a heat shrinkable polymer material is particularly adapted for implanted biomedical use . a polycrystalline polymer is irradiated to produce crosslinking of its intramolecular structure to thereby impart viscoelasticity . the material is biocompatible and suitable for implanted use , from the standpoints of very low toxicity , ability to retain structural integrity and being non - carcinogenic and , moreover , is heat shrinkable at a temperature compatible with such implanted use .