Hydrogel balloon prosthesis for nucleus pulposus

A prosthesis for replacing or supplementing a nucleus pulposus of an intervertebral disk is disclosed, which comprises a pre-formed expandable balloon having flexible walls defining an inner cavity, the flexible walls having a thickness from about 0.02 mm to about 1.00 mm and a filling tube passing through the flexible walls and in communication with the inner cavity so that the prosthesis is fillable, said pre-formed balloon being adapted to be inserted into the intervertebral disk through a cannula, wherein said flexible walls are made from a material comprising a cryogel formed from subjecting an aqueous solution comprising poly(vinyl alcohol) to repeated freeze-thaw cycles, said expandable pre-formed balloon being filled through the filling tube with a biocompatible material selected from the group consisting of a biocompatible liquid, a biocompatible polymer, and a biocompatible hydrogel in an expanded configuration, and the prosthesis having a tensile modulus of about 0.02 MPa to about 0.8 MPa at 30% strain.