fumaric acid or a salt thereof , such as a fumaryl halide , which contains unsaturated carbon - carbon double bonds that can be used for in situ crosslinking , is copolymerized with polydiol in the presence of an alkali metal salt . the resulting photocrosslinkable biocompatible and bioresorbable poly biomaterial is useful in the fabrication of injectable an in - situ hardening scaffolds for application in skeletal reconstruction .