiation. Crosslinking of polyacrylic acid hydrogels using γ-irradiation is known in the art to exhibit a dose-dependence for polymer crosslinking. In the case of polyurethane, the polyurethane polymer can be a commercially available material, a modification of a commercially available material, or a new material.

[0091] Any number of chemicals and stoichiometries can be used to produce polyurethane polymers. For the hard segments, the isocyanates used are 1,5-naphthalene diisocyanate (NDI), isophorone diisocyanate (IPDI), 3,3-dimethylbiphenyl diisocyanate (TODI), methylene bis(p-cyclohexyl isocyanate) (H 12 MDI), cyclohexyl diisocyanate (CHDI), 2,6-toluene diisocyanate (or 2,4-toluene diisocyanate (TDI), hexamethylene diisocyanate or methylene bis(p-phenyl isocyanate)). For the soft segments, the chemicals used include, for example, polyalkylene oxides such as polyethylene oxide (PEO), polypropylene oxide (PPO), polybutylene oxide (PBO), polybutadiene, polydimethylsiloxane (PDMS), polyethylene adipate, polycaprolactone, polytetramethylene glycol adipate, polyisobutylene, polyhexamethylene carbonate diol, poly(1,6-hexyl 1,2-ethyl carbonate). If end groups reactive with isocyanates are used, any number of telechelic polymers can be used in the soft segments. For example, hydroxy- or amine-terminated polyvinylpyrrolidone, dimethylacrylamide, carboxylic acid esters or sulfonated polymers, telechelic hydrocarbon chains (having hydroxy and / or amine end groups), dimethylolpropionic acid (DMPA) or combinations thereof with each other or with the other soft segments mentioned above (such as PDMS) can be used.

[0092] Chain extenders include, for example, 1,4-butanediol, ethylenediamine, 4,4′-methylenebis(2-chloroaniline) (MOCA), ethylene glycol and hexanediol. Any other compatible chain extenders can be used alone or in combination. Crosslinking chain extenders containing isocyanate-reactive end groups (such as hydroxy or amine) can be used, and vinyl-based functional groups (such as vinyl, methacrylate, acrylate, allyl ether or acrylamide) can be used to replace some or all of the chain extenders. Examples include 1,4-dihydroxybutene and glycerol methacrylate. Alternatively, crosslinking can be achieved by using polyols such as glycerol (which contains more than two hydroxy groups to react with isocyanates).

[0093] In some embodiments, at least 1% of the monomers in the second network contain carboxylic acid groups. In one such embodiment, a polyacrylic acid (PAA) hydrogel is used as the second polymer network, which is formed from an aqueous solution of acrylic acid monomers. Other monomers containing carboxylic acid groups include, for example, methacrylic acid. These other monomers can also be in the range of 1%-99% in water or an organic solvent, or can be in pure (100%) form. One embodiment of the monomers used to form the second network can be described by the following characteristics: (1) it is capable of swelling without dissolving the polyurethane, (2) it is capable of polymerization, and (3) it contains carboxylic acid groups.

[0094] Other embodiments use additional comonomers that can be non-ionic, such as acrylamide, methacrylamide, N-hydroxyethylacrylamide, N-isopropylacrylamide, methyl methacrylate, N,N-dimethylacrylamide, N-vinylpyrrolidone, 2-hydroxyethyl methacrylate, 2-hydroxyethyl acrylate, or derivatives thereof.

[0095] In the presence of any of the above first networks, any type of compatible crosslinking agent can be used to crosslink the second network, such as ethylene glycol dimethacrylate, ethylene glycol diacrylate, diethylene glycol dimethacrylate (or diacrylate), triethylene glycol dimethacrylate (or diacrylate), tetraethylene glycol dimethacrylate (or diacrylate), polyethylene glycol dimethacrylate or polyethylene glycol diacrylate, methylene bisacrylamide, N,N'-(1,2-dihydroxyethylene) bisacrylamide, derivatives thereof, or combinations. Depending on its solubility in the precursor solution / material, any number of photoinitiators can also be used. These include (but are not limited to) 2-hydroxy-2-methyl-propiophenone and 2-hydroxy-1-[4-(2-hydroxyethoxy)phenyl]-2-methyl-1-propanone. Additionally, other initiators can be used, such as benzoyl peroxide, 2-oxoglutaric acid, azobisisobutyronitrile, or potassium persulfate (or sodium persulfate). For example, benzoyl peroxide can be used for temperature-initiated polymerization, while azobisisobutyronitrile and sodium persulfate can be used as free radical initiators.

[0096] In another embodiment, a solvent can be used as a mediator to transport monomers that would otherwise not mix (or dissolve in) the polymer to one (or more) phases of the polymer. The solvent must be carefully selected based on the specific masses and phases of the polymer and the monomer. For example, acetic acid can swell but not dissolve many polyurethanes. Thus, acetic acid can be used to carry other monomers (such as acrylamide solution) that would otherwise not enter the polyurethane into the bulk of the polyurethane. This allows acrylamide to selectively polymerize within one phase of the polyurethane. The acetic acid can then be washed away, leaving behind a polyurethane with one or more new properties. Other solvents that can be used include (but are not limited to) methanol, propanol, butanol (or any alkyl alcohol), acetone, dimethylacetamide, tetrahydrofuran, diethyl ether, or combinations thereof. Solvents with different degrees of swelling can be selected considering solubility in the polymer phase. The solubility of the solvent and the components of the material to be swollen can be obtained from polymer textbooks (such as The Polymer Handbook) or can be measured experimentally.

[0097] After polymerization of monomers containing carboxylic acid groups, any optional comonomers, and any crosslinking agents, the resulting composition is then reacted with one or more sulfonic acid-containing compounds to sulfonate a portion of the monomers containing carboxylic acid groups, thereby completing the second network. In certain embodiments, 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholine chloride is used as a catalyst to effect sulfonation of a precursor IPN or semi-IPN having carboxylic acid groups by amidation reaction with taurine. The chemical reaction process for producing a mixed anion IPN or semi-IPN is as shown Figure 1 . The sulfonation chemistry for converting carboxylic acid groups to sulfonate groups is as shown Figure 2 . Of course, the method is not limited to PAA, but also applies to virtually any polymer containing carboxylic acid groups.

[0098] In applications of the present disclosure include producing hydrophilic lubricious wall panels or coatings to reduce biofilm formation and / or barnacle formation in marine vessels, other watercraft or waterborne objects, or pipes. Additionally, the present disclosure can be used as a method for manufacturing supports and moving parts for applications such as engines, pistons, or other machines or machine parts. The present disclosure can also be used in long-term implants in artificial joint systems or other areas of the body, such as stents and catheters for blood vessels or the urinary tract, or implants, patches, or dressings for the skin.

[0099] The present disclosure can be used to generate a composition gradient within a starting homogeneous polymeric material. A gradient can be formed in the material along the thickness direction, where a mixed anionic IPN or semi-IPN is formed on one side and extends with a gradually decreasing concentration to the other side, for example, substantially only the starting polymeric material. The mixed anionic IPN or semi-IPN concentration gradient can be radial within the material, with the outer surface having the highest concentration of the mixed anionic IPN or semi-IPN and the center or core having the lowest concentration of the mixed anionic IPN or semi-IPN. In one method of making the thermoplastic gradient mixed anionic IPN or semi-IPN of the present disclosure, one side of a thermoplastic material is made to absorb a monomer solution as well as a photoinitiator and a crosslinker, and then the monomers are polymerized and crosslinked (e.g., with UV light) within the thermoplastic material to form a gradient mixed anionic IPN or semi-IPN. In one embodiment, a mixed anionic IPN or semi-IPN can be generated in a gradient hydrophobic polymer if it is only swollen on one side in a monomer containing carboxylic acid or if the swelling time is limited such that monomer diffusion through the bulk of the hydrophobic polymer is incomplete. This is particularly useful in generating osteochondral grafts for orthopedic joint replacement materials. For example, in the case of a cartilage replacement material, one side of the material is lubricated and water swollen while the other side remains solid (pure thermoplastic material). Alternatively, if the diffusion of the carboxylic acid-containing monomer into the hydrophobic polymer is precisely controlled by timed infiltration of the monomer into the bulk, a bulk material with the appearance of a mixed anionic IPN or semi-IPN and a "core" of only the hydrophobic polymer can be made. The differential swelling caused by this configuration can lead to residual stresses (compressive stress on the swollen side and tensile stress on the non-swollen side), which can contribute to enhancing the mechanical and fatigue behavior of the material. In the case of a material having a thickness gradient, the substrate of the material of only the hydrophobic polymer can be used to anchor, adhere, or suture the device to the target anatomical area. The substrate can be confined to a small area or be large (e.g., a skirt) and can extend outward as a single component or multiple components (e.g., straps). The internal stresses accumulated within the thermoplastic material during processing or after swelling can be reduced by temperature-induced annealing. For example, a temperature of 60 - 120 degrees Celsius can be used for various times (30 minutes - many hours) to anneal the polymer, and the heat can be applied in an oven, by a hot surface, by radiation, or by a heat gun. The thermoplastic material can subsequently be crosslinked using, for example, gamma or electron beam radiation.

[0100] Articles made from the hybrid anion IPNs and semi-IPNs of the present disclosure can also be formed in a laminated structure. In one example, the hybrid anion IPN or semi-IPN structure comprises a hydrophilic polymer such as sulfonated polyacrylic acid (sPAA) that is interpenetrated with a first thermoplastic material such as a polyether-based polyurethane formed over a second thermoplastic material such as a polycarbonate-based polyurethane. The first and second thermoplastic materials themselves can comprise multiple layers of various hardnesses and properties. Additionally, more than two thermoplastic material layers can be used, and one or more of the thermoplastic materials can be crosslinked. Finally, non-thermoplastic elements can be incorporated into the construct.

[0101] Heat can be used to re-anneal the physical crosslinks in the hydrophobic polymer side of the gradient hybrid anion IPN or semi-IPN (e.g., the hard segments in a polyurethane), resulting in different desired curvatures after bending (e.g., over a mold or template) and cooling, including both convex and concave curvatures on the hydrophobic polymer side of the gradient hybrid anion IPN or semi-IPN. Of course, other shapes can be formed as needed. Using a thermoplastic material as the hydrophobic polymer facilitates molding the device into the desired shape by, for example, injection molding, reaction injection molding, compression molding, or dip casting. The molded device can then undergo subsequent network infiltration and polymerization steps to produce a new hybrid anion IPN or semi-IPN material.

[0102] The shaping of the hybrid anion IPN and semi-IPN articles of the present disclosure can be performed in situ, such as within the human body, for example, by heating the thermoplastic hybrid anion IPN or semi-IPN so that it can wrap around the curvature of the femoral head or so that it can conform to the curvature of the acetabulum.

[0103] The shaped or unshaped hybrid anion IPN and semi-IPN articles made according to the present disclosure can be attached to other surfaces. For example, an adhesive such as a solvent, cement, or glue can be used to attach a thermoplastic gradient hybrid anion IPN or semi-IPN article to the surface of an adhesive interface. For example, the addition of a solvent causes local dissolution of the material, and after contacting the surface and drying the solvent, the thermoplastic material adheres to the surface. This method can be used to attach a gradient hybrid anion IPN or semi-IPN to the bone surface in a joint. In certain embodiments, the adhesive can be sterile in a disposable syringe.

[0104] In certain embodiments, the adhesive may include dimethacrylate carbamate and methyl methacrylate (MMA). A photoinitiator may be used to cure the adhesive with radiation such as visible light, infrared light, or ultraviolet light; it may be cured using a thermal initiator, chemical initiator, or catalyst and / or a redox-activated initiation system, such as a system comprising camphorquinone and N,N-dimethyl-p-toluidine. A combination of photoinitiation and non-photo-based initiation systems (such as thermal, chemical, and / or redox systems) may be used. Accelerators may also be used. The dimethacrylate carbamate may include soft segments selected from, for example, polyalkylene oxides (such as polyethylene oxide (PEO), polypropylene oxide (PPO), and polybutylene oxide (PBO)), polybutadiene, polydimethylsiloxane (PDMS), polyethylene adipate, polycaprolactone, polytetramethylene glycol adipate, polyisobutylene, polyhexamethylene carbonate diol, and poly(1,6-hexyl 1,2-ethyl carbonate). The dimethacrylate carbamate may include, for example, hard segments formed from 1,5-naphthalene diisocyanate (NDI), isophorone diisocyanate (IPDI), 3,3-dimethylbiphenyl diisocyanate (TODI), methylene bis(p-cyclohexyl isocyanate) (H 12 MDI), cyclohexyl diisocyanate, 2,6-toluene diisocyanate, or 2,4-toluene diisocyanate (TDI), hexamethylene diisocyanate, or methylene bis(p-phenyl isocyanate). The dimethacrylate carbamate component may include, for example, about 70-90% by weight of the adhesive.

[0105] Generally, in one embodiment, a system is provided that includes an article comprising the hybrid anionic IPN or semi-IPN of the present disclosure and an adhesive kit comprising an adhesive (such as a solvent, cement, or glue).

[0106] Generally, in one embodiment, a packaged article is provided that includes an article comprising the hybrid anionic IPN or semi-IPN of the present disclosure. In some embodiments, a solution containing divalent cations containing one or more divalent metal cations is contained within a sterile package.

[0107] This and other embodiments may include one or more of the following features. The adhesive kit may include a first reservoir containing a first mixture that includes at least one of a dimethacrylate carbamate oligomer and a methyl methacrylate monomer, at least one of a photoinitiator and a thermal initiator, and an inhibitor; a second reservoir containing a second mixture that includes at least one of a dimethacrylate carbamate monomer and a methyl methacrylate monomer and an accelerator; and instructions for use; wherein at least one of the first reservoir and the second reservoir may include a dimethacrylate carbamate monomer, and at least one of the first reservoir and the second reservoir may include a methyl methacrylate monomer.

[0108] Both the first reservoir and the second reservoir may contain dimethacrylate monomers and methyl methacrylate monomers. The second reservoir may further contain an inhibitor. The system may further contain polymethyl methacrylate. The system may further include a third reservoir containing polymethyl methacrylate powder. The first mixture, the second mixture, and the polymethyl methacrylate may define the component weights, and the weight of the polymethyl methacrylate powder may account for about 1% - about 70% of the component weights. The system may further contain polystyrene. The system may further contain a photoinitiator and a thermal initiator. The first reservoir may include a first chamber in a syringe, and the second reservoir may include a second chamber in the syringe, where the syringe may be configured to combine the first mixture and the second mixture to produce an adhesive mixture. The system may further include a nozzle connected to the syringe and configured to dispense the adhesive mixture. The first reservoir and the second reservoir may each contain about 0% (w / w) - about 100% (w / w), generally about 1% (w / w) - about 99% (w / w) of dimethacrylate oligomers and / or 0% (w / w) - about 100% (w / w), generally about 1% (w / w) - about 99% (w / w) of methyl methacrylate. The first reservoir and / or the second reservoir may each contain about 0% (w / w) - up to about 100% (w / w), generally about 1% (w / w) - up to about 99% (w / w) of methyl methacrylate. At least one initiator may include a photoinitiator containing between 0% (w / w) - about 5% (w / w), generally about 1% (w / w) - about 5% (w / w) of camphorquinone. At least one initiator may include a thermal initiator containing between 0% (w / w) - about 5% (w / w), generally about 1% (w / w) - about 5% (w / w) of benzoyl peroxide. The accelerator may include between 0% (w / w) - about 5% (w / w), generally about 1% (w / w) - about 5% (w / w) of N,N-dimethyl-p-toluidine. The inhibitor may include between 0% (w / w) - about 5% (w / w), generally about 1% (w / w) - about 5% (w / w) of hydroquinone. The system may further contain an additive configured to prevent infection. The system may further contain an antibiotic. The system may further contain a radiopaque material. The first mixture may define a viscosity between about 1 Pa.s - 5000 Pa.s.

[0109] In one embodiment, the adhesive kit may consist of a single reservoir containing from about 0% (w / w) to about 100% (w / w), generally from about 1% (w / w) to about 99% of a dimethacrylate carbamate oligomer and / or from 0% (w / w) to about 100% (w / w), generally from about 1% (w / w) to about 99% (w / w) of methyl methacrylate; from about 0% (w / w) to about 100% (w / w), generally from about 1% (w / w) to about 99% (w / w) of methyl methacrylate; an optional initiator (which may include, for example, at least one of a photoinitiator and a thermal initiator, the amount of which is generally from about 0% (w / w) to about 5% (w / w), such as from about 1% (w / w) to about 5% (w / w)) and an optional accelerator (the amount of which is generally from about 0% (w / w) to about 5% (w / w), such as from about 1% (w / w) to about 5% (w / w)). The single reservoir may include a chamber in a syringe. The system may further include a nozzle connected to the syringe configured to dispense the curable adhesive. The initiator may include a photoinitiator comprising between 0% (w / w) and about 5% (w / w), generally from about 1% (w / w) to about 5% (w / w) of camphorquinone. The accelerator may include between 0% (w / w) and about 5% (w / w), generally from about 1% (w / w) to about 5% (w / w) of N,N-dimethyl-p-toluidine. The inhibitor may include between 0% (w / w) and about 5% (w / w), generally from about 1% (w / w) to about 5% (w / w) of hydroquinone. The system may further comprise an additive configured to prevent infection. The system may further comprise an antibiotic. The system may further comprise a radiopaque material. The first mixture may be defined as having a viscosity between about 1 Pa·s and 5000 Pa·s.

[0110] The hybrid anionic IPN and semi-IPN compositions of the present disclosure, formed, for example, by the methods of the present disclosure, can be used in a variety of environments. One particular use is as artificial cartilage in osteochondral grafts. The present disclosure provides osteoprotective arthroplasty devices based on interpenetrating polymer networks that mimic the molecular structure of natural cartilage and, in turn, its elastic modulus, fracture strength, and lubricated surface. Mimicking at least some of these structural and functional aspects of natural cartilage, the hybrid anionic semi-IPN and anionic IPN of the present disclosure form the basis for a novel osteoprotective "biomimetic surface remodeling" arthroplasty. Designed to replace only the cartilage, this device is fabricated as a set of flexible implantable devices characterized by a lubricated joint surface and an osseointegratable bone interface.

[0111] In principle, the device can be made for any joint surface in the body. For example, a device covering the tibial plateau will require similar bone preparation and polymer shaping methods. For a device covering the femoral head in the hip joint, a cap-shaped device fits closely over the contour of the femoral head. For a device lining the inside of the acetabulum, a hemispherical cup-shaped device can extend at the edge and snap into place in the socket to provide a mating surface with the femoral head. In this way, both sides of the patient's hip joint can be repaired, creating a cap-on-cap joint connection. However, if only one of the surfaces is damaged, only one side may be covered, thus creating a cartilage-on-cap joint connection. Additionally, the materials of the present disclosure can be used to cover or line the articulating surfaces of another joint replacement or surface resurfacing device (generally including metal) to serve as an alternative bearing surface.

[0112] To use the present disclosure to create a cap-shaped device for the shoulder joint (also a ball-and-socket joint), a method similar to that of the hip joint is used. For example, a shallow cup can be created to line the glenoid fossa. Additionally, this "capping" concept can also be used to create devices for other joints in the hand, fingers, elbow, ankle, foot, and intervertebral facets. In one embodiment, in the distal femur, the volume of the distal femur device follows the contour of the bone while protecting the anterior and posterior cruciate ligaments.

[0113] As described below, the hybrid anion IPNs and semi-IPNs of the present disclosure can be used as cartilage replacement plugs in body joints where cartilage is damaged.

[0114] For example, the hybrid anion IPNs and semi-IPNs of the present disclosure made according to the methods of the present disclosure can be used as fully or partially synthetic osteochondral grafts. The osteochondral grafts consist of a lubricious cartilage-like synthetic support layer that can be anchored to porous bone or a synthetic porous bone-like structure. The support layer has two regions: a lubricious surface layer and a rigid bone anchoring layer. In one embodiment, the top lubricious region of the support layer consists of an interpenetrating polymer network composed of two polymers. The first polymer can be a hydrophobic thermoplastic material with high mechanical strength, including (but not limited to) polyether-based polyurethanes, polycarbonate-based polyurethanes, silicone polyether-based polyurethanes, and silicone polycarbonate-based polyurethanes, or these materials with incorporated urea linkages, or these materials with incorporated urea linkages (e.g., polyurethane ureas). The second polymer can be a hydrophilic polymer derived from monomers containing carboxylic acid groups (including (but not limited to) acrylic acid), which are subsequently subjected to a sulfonation process, in which the monomers containing carboxylic acid groups are reacted with a compound containing sulfonic acid. The bottom region of the support layer (bone anchoring layer) can be a rigid non-absorbable thermoplastic material that can be made to flow by ultrasonic welding vibrations, ultrasonic energy, laser energy, heat, RF energy, and electrical energy. The bone anchoring layer is used to anchor the support layer to bone or a bone-like porous structure. If porous bone is used, it can be cancellous bone of a human or an animal. If a synthetic bone-like material is used, it can be composed of porous calcium phosphate (and / or other materials, including (but not limited to) porous carbonated apatite, β-tricalcium phosphate, or hydroxyapatite) or a porous absorbable or non-absorbable thermoplastic material as described above (including (but not limited to) polycarbonate-based polyurethanes, polyether-based polyurethanes, PLA, PLLA, PLAGA, and / or PEEK). The support layer is anchored to the porous bone or bone-like structure by applying a combination of pressure and energy that causes the bone anchoring material to melt and flow into the pores or spaces of the bone or bone-like structure, after which the energy source is removed and the material is re-cured. The energy source can include (but not limited to) vibrations, ultrasonic energy, laser energy, heat, RF energy, and electrical energy.

[0115] In various embodiments, the compositions of the present disclosure can be used to form devices to partially or completely resurface damaged joint surfaces in the body of a mammal (animal or human). These devices can be fixed to bone in any number of ways, such as press-fit, screws (metal or plastic, absorbable or non-absorbable), sutures (absorbable or non-absorbable), glue, adhesives, photo-curable adhesives (e.g., based on polyurethane or resin), or cements (such as polymethyl methacrylate or calcium phosphate or dental cement).

[0116] Osteochondral graft implants formed from the disclosed mixed anion IPNs or semi-IPNs can be used to replace or augment cartilage within joints such as the hip or shoulder joint. The implant may slide over the head of the humerus or femur. In some embodiments, the implant may include an opening to receive a ligament or other anatomical structure.

[0117] According to the present disclosure, implants and other articles can be made in a variety of complex shapes. For example, an osteochondral graft can be formed from the disclosed mixed anion IPN or semi-IPN, which can be used alone or in any combination required to replace or augment cartilage within the knee joint. For example, the osteochondral graft can be adapted to engage the femoral condyles (or only one condyle), can be adapted to engage one or both sides of the tibial plateau, can be adapted to engage the patella and articulate with an osteochondral graft adapted to engage the patellofemoral groove, and / or can be adapted to engage the lateral and medial menisci.

[0118] Osteochondral grafts can also be used in other joints such as the fingers, hand, ankle, elbow, foot, or vertebrae. A glenoid prosthesis can be formed from the disclosed mixed anion IPN or semi-IPN for use in replacing or resurfacing the glenoid of the shoulder or hip. The disclosed mixed anion IPN or semi-IPN can be used as a bursa osteochondral graft, a glenoid osteochondral graft, a glenoid fossa osteochondral graft, and a humeral head osteochondral graft. In some embodiments, the disclosed mixed anion IPN or semi-IPN can be used as a prosthesis for resurfacing the intervertebral facet.

[0119] The disclosed mixed anion IPN and semi-IPN compositions can be formed as a prosthetic cartilage plug for partial surface resurfacing of a joint surface. For example, the prosthetic cartilage plug can be formed from the disclosed gradient mixed anion IPN composition. The plug can have a stem portion that is formed on the thermoplastic material side of the article and is adapted to be inserted into a hole or opening in bone. As described above, the head of the plug is formed as a lubricious mixed anion IPN or semi-IPN. The stem can be press-fit into a hole or opening in bone such that the lubricious mixed anion IPN surface is exposed to function as prosthetic cartilage.

[0120] A prosthetic cartilage plug is formed from the disclosed mixed anion IPN or semi-IPN, wherein the stem is provided with helical ridges to form a screw for securing the plug to bone.

[0121] Embodiments of the disclosed compositions can be used to prepare bilaterally lubricious implants. The implant can be sized and configured to replace an intervertebral disc. The implant can have lubricious mixed anion IPN or semi-IPN surfaces on its upper and lower sides (e.g., formed as described above). A knee spacer having a wedge-shaped cross-section can be formed. Like the intervertebral disc prosthesis, the spacer also has lubricious mixed anion IPN or semi-IPN surfaces on its upper and lower sides.

[0122] The following describes other variations and modifications of the above compositions, articles, and methods.

[0123] The hydrophobic polymer can be a commercially available or custom-made polymer and can be made by various methods such as extrusion, injection molding, compression molding, reaction injection molding (RIM), or solution casting. The first polymer can be uncrosslinked or crosslinked by various means. Either of the two polymers can be crosslinked by, for example, γ-radiation or electron beam radiation.

[0124] Any number or combination of ethylenically unsaturated monomers or macromonomers (e.g., containing reactive double bonds) can be used as the basis for the second or subsequent networks, provided that monomers containing carboxylic acid groups are included. These monomers include (but are not limited to) those containing vinyl, acrylate, methacrylate, allyl ether, or acrylamide groups. Any number of side-chain functional groups can be conjugated to these ethylenically unsaturated groups, including (but not limited to) carboxylic acid, ester, alcohol, ether, phenol, aromatic group, or carbon chain.

[0125] The hydrophobic polymer can be a polyurethane-based polymer such as the following polymers: polyether-based polyurethane, polycarbonate-based polyurethane, polyurethane urea, silicone polyether-based polyurethane, or silicone polycarbonate-based polyurethane. Other polyurethanes with other hard segments, soft segments, and chain extenders are also possible.

[0126] Other polymers can be used as the hydrophobic polymer, such as silicone ((polydimethylsiloxane) or homopolymers or copolymers of polyethylene.

[0127] When a polyurethane-based polymer is used as the hydrophobic polymer, the degree of physical and chemical crosslinking of the polyurethane-based polymer can vary between only physical crosslinking (thermoplastic) and extensive chemical crosslinking. In the case of chemical crosslinking, the crosslinkable polyurethane can be used alone or as a mixture with thermoplastic (uncrosslinked) polyurethane.

[0128] The polymerization conditions (i.e., ambient oxygen, UV intensity, UV wavelength, exposure time, temperature) and sulfonation conditions can vary.

[0129] The orientation and steepness of the composition gradient can be varied by various means, such as the time and / or method of immersion in monomers and / or amino sulfonic acid compounds and the application of external hydrostatic positive or negative pressure.

[0130] The hydrophobic polymer can be made porous by various techniques such as foaming or salt leaching. After swelling the porous polymer (e.g., PU) with a monomer (e.g., AA), followed by polymerization or reaction of AA with amino sulfonic acid, a porous mixed anionic IPN is formed.

[0131] Additional thermoplastic material layers can be added to the material by curing or drying a new thermoplastic material onto the surface, either only on the IPN side or on the thermoplastic material side. These layers can all be the same material or different materials (such as ABS + polyurethane, polyether-based polyurethane + polycarbonate-based polyurethane, etc.).

[0132] Many different solvents can be used during the synthesis of the polyurethane, the second network, or both, including (but not limited to) dimethylacetamide, tetrahydrofuran, dimethylformamide, ethanol, methanol, acetone, water, dichloromethane, propanol, methanol, or combinations thereof.

[0133] Any number of coupling reagents can be used to facilitate the reaction of the sulfamic acid compound with the polymer containing a carboxylic acid group, including triazine-based coupling reagents, carbodiimides, phosphorus and amines salts, as well as fluorinated formamidines coupling reagents. In one particular embodiment, the coupling reagent can be 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholine chloride (DMTMM).

[0134] The degree and depth of derivatization (i.e., sulfonation) of solid articles containing a precursor polymer with carboxylic acid groups (including PAA-based IPNs) depend on the balance between the diffusion rate of the reactants and the reaction kinetics and hydrolysis rate of the coupling reagent and the intermediate ester. A class of coupling reagents that has been widely used for the activation and derivatization of carboxylic acids in aqueous solutions is carbodiimides. In various embodiments, an amino sulfonic acid compound such as taurine is first diffused into the PAA-based IPN, and then an N-substituted carbodiimide is added. The N-substituted carbodiimide reacts with the carboxylic acid to form a highly reactive O-acylisourea intermediate, which is pH-dependent and prone to hydrolysis within seconds at near physiological pH (Hoare, DG. and Koshland, DEJ. (1967) ‘A method for the quantitative modification and estimation of carboxylic acid groups in proteins’, Journal of Biological Chemistry, 242(10), pp. 2447-2453). After hydrolysis, the intermediate ester is converted back to the carboxylic acid and an inactive N-acylurea. This immediate hydrolysis effectively consumes the coupling reagent before it can diffuse within the bulk of the IPN and react with the primary amine of the amino sulfonic acid compound. Lowering the pH can decrease the hydrolysis rate of the intermediate ester, but the hydrolysis of the unreacted coupling reagent is accelerated under acidic conditions (Gilles, MA., Hudson, AQ. and Borders, CL. (1990) ‘Stability of water-soluble carbodiimides in aqueous solution’, Analytical Biochemistry. Academic Press, 184(2), pp. 244-248). Additionally, the diffusibility of the coupling reagent is decreased under acidic conditions because the IPN loses its water content and its permeability decreases. Since the coupling reagent is consumed on the surface of the IPN, this leads to further inhibition of the bulk reaction. In summary, molecules that are unstable in aqueous solution or form intermediate esters that are prone to hydrolysis at physiological pH cannot effectively derivatize the bulk of PAA-based IPNs, and the modification remains confined to the surface of the IPN.

[0135] The various properties of IPN under physiological conditions, including lubricity, depend on the bulk derivation of the material. The inventors have found that IPN modification to a depth greater than a certain level can only be achieved under the following conditions: a) the coupling reagent is water-soluble and not labile under aqueous conditions, b) the intermediate ester is stable at physiological pH, and c) the diffusion rate of the reactants is sufficient to allow the reaction to occur before hydrolysis of the intermediate ester. Triazine-based coupling reagents, such as CDMT or DMTMM, are stable under aqueous conditions and have been used to derivatize large sugars, such as hyaluronan (D'este M, Eglin D, Alini M, (2014), `A systematic analysis of DMTMM vs EDC / NHS for ligation of amines to Hyaluronan in water’, Carbohydrate Polymers, vol:108 pp:239-246). The conversion rate of the reaction with DMTMM, where all reactants are in solution, can be higher than that of carbodiimide. In this embodiment, the reaction conditions can be adjusted to allow the reactants to diffuse effectively before hydrolysis of the intermediate ester formed between the triazine-based compound and the carboxylic acid groups of the secondary network of IPN. Since the reaction is limited by the rates of diffusion and ester hydrolysis, the depth of the reaction can be controlled by varying the pH, by varying the reaction time, by adding the coupling reagent, or a combination of any two or all three of the above. The pH enables control of the permeability of IPN and the reactivity / hydrolysis rate of the intermediate ester. The reaction time enables control of the amount of time required for the reactants to diffuse and react within the material bulk. The controlled addition of the coupling reagent enables the coupling reagent to be added at the same rate as the overall reaction rate, which combines reagent diffusion and reaction with hydrogel swelling. By adjusting these parameters, derivatization of IPN can be achieved at depths ranging from a few micrometers to several hundred micrometers or throughout the entire depth of the material.

[0136] Any number of initiators can be used, such as photoinitiators (e.g., compounds containing phenone), thermal initiators, or chemical initiators. Examples of thermal initiators include (but are not limited to) azo compounds, peroxides (e.g., benzoyl peroxide), persulfates (e.g., potassium persulfate or ammonium persulfate), their derivatives, or combinations.

[0137] Crosslink identity and density (e.g., 0.0001% - 25% based on the molar crosslinker relative to the monomer), initiator concentration (e.g., 0.0001% - 0% based on the molar ratio relative to the monomer), molecular weight of the precursor polymer, relative polymer weight percentage, light wavelength (UV to visible range), light intensity (0.01 mW / cm 2 -5 W / cm 2) Changes in temperature, pH, ionic strength of the swelling solution, and degree of hydration.

[0138] The second network material can be synthesized in the absence of a crosslinking agent.

[0139] The water content of these materials can range between 2% and 99%.

[0140] The different components of the mixed anionic IPN can be incorporated in combination with monomers containing carboxylic acid groups (such as vinyl alcohol, ethylene glycol acrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, acrylamide, N-isopropylacrylamide, dimethylacrylamide, and their combinations or derivatives). Any monomer or combination of monomers can be used together with a suitable solvent, as long as it includes monomers containing carboxylic acid groups and can penetrate (swell) the first polymer.

[0141] The mixed anionic IPN can incorporate certain additives, such as antioxidants (e.g., vitamin C, vitamin E, or santowhite powder) and / or antimicrobial agents (e.g., antibiotics), either chemically or physically within its bulk or on its surface. These can be chemically linked to the material, for example, through the esterification of antioxidants with any vinyl-containing monomer such as methacrylate, acrylate, acrylamide, vinyl, or allyl ether.

[0142] More than two networks (e.g., three or more) can also be formed, each of which can be crosslinked or uncrosslinked.

[0143] Other modifications will be apparent to those skilled in the art.

[0144] Other aspects of the present disclosure are shown in the following paragraphs.

[0145] Aspect 1. An implant comprising an ionic polymer containing undervivatized carboxylic acid groups and sulfamic acid-derived carboxylic acid groups.

[0146] Aspect 2. The implant of Aspect 1, wherein the underivatized carboxylic acid groups correspond to one or more of the following: undervivatized acrylic monomers within the ionomer, undervivatized methacrylic monomers within the ionomer, undervivatized crotonic acid monomers within the ionomer, undervivatized linolenic acid monomers within the ionomer, undervivatized maleic acid monomers within the ionomer, and undervivatized fumaric acid monomers within the ionomer, and wherein the sulfamic acid-derived carboxylic acid groups correspond to one or more of the following: sulfamic acid-derived acrylic monomers within the ionomer, sulfamic acid-derived methacrylic monomers within the ionomer, sulfamic acid-derived crotonic acid monomers within the ionomer, sulfamic acid-derived linolenic acid monomers within the ionomer, sulfamic acid-derived maleic acid monomers within the ionomer, and sulfamic acid-derived fumaric acid monomers within the ionomer.

[0147] Aspect 3. The implant of any one of Aspects 1-2, wherein the implant comprises a measurable amount of the formula (H2N) x R(SO3H) y sulfamic acid compound or a salt thereof, wherein R is an organic moiety, x is a positive integer and y is a positive integer.

[0148] Aspect 4. The implant of Aspect 3, wherein R is a hydrocarbon moiety.

[0149] Aspect 5. The implant of Aspect 4, wherein the hydrocarbon moiety is an alkane moiety, an alkene moiety, an alkyne moiety, an aromatic moiety, or a hydrocarbon moiety having a combination of two or more of alkane, alkene, alkyne, and aromatic substituents.

[0150] Aspect 6. The implant of any one of Aspects 4-5, wherein the hydrocarbon moiety is a C1-C12 hydrocarbon moiety.

[0151] Aspect 7. The implant of any one of Aspects 1-2, wherein the implant comprises a measurable amount of a sulfamic acid compound selected from taurine and taurine derivatives.

[0152] Aspect 8. The implant of any one of Aspects 1-7, wherein the concentration of the undervivatized carboxylic acid groups and the concentration of the amino-sulfonic acid-derived carboxylic acid groups are substantially constant throughout the implant.

[0153] Aspect 9. The implant of any one of Aspects 1-7, wherein the concentration of the undervivatized carboxylic acid groups and / or the concentration of the amino-sulfonic acid-derived carboxylic acid groups vary by at least + / - 10% between two sites within the implant.

[0154] Aspect 10. An implant according to any one of aspects 1 - 7, wherein the implant comprises a gradient of the concentration of the underivatized carboxylic acid groups and / or a gradient of the concentration of the amino-sulfonic acid-derived carboxylic acid groups.

[0155] Aspect 11. The implant of aspect 10, wherein the concentration of the underivatized carboxylic acid groups decreases with an increase in the distance from at least one outer surface of the implant.

[0156] Aspect 12. The implant of aspect 10, wherein the concentration of the undervivatized carboxylic acid groups increases with an increase in the distance from at least one outer surface of the implant.

[0157] Aspect 13. The implant according to any one of aspects 10 - 12, wherein the concentration of the amino-sulfonic acid-derived carboxylic acid groups decreases with an increase in the distance from at least one outer surface of the implant.

[0158] Aspect 14. The implant according to any one of aspects 10 - 12, wherein the concentration of the amino-sulfonic acid-derived carboxylic acid groups increases with an increase in the distance from at least one outer surface of the implant.

[0159] Aspect 15. The implant according to any one of aspects 1 - 14, wherein the molar ratio of the amino-sulfonic acid-derived carboxylic acid groups to the undervivatized carboxylic acid groups varies by at least + / - 10% between two sites in the implant.

[0160] Aspect 16. The implant according to any one of aspects 1 - 14, wherein the molar ratio of the amino-sulfonic acid-derived carboxylic acid groups to the undervivatized carboxylic acid groups decreases with an increase in the distance from at least one outer surface of the implant within the implant.

[0161] Aspect 17. The implant according to any one of aspects 1 - 14, wherein the molar ratio of the amino-sulfonic acid-derived carboxylic acid groups to the undervivatized carboxylic acid groups increases with an increase in the distance from at least one outer surface of the implant within the implant.

[0162] Aspect 18. The implant according to any one of aspects 1 - 14, wherein the molar ratio of the amino-sulfonic acid-derived carboxylic acid groups to the undervivatized carboxylic acid groups varies between one surface of the implant and the opposite surface of the implant.

[0163] Aspect 19. The implant according to any one of aspects 1 - 18, wherein the implant comprises an interpenetrating or semi-interpenetrating polymer network, the network comprising a first polymer network containing a first polymer and a second polymer network containing the ionomer.

[0164] Aspect 20. The implant of aspect 19, wherein the first polymer is a hydrophobic polymer.

[0165] Aspect 21. An implant of any one of aspects 19 - 20, wherein the first polymer is a thermoplastic polymer.

[0166] Aspect 22. An implant of any one of aspects 19 - 21, wherein the first polymer is a polyurethane.

[0167] Aspect 23. The implant of aspect 22, wherein the polyurethane is a polyether - type polyurethane.

[0168] Aspect 24. An implant of any one of aspects 1 - 23, wherein the implant is configured to repair or replace cartilage in a joint within the body.

[0169] Aspect 25. The implant of aspect 24, wherein the joint within the body is selected from the group consisting of knee joint, condyle, patella, tibial plateau, ankle joint, elbow joint, shoulder joint, finger joint, thumb joint, glenoid cavity, hip joint, intervertebral disc, zygapophyseal joint, upper lip, meniscus, metacarpophalangeal joint, metatarsophalangeal joint, phalangeal joint, temporomandibular joint, and wrist joint, including parts thereof.

[0170] Aspect 26. A method comprising reacting a solid article comprising a precursor polymer containing underivatized carboxylic acid groups with an amino - sulfonic acid compound such that an amide bond is formed between the carboxylic acid groups of the precursor polymer and the amine groups of the amino - sulfonic acid compound.

[0171] Aspect 27. The method of aspect 26, wherein the amino - sulfonic acid compound is of the formula (H2N) x R(SO3H) y or a salt thereof, wherein R is an organic moiety, x is a positive integer and y is a positive integer.

[0172] Aspect 28. The method of aspect 26, wherein R is a hydrocarbon moiety.

[0173] Aspect 29. The method of aspect 28, wherein the hydrocarbon moiety is an alkane moiety, an alkene moiety, an alkyne moiety, and an aromatic moiety or a hydrocarbon moiety comprising a combination of two or more of alkane, alkene, alkyne, or aromatic substituents.

[0174] Aspect 30. The method of any one of aspects 28 - 29, wherein the hydrocarbon moiety is a C1 - C12 hydrocarbon moiety.

[0175] Aspect 31. The method of aspect 26, wherein the amino - sulfonic acid is selected from taurine and taurine derivatives.

[0176] Aspect 32. The method of any one of aspects 26 - 31, comprising contacting the solid article with the amino - sulfonic acid compound such that the amino - sulfonic acid compound diffuses into the solid article.

[0177] Aspect 33. The method of aspect 32, further comprising contacting the solid article with a coupling reagent such that the coupling reagent diffuses into the solid article.

[0178] Aspect 34. The method of aspect 33, wherein the coupling reagent is diffused into the solid article before the sulfonic acid compound is diffused into the solid article, wherein the coupling reagent is diffused into the solid article after the sulfonic acid compound is diffused into the solid article, or wherein the coupling reagent and the sulfonic acid compound are diffused into the solid article simultaneously.

[0179] Aspect 35. The method of any one of aspects 33 - 34, wherein the coupling reagent is selected from triazine - based coupling reagents, carbodiimide coupling reagents, phosphonium salt coupling reagents, ammonium salt coupling reagents, and fluoroformamidine coupling reagents. salt coupling reagents, amine salt coupling reagents and fluoroformamidine coupling reagents.

[0180] Aspect 36. The method of any one of aspects 33 - 34, wherein the coupling reagent is 4-(4,6 - dimethoxy - 1,3,5 - triazin - 2 - yl)-4 - methylmorpholine chloride (DMTMM).

[0181] Aspect 37. The method of any one of aspects 26 - 36, wherein the precursor polymer is selected from polymers comprising one or more monomers selected from acrylic acid, methacrylic acid, crotonic acid, linolenic acid, maleic acid, and fumaric acid.

[0182] Aspect 38. The method of any one of aspects 26 - 37, wherein the solid article comprises an interpenetrating or semi - interpenetrating polymer network, the network comprising a first polymer network containing a first polymer and a second polymer network containing a precursor polymer.

[0183] Aspect 39. The method of aspect 38, wherein the first polymer is a hydrophobic polymer.

[0184] Aspect 40. The method of any one of aspects 38 - 39, wherein the first polymer is a thermoplastic polymer.

[0185] Aspect 41. The method of any one of aspects 38 - 40, wherein the first polymer is a polyurethane.

[0186] Aspect 42. The method of aspect 41, wherein the polyurethane is a polyether - type polyurethane.

[0187] Aspect 43. The method of any one of aspects 26 - 42, wherein the implant is configured to repair cartilage in a prosthetic joint replacement.

[0188] Aspect 44. The method of aspect 43, wherein the in vivo joint is selected from the group consisting of knee joint, condyle, patella, tibial plateau, ankle joint, elbow joint, shoulder joint, finger joint, thumb joint, glenoid cavity, hip joint, intervertebral disc, zygapophyseal joint, upper lip, meniscus, metacarpophalangeal joint, metatarsophalangeal joint, phalangeal joint, temporomandibular joint, and wrist joint, including parts thereof.

[0189] Aspect 45. An implant comprising an ionomer and a divalent cation-containing solution comprising one or more divalent metal cations, wherein the implant is at least partially immersed in the divalent cation-containing solution.

[0190] Aspect 46. The implant of aspect 45, wherein the implant and the divalent cation-containing solution are contained in a sterile package.

[0191] Aspect 47. The implant of any one of aspects 44-46, wherein the divalent cation-containing solution is a simulated body fluid containing physiological levels of ions found in synovial fluid.

[0192] Aspect 48. The implant of any one of aspects 44-47, wherein the divalent cation-containing solution comprises 0.1-5 mM total divalent metal cations.

[0193] Aspect 49. The implant of any one of aspects 44-48, wherein the divalent cation-containing solution comprises calcium ions, magnesium ions, or a combination of calcium ions and magnesium ions.

[0194] Aspect 50. The implant of any one of aspects 44-48, wherein the divalent cation-containing solution comprises calcium ions and magnesium ions.

[0195] Aspect 51. The implant of aspect 50, wherein the divalent cation-containing solution comprises 0.5-2.0 mM calcium ions.

[0196] Aspect 52. The implant of any one of aspects 50-51, wherein the divalent cation-containing solution comprises 0.2-1.5 mM magnesium ions.

[0197] Aspect 53. The implant of any one of aspects 44-52, wherein the divalent cation-containing solution further comprises a monovalent metal ion selected from the group consisting of sodium ions, potassium ions, or a combination of sodium and potassium ions.

[0198] Aspect 54. The implant of aspect 53, wherein the divalent cation-containing solution contains 0-300 mM total monovalent metal cations.

[0199] Aspect 55. The implant of any one of aspects 44-54, wherein the ionomer comprises carboxylic acid groups, sulfonic acid groups, or a combination of carboxylic acid groups and sulfonic acid groups.

[0200] Aspect 56. An implant of any one of aspects 44 - 54, wherein the ionomer comprises carboxylic acid groups and sulfonic acid groups.

[0201] Aspect 57. An implant of any one of aspects 44 - 56, wherein the implant comprises an interpenetrating or semi - interpenetrating polymer network, the network comprising a first polymer network containing a first polymer and a second polymer network containing the ionomer.

[0202] Aspect 58. The implant of aspect 57, wherein the first polymer is a hydrophobic polymer.

[0203] Aspect 59. The implant of any one of aspects 57 - 58, wherein the first polymer is a thermoplastic polymer.

[0204] Aspect 60. The implant of any one of aspects 57 - 59, wherein the first polymer is a polyurethane.

[0205] Aspect 61. The implant of aspect 60, wherein the polyurethane is a polyether - type polyurethane.

[0206] Aspect 62. The implant of any one of aspects 44 - 61, wherein the implant is selected to repair or replace cartilage in a joint in the body.

[0207] Aspect 63. The implant of aspect 62, wherein the joint is selected from the knee joint, condyle, patella, tibial plateau, ankle joint, elbow joint, shoulder joint, finger joint, thumb joint, glenoid cavity, hip joint, intervertebral disc, facet joint, upper lip, meniscus, metacarpophalangeal joint, metatarsophalangeal joint, phalangeal joint, temporomandibular joint, and wrist joint, including parts thereof. Examples

[0208] Example 1 The following description relates to a first exemplary embodiment of an interpenetrating ionomer composition, where polyether - type polyurethane serves as the first network and polyacrylic acid serves as the second polymer network. The IPN is synthesized in a two - step sequence: A test article made of polyether - type polyurethane is immersed in a 70% (w / w%) aqueous acrylic acid solution supplemented with 5000 ppm N,N’ - methylenebisacrylamide and 1000 ppm 2 - hydroxy - 2 - methylpropiophenone. The swollen article is polymerized under ultraviolet irradiation (40 mW / cm 2 ) for 13 minutes and then neutralized at a constant pH = 7.4. The final composition of the IPN contains 37 / 19 / 45 (wt%) of PEU, PAA, and H2O, respectively. The test article is incubated in a taurine (2 - aminoethanesulfonic acid) solution (320 mM) for 1 day, after which an equimolar amount of DMTMM (4 - (4,6 - dimethoxy - 1,3,5 - triazin - 2 - yl) - 4 - methylmorpholine Chloride). The test article was reacted for 48 hours and washed with a large amount of water for 4 days. This process is schematically illustrated in Figure 2 . After synthesis, the chemical composition was evaluated by elemental analysis (Table 1). The sulfonation yield of PAA was 50%. In addition, as Figure 4 shown, the penetration of the amidation reaction reached half (50%) or 1000 microns of the total thickness of the test article (i.e., a 2 mm thick sample). In other words, if both sides were involved in the diffusion of the reagent, the conversion could reach 100%, and the material would be functionalized throughout the thickness of the PAA-PEU network. In contrast, when using carbodiimide (such as EDC) under the same reaction conditions and reactant ratios, for a 2 mm thick sample, the penetration and functionalization of the PAA-PEU network did not exceed 20% in depth, or 400 microns. This difference in the coupling efficiency between EDC and the triazine coupling reagent has also been previously reported for the functionalization of hyaluronan large polymers under aqueous conditions (D'este M, Eglin D, Alini M, (2014), `A systematic analysis of DMTMM vs EDC / NHS for ligation of amines to Hyaluronan in water’, Carbohydrate Polymers, vol: 108 pp: 239-246).

[0209] The following description relates to a second exemplary embodiment of an interpenetrating ionic polymer composition, where a polyether-based polyurethane serves as the first network and polyacrylic acid serves as the second polymer network. The IPN was synthesized in two steps sequentially: A test article made of polyether-based polyurethane was immersed in a 60% (w / w%) aqueous acrylic acid solution supplemented with 5000 ppm N,N'-methylenebisacrylamide and 1000 ppm 2-hydroxy-2-methylpropiophenone. The swollen article was polymerized under ultraviolet irradiation (40 mW / cm 2 ) for 13 minutes and then neutralized at a constant pH = 7.4. The final composition of the IPN contained 48 / 17 / 35 (wt%) of PEU, PAA, and H2O, respectively. The test article was incubated in a taurine solution (320 mM) for 1 day, after which an equimolar amount of DMTMM was added. The test article was reacted for 48 hours and washed with a large amount of water for 4 days. After synthesis, the chemical composition was evaluated by elemental analysis (Table 1). The sulfonation yield of PAA was 29%.

[0210] The following description relates to a third exemplary embodiment of an interpenetrating ionic polymer composition, where a polyether-based polyurethane serves as the first network and polyacrylic acid serves as the second polymer network. The IPN is synthesized in a two-step sequence: A test article made of polyether-based polyurethane is immersed in a 50% (w / w%) aqueous acrylic acid solution supplemented with 2000 ppm of N,N'-methylenebisacrylamide and 2000 ppm of 2-hydroxy-2-methylpropiophenone. The swollen article is polymerized under ultraviolet irradiation (40 mW / cm 2 ) for 13 minutes and then neutralized at a constant pH = 7.4. The final composition of the IPN contains 57 / 16 / 26 (wt%) of PEU, PAA, and H2O, respectively. The test article is incubated in a taurine solution (320 mM) for 1 day, after which an equimolar amount of DMTMM is added. The test article is allowed to react for 48 hours and is washed with copious amounts of water for 4 days. After synthesis, the chemical composition is evaluated by elemental analysis (Table 1). The sulfonation yield of PAA is 26%.

[0211] Table 1. Composition of Exemplary Sulfonated Interpenetrating Networks Example 2 A gradient PEU-PAA formulation with PAA / PEU (w / w%) content ranging from 17.6% to 29.9% was synthesized by following a procedure similar to that described in Example 1. There is a linear relationship between the AA immersion solution and PAA / PEU (w / w%), which allows determination of the final PAA / PEU percentage based on the initial immersion solution. The results are shown in Table 2.

[0212] Table 2: Generation of Test Samples for Sulfonation and Testing Refers to the percentage of acrylic acid in water used to synthesize the gradient PEU-PAA test article.

[0213] The gradient PEU-PAA formulation was then sulfonated following a procedure similar to that of Example 1. The sulfonation percentage was characterized by the increase in dry and wet weights and elemental analysis to calculate the sulfur content and sulfonation conversion rate. The data are summarized in Table 3. The sulfur content was in the range of 0.5 - 2% and the sulfonation conversion rate was 9% - 31%.

[0214] Table 3: Weight Increase, Sulfur Content, and Sulfonation Conversion Rate of Sulfonated Gradient PEU-PAA The sulfonated gradient PEU-PAA material shows a higher tendency of weight increase after sulfonation, and the PAA / PEU w / w% increases, indicating that with the increase in PAA content, more carboxyl groups from PAA will react with taurine to introduce sulfonic acid groups. It is found that the weight increase (both wet weight and dry weight) of the sulfonated gradient PEU-PAA is a linear function of the PAA / PEU content. The increase in dry weight is believed to be caused by the addition of taurine molecules to the PAA backbone through the sulfonation reaction, while the increase in wet weight is believed to be caused by the ability of the sulfonated gradient PEU-PAA to retain water content.

[0215] Elemental analysis was performed to obtain the contents of carbon, nitrogen, hydrogen, and sulfur from the sulfonated test articles. This data was used to calculate the conversion rate of carboxyl groups to sulfonic acid groups. As can be seen from Table 3, the sulfur content / sulfonation conversion rate increases with the increase in the PAA / PEU percentage. This indicates that with the increase in the number of carboxyl groups per unit weight, more taurine can be attached.

[0216] The final synthesis step of the sulfonated gradient PEU-PAA test articles involves equilibration in simulated body fluid (SBF, 1.2 mM Ca 2+ , 0.6 mM Mg 2+ , 154 mM NaCl) before γ-irradiation. The final composition of all the synthesized materials after SBF equilibration was calculated and listed in Table 4 (highlighted in gray).

[0217] Table 4. Composition of sulfonated gradient PEU-PAA after equilibration in SBF The tensile, compressive, and tear properties of the sulfonated gradient PEU-PAA test articles were evaluated within a range of PAA contents. The data is summarized in Tables 5 - 7. To enable a direct comparison of the material properties between the gradient PEU-PAA formulations and the non-sulfonated gradient PEU-PAA formulations using a common variable, the PAA / PEU percentage was used as the independent variable for the following reasons: (a) the same sulfonation conditions were used for all synthesized materials regardless of their PAA / PEU (w / w%), (b) sulfonation is indirectly controlled by the level of PAA / PEU (w / w%) (see Table 3), and (c) materials synthesized with the same initial conditions have statistically similar mechanical properties regardless of the sulfonation process or sulfur content.

[0218] The tensile properties of all formulations are listed in Tables 5 and 5.1. It was found that the ultimate tensile strength (UTS) decreases with the increase in PAA / PEU w / w%. This is attributed to the increase in water content with the change in PAA / PEU w / w% (Table 3), resulting in a weaker material.

[0219] Table 5: Tensile strength of sulfonated gradient PEU-PAA and non-sulfonated gradient PEU-PAA.

[0220] Table 5.1 Tensile properties of sulfonated gradient PEU-PAA and non-sulfonated gradient PEU-PAA Similar trends were observed for all other tensile properties evaluated. Specifically, the ultimate true strain, which captures the maximum material elongation before failure, decreased with the variation of PAA / PEU w / w%, ranging from 223.8 ± 52.3% for the formulation with the lowest (17.6%) PAA / PEU w / w% to 95.2 ± 12.8% for the formulation with the highest (40.7%) (Table 5.1). The ultimate true strain of the non-sulfonated gradient PEU-PAA was 181.0 ± 32.7%, almost twice that of the sulfonated counterpart (95.2 ± 12.8%) with the same PAA / PEU w / w%. This is attributed to the fact that the sulfonated gradient PEU-PAA formulation with 40.7% PAA / PEU w / w% has more water (41.4% - see Table 3) than the non-sulfonated gradient PEU-PAA (36.7% - see Table 3). Additionally, a high variance in the ultimate true strain was observed, which is attributed to the randomness of material failure under tension affected by material and test article defects.

[0221] The tensile modulus (Young's modulus), which defines the relationship between stress and strain in the linear elastic region, decreased exponentially with the increase of PAA / PEU w / w%. The tensile modulus (32.5 ± 0.8 MPa) for the formulation with 40.7 (highest) PAA / PEU w / w% decreased significantly (p < 0.01) from the previous formulation with 30% PAA / PEU w / w% (48.4 ± 2.8 MPa), indicating a rapid decline in the tensile modulus above this threshold. Additionally, similar to the trends seen in the ultimate tensile strength and tensile strain, the tensile modulus of the non-sulfonated gradient PEU-PAA was higher than that of the sulfonated gradient PEU-PAA with the same PAA / PEU w / w% (46.4 ± 2.3).

[0222] Similar to the UTS, the tangent tensile modulus at 30% strain (see Table 5.1), which can be used to describe the behavior of materials where the stress has exceeded the elastic region and reached plastic deformation, decreases with increasing PAA / PEU w / w%. For the test article with the lowest (17.6%) PAA / PEU w / w%, the tangent tensile modulus was 37.1 ± 2.2 MPa, and for the formulation with the highest (40.7%) PAA / PEU w / w%, the tangent tensile modulus decreased to 24.6 ± 0.5 MPa. In contrast, the tangent tensile modulus of the non-sulfonated gradient PEU-PAA was 29.0 ± 0.35 MPa, indicating that when the material undergoes plastic deformation, the sulfonated and non-sulfonated formulations with the same PAA / PEU w / w% have similar deformation rates.

[0223] Taking all tensile properties into account, to obtain tensile properties similar to those of the non-sulfonated gradient PEU-PAA, a lower level of PAA can be used for the sulfonated gradient PEU-PAA compared to the non-sulfonated gradient PEU-PAA.

[0224] The compression properties of all formulations are listed in Tables 6 and 6.1. For the ultimate compression strength, all formulations are higher than the desired preliminary specification of 25.4 MPa. Even at high strains (> 60% of the true compression strain), none of the sulfonated gradient PEU-PAA samples failed under compression. Since the material does not fail under compression, there is no definite specific trend for the ultimate compression strength and the ultimate compression strain.

[0225] Table 6: Compression strength characteristics of sulfonated gradient PEU-PAA and non-sulfonated gradient PEU-PAA Table 6.1: Compression properties of sulfonated gradient PEU-PAA and non-sulfonated gradient PEU-PAA The compression strength of the non-sulfonated gradient PEU-PAA was 332.8 ± 16.7 MPa, which is higher than all sulfonated gradient PEU-PAA formulations. Since the material did not fail under compression, the compression strengths could not be directly compared, so the materials were re-evaluated in dynamic compression.

[0226] The compressive modulus (Young's modulus for compression), which measures the hardness of a solid material under compression in the linearly elastic region, is similar to the tensile modulus and decreases exponentially with increasing PAA / PEU w / w%. The compressive modulus gradually decreases from 111.1 ± 11.5 MPa for the formulation with the lowest (17.6) PAA / PEU w / w% to 50.4 ± 10.6 MPa for the formulation with the highest (40.7) PAA / PEU w / w%. These values are of the same order of magnitude as human articular cartilage, 8.1 - 15.3 MPa (Parsons, J.R. (1998) ‘Cartilage’, in Handbook of Biomaterial Properties. Boston, MA: Springer US, pp. 40–47. doi:10.1007 / 978-1-4615-5801-9_4), indicating that the sulfonated formulations have comparable physiological hardness.

[0227] Similar to the tangent tensile modulus, the tangent compressive modulus indicates the behavior of the material beyond the elastic region and the rate at which the material undergoes plastic deformation. For the test article with the lowest (17.6%) PAA / PEU w / w%, the tangent compressive modulus was 177.8 ± 8.7 MPa, and for the formulation with the highest (40.7%) PAA / PEU w / w%, the tangent compressive modulus decreased to 145.7 ± 19.5 MPa. The tangent compressive modulus of the non-sulfonated gradient PEU-PAA was 155.9 ± 4.3, corresponding to the sulfonated materials with lower PAA / PEU w / w% or higher PEU content.

[0228] The tear strength follows a trend similar to the tensile and compressive properties and decreases with increasing PAA / PEU w / w% (Table 7). The tear strength values obtained for the range of synthesized sulfonated gradient PEU-PAA were in the range of 28.8 ± 2.2 N / mm to 70 ± 3.8 N / mm, respectively. The tear strength of the non-sulfonated gradient PEU-PAA was 57.7 ± 2.5 N / mm, similar to the sulfonated materials with lower PAA / PEU w / w% or higher PEU content.

[0229] Table 7: Tear strength characteristics of sulfonated gradient PEU-PAA formulations and non-sulfonated gradient PEU-PAA As part of the synthesis, all formulations including non-sulfonated gradient PEU-PAA were equilibrated in SBF prior to packaging and gamma irradiation. Coefficient of friction (COF) values are listed in Table 8. All sulfonated gradient PEU-PAA were observed to exhibit similar friction values (0.034 ± 0.007), significantly lower than non-sulfonated gradient PEU-PAA (p<0.01), regardless of their PAA / PEU content and sulfur content.

[0230] Preliminary assessment of the sulfonation profile across the material thickness indicated that sulfonation was higher on the support side than in the bulk and decreased gradually with increasing depth, as Figure 4 shown (sulfonated gradient PEU-PAA formulation with 48.1 wt% PEU, 14.4 wt% PAA, 37.4 wt% water). The degree of sulfonation was determined by measuring the normalized intensity of the sulfonate peak at 1045 cm -1 relative to the carbonyl peak at 1640 cm -1 using Raman spectroscopy.

[0231] Since the sulfonation reaction conditions were the same for all sulfonated materials, all sulfonated gradient PEU-PAA formulations were expected to have the highest concentration of sulfonate moieties on the support surface, regardless of their PAA / PEU percentage. In contrast, non-sulfonated gradient PEU-PAA equilibrated in SBF exhibited a coefficient of friction higher than 0.1. This indicates that the sulfonation process renders the material lubricious and with low coefficient of friction.

[0232] Table 8: Coefficient of friction of sulfonated gradient PEU-PAA formulations and non-sulfonated gradient PEU-PAA The coefficient of friction of a group of sulfonated gradient PEU-PAA with similar PAA / PEU w / w% (22.9%) and sulfur content (1.05%) was also evaluated. The coefficient of friction of this formulation was 0.042 ± 0.001 (n = 3).

[0233] Therefore, the effect of PAA / PEU percentages in the range of 17.6% - 40.7% and sulfonation conversion of 9% - 31% on mechanical and frictional properties was evaluated. Formulations were compared to non-sulfonated gradient PEU-PAA formulations (40.7% PAA / PEU and no sulfonation) to assess the effect of sulfonation on properties. All IPNs met or exceeded current preliminary specifications. Formulations with lower PAA / PEU w / w% were stiffer than those with higher PAA / PEU w / w%, and this effect was attributed to the increased water content after sulfonation.

[0234] Compared to the non-sulfonated gradient PEU-PAA(0.1), all sulfonated formulations had lower coefficient of friction (COF) in SBF (<0.045), indicating that lubricity of the surface was independent of % sulfonation in the 9 - 31% range studied. All sulfonated formulations showed similar COF values, suggesting that sulfonation percentage or PAA content in the range studied was sufficient to produce a highly lubricated surface in the presence of SBF.

[0235] To further test the ability of the sulfonated formulation of Example 3 to withstand divalent ion effects under physiological conditions, a test was developed to quantify water loss over a wide physiological range of total divalent ion concentration. This test was reported in Ising, H., Bertschat, F., Gunther, T., Jeremias, E., Jeremias, A., & Ising, H. (1995), “Measurement of Free Magnesium in Blood, Serum and Plasma with an Ion-Sensitive Electrode,” Clinical Chemistry and Laboratory Medicine, 33(6), 365 - 372 and Fijorek, K., M., Tomaszewska, D., Tomaszewski, R., Glinka, A., & Polak, S. (2014), “Serum potassium, sodium and calcium levels in healthy individuals - literature review and data analysis,” Folia Medica Cracoviensia, 54(1), 53 - 70 and was used to determine the sensitivity of materials in the low and high physiological ranges by monitoring the percentage of water lost per mM of divalent ion. Sulfonated gradient PEU-PAA and non-sulfonated gradient PEU-PAA test articles equilibrated in SBF (1.8 mM total divalent cations) were placed into buffers ranging from 1.4 mM (low physiological) - 2.2 mM (high physiological) total divalent ion range and their water loss was measured after equilibration. For each concentration, a line was fit and the slope of each line was calculated (Table 9). The divalent ion sensitivity (slope of the fit line) of a representative set of test formulations was plotted ( Figures 3A - 3E ). The sensitivity ranged from -1.32% / mM (percentage of water lost per millimole of total divalent cation) for a formulation with 17.6% PAA / PEU w / w% to as low as -1.86% / mM for a formulation with 40.7% PAA / PEU w / w%.

[0236] Table 9: Percentage of water loss per mM total divalent ions for sulfonated gradient PEU-PAA and non-sulfonated gradient PEU-PAA (n = 5). *The P-value refers to the null hypothesis that the slope is not related to zero (water loss % / mM ≠ 0) A desirable property of synthetic cartilage implants is the ability of the material to retain its water content under physiological conditions. Devices packaged in phosphate buffered saline, once implanted in the human body, are exposed to an environment rich in divalent ions in synovial fluid (∼1.2 mM Ca +2 , 0.6 mM Mg +2 ). The sodium salts of polymeric weak acids (such as PAA) are known to have high selectivity for Ca +2 and Mg +2 , ultimately leading to the displacement of sodium ions (Dorfner, K. (1991) “Ion exchangers,” Berlin, New York: DEGRUYTER. doi: 10.1515 / 9783110862430). Since one molecule of Ca +2 and Mg +2 can bind two carboxylate groups, the PAA chains can become cross-linked through ionic interactions. This can cause the PAA network to contract, resulting in water loss in the body.

[0237] In this example, all sulfonated gradient PEU-PAA formulations exposed to SBF showed less water loss than non-sulfonated gradient PEU-PAA after equilibration. Additionally, within the range of PAA / PEU percentages having mechanical properties equivalent to non-sulfonated gradient PEU-PAA, water loss was further minimized. Specifically, sulfonated formulations with PAA / PEU w / w% in the range of 25.5 - 30% and / or sulfonation levels between 21 - 31% showed less water loss (6.5 ± 0.6 to 9.2 ± 0.5%) than non-sulfonated gradient PEU-PAA (13.8 ± 1.0), and there was no measurable change in weight loss within the range of physiological ion changes tested.

Claims

1. A water - swellable interpenetrating polymer network (IPN) or semi - interpenetrating polymer network (semi - IPN) that forms a molded article, comprising a first polymer network and a second polymer network, wherein the first polymer network comprises a hydrophobic thermosetting or thermoplastic polymer, and the second polymer network comprises a cross - linked ionomer. The cross - linked ionomer has a certain thickness within the IPN or semi - IPN and comprises sulfonic acid - derived carboxylic acid groups, wherein the sulfonic acid - derived carboxylic acid groups are present on the surface of the cross - linked ionomer and extend from the surface into the body of the cross - linked ionomer for a distance of at least 400 microns and at most the thickness of the cross - linked ionomer. Wherein (i) the IPN or semi - IPN comprises a concentration gradient of sulfonic acid - derived carboxylic acid groups, wherein the concentration of sulfonic acid - derived carboxylic acid groups within the ionomer decreases with an increase in the distance from the surface; (ii) the IPN or semi - IPN comprises 15% to 40% (w / w) of the cross - linked ionomer; and (iii) when exposed to water, the IPN or semi - IPN absorbs water to form a water - swollen IPN or semi - IPN with a lubricated surface.

2. The water - swellable IPN or semi - IPN according to claim 1, wherein the sulfonic acid - derived carboxylic acid groups are amino - sulfonic - acid - derived carboxylic acid groups.

3. The water-swellable IPN or semi-IPN according to claim 2, wherein the crosslinked ionomer comprises a measurable amount of the sulfamic acid compound of the formula (H2N) x R(SO3H) y or a salt thereof, wherein R is an organic moiety, x is a positive integer, and y is a positive integer.

4. The water - swellable IPN or semi - IPN according to claim 3, wherein R is a hydrocarbon moiety.

5. The water - swellable IPN or semi - IPN according to any one of claims 2 - 4, wherein the cross - linked ionomer comprises a measurable amount of an amino - sulfonic acid compound selected from taurine and taurine derivatives.

6. The water - swellable IPN or semi - IPN according to any one of claims 1 - 5, wherein the hydrophobic thermosetting or thermoplastic polymer is polyurethane.

7. An orthopedic implant comprising the water - swellable IPN or semi - IPN according to any one of claims 1 - 6.

8. A packaged article comprising the orthopedic implant according to claim 7 contained within a sterile package.

9. The orthopedic implant according to claim 7 or the packaged article according to claim 8, wherein the orthopedic implant is configured to repair or replace cartilage in a joint within the body.

10. The orthopedic implant or packaged article according to claim 9, wherein the joint within the body is selected from the knee joint, condyle, patella, tibial plateau, ankle joint, elbow joint, shoulder joint, finger joint, thumb joint, glenoid fossa, hip joint, intervertebral disc, facet joint, superior labrum, meniscus, metacarpophalangeal joint, metatarsophalangeal joint, phalangeal joint, temporomandibular joint, and wrist joint, or a part thereof.

11. The water - swellable IPN or semi - IPN according to claim 4, wherein the hydrocarbon moiety is an alkane moiety, an alkene moiety, an alkyne moiety, an aromatic moiety, or a hydrocarbon moiety having a combination of two or more of alkane, alkene, alkyne, and aromatic substituents.

12. The water - swellable IPN or semi - IPN according to claim 11, wherein the amino - sulfonic acid is taurine or a derivative thereof.

13. The water-swellable IPN or semi-IPN according to claim 1, having a tensile modulus of from 24.6 ± 0.5 MPa to 48.1 ± 2.8 MPa.

14. The water-swellable IPN or semi-IPN according to claim 1, wherein the molar ratio of sulfonic acid-derived carboxylic acid groups to underivatized carboxylic acid groups varies by at least + / - 50% between two sites in the implant.

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