[Polyurethane or silicone as long-term implant substance--a critical evaluation].

Long-term implants made from thermoplastic elastomers have a long history of clinical use. Among other rubber materials, such as polyolefin rubber, much of the demand for rubber-like biomaterials is met by silicone and polyurethane elastomers. The last two elastomers both have sufficient biocompatibility for long-term applications, but differ in terms of biodegradability. Inadequate resistance to degradation almost always leads to implant function loss, which may even threaten the patient's life. Long-term implantation studies in the rat show different mechanisms of biodegradation for polyurethane and silicone. Polyurethane shown deep fissures in the surface, compared with erosion of silicone surfaces. Mechanical and electrical parameters determined to evaluate degradation, additionally show differences in the extent of damage occurring.