[Experimental studies on polyacetal composites for joint prosthesis].

Abstract

UNLABELLED: Composite polymer resin is one of the most promising materials for its excellent bio-functions. The purpose of the present studies is to prove the applicability of polyacetal composites as a biomaterial for joint prostheses from in vivo as well as in vitro experiments. MATERIALS AND METHODS: The polymeric materials tested in the studies were acetal copolymer resin (POM) reinforced with 20% carbon fiber (CR20), POM with 10% fluorine powder (YF 10), POM alone, ultra high molecular weight polyethylene (UHMWPE) and UHMWPE reinforced with 10% carbon fiber (Poly two). Experiment I: Evaluation of biocompatibility in vivo by injecting polymeric powders into the abdominal cavity of mice, and in vitro with a tissue culture method. Experiment II: Friction and wear tests with a slider and a plate under different lubricants, the slider was made of stainless steel or ceramic. Coefficient of friction and specific wear rate were measured, and the wear surface was observed with scanning electron microscope (SEM). Müller type acetabular cups used for the simulation test were made of reinforced POMs, UHMWPE, and Poly two. A walk simulator was made to test the tribological behavior of hip joint prostheses in which the frictional counterpart was made of ceramic. Roughness of the wear surface, and ultimate frictional torque were measured and the surface microstructure was observed with SEM. Experiment III: Application for joint replacement. As a first step, screwshaped test pieces were inserted into the proximal end of the tibia of Beagle dogs, and ultimate rotating torque was measured to investigate the degree of fixation of reinforced POMs to the bone. A hip joint prosthesis of self-locking and cementless type was made and implanted in 12 dogs. Nine dogs were sacrificed more than 24 weeks after the implantation and investigated radiographically and histopathologically. RESULTS AND CONCLUSIONS: Reinforced POMs showed similar biocompatibility as other biomaterials for joint prostheses. In the combination with ceramic, the coefficient of CR20 tends to decrease with the increase of load and prolapsed time. SEM findings showed low specific wear. After the simulation test, the surface of CR20 cup became smoother. Poly two showed almost the same frictional torque as CR20, but its reinforced carbon fibers seem to be easily drifted away from the wear surface. The CR20 test pieces showed as firm fixation to the bone as those of stainless steel. The implantation tests were excellent in 2 and good in 3 dogs at the point of fixation of the socket with the bone out of 9 dogs tested.(ABSTRACT TRUNCATED AT 400 WORDS)