an article of manufacture and method of making and implanting the article made of a polyolefin star or linear copolymer are disclosed in which the polyolefin copolymer is biostable and crack - resistant when implanted in vivo . the polyolefin copolymer is the reaction product of a rubbery component which when homopolymerized produces a polymer having a low level of hardness , and a hardening component which when homopolymerized produces a polymer having a high level of hardness . the polyolefin copolymer is elastomeric , has a hardness intermediate the low and high levels of hardness , and has a backbone in which the majority of polymer linkages along the copolymer chain are alternating quaternary and secondary carbon atoms .