Hydrogel balloon prosthesis for nucleus pulposus

Abstract

A prosthesis for replacing or supplementing a nucleus pulposus of an intervertebral disk is an expandable container having flexible walls, the container being adapted to be inserted into a central cavity of an intervertebral disk through a narrow cannula, and the flexible walls are made from a biocompatible hydrogel. A preferred hydrogel is a cryogel formed from an aqueous solution of poly(vinyl alcohol) and poly(vinyl pyrrolidone). The prosthesis may be prepared by dip-coating a mandrel with an aqueous solution of a hydrogel-forming polymer or mixture of such polymers, gelling the coated solution by chilling, and subjecting the gelled coating to a series of repeated freeze-thaw treatments. In use, the prosthesis is inserted into a central cavity of an intervertebral disk and filled with biocompatible material, e.g., a biocompatible liquid, a biocompatible polymer, and a biocompatible hydrogel, particularly a thermogelling hydrogel.

1 . A method of forming an expandable cryogel balloon having flexible walls defining an inner cavity, comprising the steps of:
 (i) dip-coating a mandrel with an aqueous solution comprising poly(vinyl alcohol) to form a coated solution,   (ii) chilling the dip-coated mandrel to a temperature sufficient to cause the aqueous solution to form a gel;   (iii) subjecting the coating to at least two cycles of freezing and thawing to form the cryogel balloon; and   (iv) removing the balloon from the mandrel.   
   
   
       2 . The method of  claim 1 , wherein the aqueous solution further comprises poly(vinyl pyrrolidone). 
   
   
       3 . The method of  claim 1 , wherein the chilling step is performed at a temperature of less than −20° C. 
   
   
       4 . The method of  claim 1 , wherein the chilling step is performed by dipping the coated mandrel into liquid nitrogen. 
   
   
       5 . The method of  claim 1 , wherein the flexible walls have a thickness from about 0.02 mm to about 1.00 mm. 
   
   
       6 . The method of  claim 1 , wherein the balloon has a filling tube passing through the flexible walls and in communication with the inner cavity so that the balloon is fillable. 
   
   
       7 . The method of  claim 1 , wherein the balloon has a shape generally conforming to the shape of a natural nucleus pulposus.