Hydrogel arthroplasty device

Abstract

An arthroplasty device is provided having an interpenetrating polymer network (IPN) hydrogel that is strain-hardened by swelling and adapted to be held in place in a joint by conforming to a bone geometry. The strain-hardened IPN hydrogel is based on two different networks: (1) a non-silicone network of preformed hydrophilic non-ionic telechelic macromonomers chemically cross-linked by polymerization of its end-groups, and (2) a non-silicone network of ionizable monomers. The second network was polymerized and chemically cross-linked in the presence of the first network and has formed physical cross-links with the first network. Within the IPN, the degree of chemical cross-linking in the second network is less than in the first network. An aqueous salt solution (neutral pH) is used to ionize and swell the second network. The swelling of the second network is constrained by the first network resulting in an increase in effective physical cross-links within the IPN.

1 . An arthroplasty device, comprising: an interpenetrating polymer network hydrogel that is strain-hardened by swelling and is adapted to be held in place in a mammalian joint by conforming to a naturally or artificially prepared geometry of a bone in said mammalian joint, wherein said strain-hardened interpenetrating polymer network hydrogel is characterized by having:
 (a) a first network, wherein said first network is a non-silicone network of preformed hydrophilic non-ionic telechelic macromonomers chemically cross-linked by polymerization of its end-groups;   (b) a second network, wherein said second network is a non-silicone polymer network of ionizable monomers, wherein said second network has been polymerized and cross-linked in the presence of said first network and has formed physical entanglements with said first network forming an interpenetrating polymer network hydrogel, and wherein the degree of chemical cross-linking in said second network is less than the degree of chemical cross-linking in said first network; and   (c) an aqueous salt solution having a neutral pH, wherein said aqueous salt solution has ionized and swollen said second network in said interpenetrating polymer network hydrogel, wherein said swelling of said second network is constrained by said first network, yielding the strain-hardened interpenetrating polymer network hydrogel with an initial tensile elastic modulus which is larger than the initial tensile elastic modulus of either (i) said first network of hydrophilic non-ionic telechelic macromonomers as in  1 (a) swollen in pure water or in said aqueous salt solution, said second network of ionized monomers as in  1 (b) swollen in pure water or in said aqueous salt solution, or (iii) or said interpenetrating polymer network hydrogel formed by the combination of said first and second network as in  1 (a) and  1 (b) swollen in pure water,   
       wherein said device is characterized by having a bone-interfacing region and a bearing region opposite to said bone-interfacing region, wherein said bone-interfacing region conforms and fixates to said naturally or artificially prepared geometry of said bone in said mammalian joint. 
     
     
         2 . The arthroplasty device as set forth in  claim 1 , wherein said device is implanted on one side of said mammalian joint forming a hydrogel-on-cartilage articulation in said mammalian joint, or further comprising a second mating arthroplasty device implanted on the opposing joint surface from said implanted device forming a hydrogel-on-hydrogel articulation. 
     
     
         3 . The arthroplasty device as set forth in  claim 1 , wherein said bone-interfacing region is capable of binding to calcium-containing and phosphate-containing bone-matrix constituents of said bone. 
     
     
         4 . The arthroplasty device as set forth in  claim 1 , wherein said bone-interfacing region is pre-coated with calcium-containing and phosphate-containing constituents. 
     
     
         5 . The arthroplasty device as set forth in  claim 1 , wherein said bone-interfacing region is characterized by having a porosity or surface roughness on the order of 10 to 1000 microns to accommodate bone formation and therefore mechanical interlocking of said device and bone. 
     
     
         6 . The arthroplasty device as set forth in  claim 1 , further comprising biomolecules chemically or physically bonded to said bone-interfacing region and said bone-interfacing region is characterized by having a porosity or surface roughness on the order of 10 to 1000 microns to accommodate bone formation. 
     
     
         7 . The arthroplasty device as set forth in  claim 1 , wherein said bone-interfacing region is comprised of a polymeric material chemically bonded to said bearing region which is comprised of said strain-hardened interpenetrating polymer network hydrogel. 
     
     
         8 . The arthroplasty device as set forth in  claim 1 , further comprising an adhesive material bonded to said bone-interfacing region and capable of bonding to said bone, and wherein said adhesive material is biodegradable or non-biodegradable. 
     
     
         9 . The arthroplasty device as set forth in  claim 1 , further comprising a calcium-containing inorganic coating that is chemically or physically bonded to said bone-interfacing region, and is characterized by having a porosity or surface roughness on the order of 10 to 1000 microns to accommodate bone formation. 
     
     
         10 . The arthroplasty device as set forth in  claim 1 , wherein said bearing region and said bone-interfacing region have different compositions at either side of said device and are physically or chemically and physically integrated with each other within said device. 
     
     
         11 . The arthroplasty device as set forth in  claim 1 , wherein the thickness profile of said device approximately matches the natural thickness profile of an original cartilage layer. 
     
     
         12 . The arthroplasty device as set forth in  claim 1 , wherein said device is adapted to fit over a primarily convex three-dimensional bone receiving surface. 
     
     
         13 . The arthroplasty device as set forth in  claim 12 , wherein said device is undersized to fit over said primarily convex bone receiving surface to create an elastic contraction fit over said primarily convex three-dimensional bone receiving surface. 
     
     
         14 . The arthroplasty device as set forth in  claim 1 , wherein said device is capable of swelling to a swollen equilibrium volume in a fluid and temperature other than body fluids and body temperature prior to implantation and capable of de-swelling to a smaller equilibrium volume, compared to said swollen equilibrium volume, upon implantation and exposure to body fluids or/and body temperature, whereby at said smaller equilibrium volume, said device contracts against or physically grips said primarily convex three-dimensional bone receiving surface. 
     
     
         15 . The arthroplasty device as set forth in  claim 1 , wherein said device is adapted to fit within a primarily concave three-dimensional bone receiving surface. 
     
     
         16 . The arthroplasty device as set forth in  claim 15 , wherein said device is oversized to fit against said primarily concave three-dimensional bone receiving surface to accommodate an elastic expansion fit against said primarily concave bone receiving surface. 
     
     
         17 . The arthroplasty device as set forth in  claim 1 , wherein said device is capable of at least partially drying or de-swelling to a dried or de-swollen equilibrium volume in a fluid and temperature other than body fluids and body temperature prior to implantation and capable of swelling to a larger equilibrium volume, compared to said dried or de-swollen equilibrium volume, upon implantation and exposure to body fluids and/or body temperature, whereby said larger equilibrium volume expands said device against a primarily concave three-dimensional bone receiving surface. 
     
     
         18 . The arthroplasty device as set forth in  claim 1 , wherein the hydrophilic non-ionic macromonomer in said first network has a molecular weight between about 275 Da to about 20,000 Da. 
     
     
         19 . The arthroplasty device as set forth in  claim 1 , wherein said hydrophilic non-ionic telechelic macromonomer in said first network is a derivative of poly(ethylene glycol). 
     
     
         20 . The arthroplasty device as set forth in  claim 1 , wherein said ionizable monomers are acrylic acid monomers. 
     
     
         21 . The arthroplasty device as set forth in  claim 1 , wherein the molar ratio between said ionizable monomers and said hydrophilic non-ionic telechelic macromonomers is greater than 100:1. 
     
     
         22 . The arthroplasty device as set forth in  claim 1 , wherein said aqueous salt solution having a pH in the range of about 6 to 8. 
     
     
         23 . The arthroplasty device as set forth in  claim 1 , wherein said first network comprises at least about 50%, 75% or 95% by dry weight telechelic macromonomers. 
     
     
         24 . The arthroplasty device as set forth in  claim 1 , wherein said first network comprises hydrophilic monomers grafted onto said first network. 
     
     
         25 . The arthroplasty device as set forth in  claim 1 , wherein said second network further comprises hydrophilic macromonomers grafted onto said second polymer network. 
     
     
         26 . The arthroplasty device as set forth in  claim 1 , wherein said strain-hardened interpenetrating polymer network hydrogel has a tensile strength of at least about 1 MPa. 
     
     
         27 . The arthroplasty device as set forth in  claim 1 , wherein said strain-hardened interpenetrating polymer network hydrogel has an initial elastic tensile modulus of at least about 1 MPa. 
     
     
         28 . The arthroplasty device as set forth in  claim 1 , wherein said strain-hardened interpenetrating polymer network hydrogel has an equilibrium water content of at least 25%, 35% or 50%. 
     
     
         29 . The arthroplasty device as set forth in  claim 1 , wherein the coefficient of friction of said bearing region of said strain-hardened interpenetrating polymer network hydrogel in an aqueous solution is less than 0.2. 
     
     
         30 . The arthroplasty device as set forth in  claim 1 , wherein said strain-hardened interpenetrating polymer network hydrogel is permeable to said aqueous salt solution and said hydrogel has a permeability coefficient ranging from 1e-18 to 1e-12 m 4 /Nsec. 
     
     
         31 . A method of making an arthroplasty device, comprising:
 providing an interpenetrating polymer network hydrogel that is strain-hardened by swelling and is adapted to be held in place in a mammalian joint by conforming to a naturally or artificially prepared geometry of a bone in said mammalian joint, wherein said strain-hardened interpenetrating polymer network hydrogel is characterized by the steps of:
 (a) providing a first network, wherein said first network is a non-silicone network of preformed hydrophilic non-ionic telechelic macromonomers chemically cross-linked by polymerization of its end-groups; 
 (b) providing a second network, wherein said second network is a non-silicone polymer network of ionizable monomers; 
 (c) polymerizing and cross-linking said second network in the presence of said first network, wherein said second network is forming physical entanglements with said first network forming an interpenetrating polymer network hydrogel, and wherein the degree of chemical cross-linking in said second network is less than the degree of chemical cross-linking in said first network; and 
 (d) ionizing and swelling said second network in said interpenetrating polymer network hydrogel with an aqueous salt solution having a neutral pH, wherein said swelling of said second network is constrained by said first network, and wherein said ionizing and swelling yields to a strain-hardened interpenetrating polymer network hydrogel with an initial tensile elastic modulus which is larger than the initial tensile elastic modulus of either (i) said first network of hydrophilic non-ionic telechelic macromonomers as in  31 (a) swollen in pure water or in said aqueous salt solution, said second network of ionized monomers as in  31 (b) swollen in pure water or in said aqueous salt solution, or (iii) or said interpenetrating polymer network hydrogel formed by the combination of said first and second network as in  31 (a) and  31 (b) swollen in pure water; and 
   
       wherein said device is characterized by having a bone-interfacing region and a bearing region opposite to said bone-interfacing region, wherein said bone-interfacing region conforms to said naturally or artificially prepared geometry of said bone in said mammalian joint. 
     
     
         32 . The method as set forth in  claim 31 , further comprising implanting said device on one side of said mammalian joint forming a hydrogel-on-cartilage articulation in said mammalian joint, or further comprising providing a second mating arthroplasty device and implanting said second mating device on the opposing joint surface from said implanted device forming a hydrogel-on-hydrogel articulation. 
     
     
         33 . The method as set forth in  claim 31 , further comprising precoating said bone-interfacing region with calcium-containing and phosphate-containing constituents. 
     
     
         34 . The method as set forth in  claim 31 , further comprising chemically or physically bonding biomolecules to said bone-interfacing region. 
     
     
         35 . The method as set forth in  claim 31 , further comprising bonding an adhesive material to said bone-interfacing region, wherein said adhesive material is capable of bonding to said bone, and wherein said adhesive material is biodegradable or non-biodegradable. 
     
     
         36 . The method as set forth in  claim 31 , further comprising chemically or physically bonding a calcium-containing inorganic coating to said bone-interfacing region. 
     
     
         37 . The method as set forth in  claim 31 , further comprising at least approximately matching the thickness profile of said device to the natural thickness profile of a corresponding cartilage layer. 
     
     
         38 . The method as set forth in  claim 31 , wherein said device is adapted to fit over a primarily convex three-dimensional bone receiving surface. 
     
     
         39 . The method as set forth in  claim 38 , wherein said device is undersized to fit over said primarily convex bone receiving surface to accommodate an elastic contraction fit over said primarily convex three-dimensional bone receiving surface. 
     
     
         40 . The method as set forth in  claim 31 , further comprising swelling said device to a swollen equilibrium volume in a fluid and temperature other than body fluids and body temperature prior to implantation and capable of de-swelling said device to a smaller equilibrium volume, compared to said swollen equilibrium volume, upon implantation and exposure to body fluids at body temperature, whereby at said smaller equilibrium volume, said device contracts against or physically grips said primarily convex three-dimensional bone receiving surface. 
     
     
         41 . The method as set forth in  claim 31 , wherein said device is adapted to fit over a primarily concave three-dimensional bone receiving surface. 
     
     
         42 . The method as set forth in  claim 41 , wherein said device is oversized to fit against said primarily concave three-dimensional bone receiving surface to accommodate an elastic expansion fit against said primarily concave bone receiving surface. 
     
     
         43 . The method as set forth in  claim 31 , further comprising at least partially drying or de-swelling said device to a dried or de-swollen equilibrium volume in a fluid and temperature other than body fluids and body temperature prior to implantation and capable of swelling said device to a larger equilibrium volume, compared to said dried or de-swollen equilibrium volume, upon implantation and exposure to body fluids at body temperature, whereby said larger equilibrium volume expands said device against a primarily concave three-dimensional bone receiving surface. 
     
     
         44 . The method as set forth in  claim 31 , further comprising grafting hydrophilic monomers grafted onto said first network. 
     
     
         45 . The method as set forth in  claim 31 , further comprising grafting hydrophilic macromonomers grafted onto said second polymer network.