The present invention relates to crosslinking of porous materials made of biodegradable polymers. The method comprises: (a) placing a porous biodegradable polymer in a chamber; (b) introducing a supercritical fluid containing a crosslinking agent into the chamber to effect crosslinking of the porous biodegradable polymer; and optionally (c) introducing a pure supercritical into the chamber to wash the crosslinked polymer until the crosslinking agent is substantially removed from the polymer.