Orthopedic implants having gradient polymer alloys

Abstract

Orthopedic implants having a bone interface member and a water swellable IPN or semi-IPN with a stiffness, hydration, and/or compositional gradient from one side to the other and physically attached to the bone interface member. The invention also includes an orthopedic implant system including an implant that may conform to a bone surface and a joint capsule. The invention also includes orthopedic implants with water swellable IPN or semi-IPNs including a hydrophobic thermoset or thermoplastic polymer first network and an ionic polymer second network, joint capsules, labral components, and bone interface members. The invention also includes a method of inserting an orthopedic implant having a metal portion and a flexible polymer portion into a joint, including inserting the implant in a joint in a first shape and changing the implant from a first shape to a second shape to conform to a shape of a bone.

1 . An orthopedic implant comprising:
 a bone interface member having a bone contact surface; and   a water swellable IPN or semi-IPN member having a bearing surface and an attachment zone, the attachment zone being attached to the bone interface member, the water swellable IPN or semi-IPN member comprising a hydrophobic thermoset or thermoplastic polymer first network and an ionic polymer second network configured to exhibit a compositional gradient between the bearing surface and the attachment zone.   
     
     
         2 . The implant of  claim 1  wherein the compositional gradient forms a stiffness gradient. 
     
     
         3 . The implant of  claim 1  wherein one of the networks forms a hydration gradient from a first portion of the implant to a second portion of the implant. 
     
     
         4 . The implant of  claim 1  wherein the bone interface member comprises metal. 
     
     
         5 . The implant of  claim 4  wherein the metal comprises porous metal. 
     
     
         6 . The implant of  claim 1  wherein the bone interface member comprises a ceramic or a polymer. 
     
     
         7 . The implant of  claim 1  wherein at least a portion of the orthopedic implant is configured to change a shape during implant placement in a joint. 
     
     
         8 . The implant of  claim 1  wherein at least a portion of the implant is configured to transiently bend during implant placement in a joint. 
     
     
         9 . The implant of  claim 1  wherein the first network comprises a polyurethane, the implant further comprising a chemical linkage between the IPN or semi-IPN member and the bone interfacing member. 
     
     
         10 . The implant of  claim 9  wherein the chemical linkage comprises a urethane linkage. 
     
     
         11 . The implant of  claim 1  wherein an attachment of the attachment zone to the bone interface member is created by an adhesive. 
     
     
         12 . The implant of  claim 1  wherein the ionic polymer second network has a fixed charge. 
     
     
         13 . The implant of  claim 11  wherein the ionic polymer comprises carboxylic and/or sulfonic groups. 
     
     
         14 . The implant of  claim 1  wherein a thickness of the IPN or semi-IPN member is less than 5 mm in a thickest region. 
     
     
         15 . The implant of  claim 1  further comprising a synthetic joint capsule. 
     
     
         16 . The implant of  claim 15  wherein the capsule comprises fluid. 
     
     
         17 . The implant of  claim 1  further comprising a labral component. 
     
     
         18 . The implant of  claim 1  wherein the implant has a shape selected from the group consisting of: a cap, a cup, a plug, a mushroom, a patch and a stem. 
     
     
         19 . The implant of  claim 1  wherein the implant is adapted to fit an acromioclavicular joint, an ankle joint, a condyle, an elbow joint, a finger joint, a glenoid, a hip joint, an intervertebral disc, an intervertebral facet joint, a labrum, a meniscus, a metacarpal joint, a metatarsal joint, a patella, a tibial plateau, a toe joint, a temporomandibular joint, or a wrist joint. 
     
     
         20 . An orthopedic implant system comprising:
 a first medical implant comprising a water-swellable IPN or semi-IPN comprising a hydrophobic thermoset or thermoplastic polymer and an ionic polymer, the first medical implant having a bone contact surface configured to conform to a bone surface and a bearing surface adapted to mate with a bearing surface of another implant or a natural joint; and   a joint capsule configured to enclose the bearing surfaces.   
     
     
         21 . The implant system of  claim 20  wherein the joint capsule comprises a fluid. 
     
     
         22 . The implant system of  claim 20  further comprising a second medical implant comprising a water-swellable IPN or semi-IPN comprising a hydrophobic thermoset or thermoplastic polymer and an ionic polymer, the second medical implant having a bone contact surface configured to conform to a bone surface and a bearing surface, wherein the first medical implant is configured for placement in one side of a joint, the second medical implant is configured for placement on a second side of the joint and the bearing surfaces of the first and second medical implants are configured to mate, the joint capsule being configured to enclose the bearing surfaces of the first and second medical implants. 
     
     
         23 . The implant system of  claim 20  further comprising a bone interface member physically attached to the IPN or semi-IPN, wherein the bone interface member comprises the bone contact surface. 
     
     
         24 . The implant system of  claim 23  wherein the bone interface member comprises metal. 
     
     
         25 . A hip joint implant comprising:
 a water-swellable IPN or semi-IPN comprising a hydrophobic thermoset or thermoplastic polymer and an ionic polymer, the implant having a bone contact surface configured to conform to a bone surface and a bearing surface; and   a labral component configured to enclose the bearing surface.   
     
     
         26 . The implant of  claim 25  further comprising a joint capsule comprising fluid and configured to enclose the bearing surface. 
     
     
         27 . A composition of matter comprising a polyurethane-polyacrylic acid IPN or semi IPN comprising:
 about 4% to about 90% (w/w) polyurethane;   about 1% to about 40% (w/w) electrolyte of polyacrylic acid; and   about 3% to 80% water,   when analyzed at pH 7.4, 37° C., in an 0.9% aqueous salt solution.   
     
     
         28 . The composition of  claim 27  wherein a concentration of polyurethane is from about 8% to about 55%. 
     
     
         29 . The composition of  claim 27  wherein a concentration of an electrolyte of polyacrylic acid is from about 9% to about 22%. 
     
     
         30 . The composition of  claim 27  wherein a concentration of water is from about 25% to about 80%. 
     
     
         31 . The composition of  claim 27  wherein a concentration of polyurethane is from about 8% to about 55%, the concentration of an electrolyte of polyacrylic acid is from about 9% to about 22%, and the concentration of water is from about 25% to about 80%. 
     
     
         32 . An orthopedic implant comprising a water-swellable IPN or semi IPN having a bearing surface and an attachment surface and comprising a hydrophobic thermoset or thermoplastic polymer first network and an ionic polymer second network, the bearing surface having:
 a coefficient of friction between 0.001 and 0.1;   an equilibrium compressive elastic modulus between 0.8 and 200 MPa;   a water content between 25% and 80%;   a hydraulic permeability greater than 10 −17  M 4 /N sec; and   a failure tensile strain greater than 10%.   
     
     
         33 . The implant of  claim 32  wherein a failure tensile strain is greater than 50%. 
     
     
         34 . An orthopedic implant comprising:
 a polymer bearing member comprising a bearing surface and an attachment zone; and   a bone interface member attached to the attachment zone of the polymer bearing member and comprising metal and open spaces in the metal, the orthopedic implant being deformable from a first shape to a second shape to conform a bone interface member to a bone surface.   
     
     
         35 . The orthopedic implant of  claim 34  wherein the open spaces comprise pores in the metal. 
     
     
         36 . The orthopedic implant of  claim 34  wherein the open spaces comprise slots in the metal. 
     
     
         37 . The orthopedic implant of  claim 34  wherein the bone interface member comprises a plurality of metal members attached to the attachment surface and separated from each other. 
     
     
         38 . The orthopedic implant of  claim 34  wherein the attachment zone comprises a feature selected from the group consisting of: cone, depression, groove, peg, pillar, pin, and pyramid. 
     
     
         39 . The orthopedic implant of  claim 34  wherein the bone interface member is physically attached to the polymer bearing member. 
     
     
         40 . The orthopedic implant of  claim 34  further comprising a chemical linkage between the polymer bearing member and the bone interfacing member. 
     
     
         41 . The orthopedic implant of  claim 34  wherein an attachment of the attachment zone to the bone interface member is created by an adhesive. 
     
     
         42 . The orthopedic implant of  claim 34  wherein the polymer bearing member comprises a water swellable IPN or semi-IPN. 
     
     
         43 . The orthopedic implant of  claim 34  wherein the water swellable IPN or semi-IPN member comprises a hydrophobic thermoset or thermoplastic polymer first network and an ionic polymer second network. 
     
     
         44 . A method of inserting an orthopedic implant into a joint, the implant comprising a metal portion and a flexible polymer having an attachment zone and a bearing surface, the metal portion attached to the attachment zone, the method comprising:
 inserting the implant in a first shape into the joint; and   changing the implant from the first shape to a second shape to conform to a shape of at least a portion of a bone forming the joint.   
     
     
         45 . The method of  claim 44  further comprising changing the implant from the second shape back to the first shape after the first changing step. 
     
     
         46 . The method of  claim 44  further comprising deforming the implant from an original shape to the first shape prior to the changing step. 
     
     
         47 . The method of  claim 44  wherein the joint is a hip joint and the implant is configured for placement on a femoral head and deforming comprises expanding a portion of the implant to fit over the femoral head.