Foam prosthesis for spinal disc

Abstract

Disclosed herein are spinal disc implants comprising a foam adapted to completely or partially replace a nucleus pulposus within a spinal disc cavity, the foam being a nonabsorbable, closed cell and having a Poisson ratio of less than 0.5. Also disclosed are methods of implanting a foam, either as an in-situ curable material or as a preformed foam.

1 . A spinal disc implant comprising a foam adapted to completely or partially replace a nucleus pulposus within a disc nucleus space, the foam being a nonabsorbable, closed cell and having a Poisson ratio of less than 0.5. 
     
     
         2 . The implant of  claim 1 , wherein the foam comprises 30 to 50% by volume of closed cell bubbles. 
     
     
         3 . The implant of  claim 2 , wherein the closed cell bubbles contain less than 50% of a liquid within 1 week or less after implantation. 
     
     
         4 . The implant of any preceding claim, wherein the foam further comprises a radio-opaque marker. 
     
     
         5 . The implant of  claim 4  wherein the marker is selected from tantalum and barium sulfate. 
     
     
         6 . The implant of any preceding claim, wherein the foam adheres to at least one of the annulus fibrosus, walls, and endplates of the spinal disc cavity. 
     
     
         7 . The implant of  claim 6 , wherein the foam adherence takes the form of a covalent bond. 
     
     
         8 . The implant of  claim 7 , wherein the bond strength ranges from 4 lbs/in 2  to 24 lb/in 2 . 
     
     
         9 . The implant of any preceding claim, wherein the foam has a modulus ranging from 0.5 to 10 MPa. 
     
     
         10 . The implant of any preceding claim, wherein the foam has a modulus ranging from 0.5 to 5 MPa. 
     
     
         11 . The implant of any preceding claim, wherein the foam comprises a polyurethane. 
     
     
         12 . The implant of any preceding claim, wherein the foam is sufficiently hydrophilic to wet tissue surfaces. 
     
     
         13 . The implant of any preceding claim wherein the foam has a bimodular compliance. 
     
     
         14 . The implant of any preceding claim, wherein the foam is prepared from:
 a polyurethane prepolymer comprising a polymeric polyol end-capped with diisocayanate, and   a low molecular weight polyisocyanate.   
     
     
         15 . The implant of  claim 14 , wherein the polymeric polyol comprises polyethylene oxide and polypropylene oxide. 
     
     
         16 . The implant of  claim 15 , wherein the polymeric polyol comprises polyethylene oxide in an amount ranging from 70 to 90% by weight and polypropylene oxide in an amount ranging from 10 to 30% by weight. 
     
     
         17 . The implant of  claim 15 , wherein the polymeric polyol comprises 75% polyethylene oxide and 25% polypropylene oxide. 
     
     
         18 . The implant of any one of  claims 14 - 17 , wherein the polyurethane prepolymer is a trifunctional polyol capped with diisocyanate, the trifunctional polyol being formed by trimerizing polymeric diols with trimethylol propane. 
     
     
         19 . The implant of claim any one of  claims 14 - 18 , the polyurethane prepolymer has a molecular weight ranging from 4500 D to 5500 D. 
     
     
         20 . any one of  claims 14 - 19 , the low molecular weight polyisocyanate has a molecular weight of 1000 D or less. 
     
     
         21 . A method of repairing a defect in a spinal disc space, comprising:
 inserting a nonabsorbable, closed cell foam having a Poisson ratio of less than 0.5 into the defect.   
     
     
         22 . The method of  claim 21 , wherein prior to the inserting, the method further comprises removing some or all of the nucleus pulposus within the spinal disc space, and the inserting results in replacement of the removed nucleus pulposus with the foam. 
     
     
         23 . The method of  claim 22 , wherein the removing further comprises removing portions of the annulus fibrosus in the vicinity of the nucleus pulposus. 
     
     
         24 . A method of repairing a defect in a spinal disc space, comprising:
 inserting a composition in the area of the defect, the composition comprising:
 (a) a prepolymer, and 
 (b) a foaming component; and 
   curing the composition to form a nonabsorbable, closed cell foam having a Poisson ratio of less than 0.5.   
     
     
         25 . The method of  claim 24 , wherein the cured foam expands to fill the spinal disc space. 
     
     
         26 . The method of  claim 24  or  25 , wherein prior to the inserting, the method further comprises removing some or all of the nucleus pulposus within the spinal disc space, and the inserting results in replacement of the removed nucleus pulposus with the foam. 
     
     
         27 . The method of any one of  claims 24 - 26 , wherein the cured foam comprises 30 to 50% by volume of closed cell bubbles. 
     
     
         28 . The method of any one of  claims 24 - 27 , wherein the inserting comprises injecting the composition. 
     
     
         29 . The method of any one of  claims 24 - 28 , wherein the composition has a viscosity ranging from 100 cp to 1000 cp. 
     
     
         30 . The method of any one of  claims 24 - 29 , wherein the curing occurs over a period of time ranging from 2 to 5 minutes. 
     
     
         31 . The method of any one of  claims 24 - 30 , wherein the cured foam does not swell more than 30% by volume. 
     
     
         32 . The method of any one of  claims 24 - 31 , wherein the foaming component comprises an aqueous solution. 
     
     
         33 . The method of  claim 32 , wherein prior to the inserting, the composition is adjusted by mixing the prepolymer with the aqueous solution in a ratio that achieves a desired foam compliance. 
     
     
         34 . The method of  claim 33 , wherein the prepolymer and aqueous solution are mixed in a volumetric ratio of 1:1. 
     
     
         35 . The method of any one of  claims 24 - 34 , wherein the prepolymer comprises free isocyanate groups and free amine groups. 
     
     
         36 . The method of  claim 35 , wherein the composition cures through the interaction of isocyanate groups with amine groups, some of which are also present in the tissue of the implantation site. 
     
     
         37 . The method of any one of  claims 24 - 36 , wherein the cured foam exchanges water with the surrounding tissue. 
     
     
         38 . The method of any one of  claims 24 - 37 , wherein the cured foam is a permanent implant. 
     
     
         39 . The method of any one of  claims 24 - 38 , wherein the inserting further comprises a first and second application of the composition, wherein the second application bonds to the first application of the cured foam. 
     
     
         40 . The method of any one of  claims 24 - 39 , wherein the cured foam can be surgically removed from the implantation site. 
     
     
         41 . The method of any one of  claims 24 - 40 , wherein the cured foam provides clinically significant reinforcement to the annulus fibrosus. 
     
     
         42 . The method of any one of  claims 24 - 41 , wherein the cured foam changes height in response to spinal loads. 
     
     
         43 . The method of any one of  claims 24 - 42 , wherein the cured foam begins with a Poisson ratio less than 0.5, changes height in response to spinal loads, and subsequently attains a Poisson ratio of approximately 0.5. 
     
     
         44 . The method of  claim 43 , wherein the cured foam has a Poisson ratio of less than 0.5 at least within 5 days after implantation. 
     
     
         45 . The method of any one of  claims 24 - 44 , wherein the cured foam translates axial forces originating at the vertebral endplates into radial forces applied to the disc annulus. 
     
     
         46 . The method of any one of  claims 24 - 45 , wherein gas in the foam is replaced with fluids from surrounding tissues within about one month or less. 
     
     
         47 . The method of any one of  claims 24 - 46 , wherein a bond strength between the prosthetic and tissue ranges from 4 lbs/in 2  to 24 lb/in 2 .