Development of artificial Osteo-chondral composite material

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We investigated and compared biomechanics of natural and artificial joints. The most important functions of the joints rely on excellent lubrication and uniform distribution of impact loads on the underlying bones. As to the lubrication, we measured dynamic changes of the joint space optically and verified the existence of fluid film lubrication in natural joints. From the aspect of fluid film lubri-cation, ultra high molecular weight polythylene(UHMWPE)is not as good a material as polyvinyl alcohol(PVA-H)and articular cartilage. The momentary stress transmitted though the specimens revealed that sub-chondral cancellous bones played the most important role and the UHMWPE had a highter peak stress and ashorter durations of sustained stress than articular cartilage and PVA-H, suggesting a worse dampingeffect. From the results of finite element method (FEM) analysis, intramedullary stem fixation mightnot avoid stress shielding. In artificial joints in the future, it is desirable to preserve as muchsubchondral cancellous bone as possible and to replace the involved joint surface with materials whose mechanical properties are similar to those of articular cartilage. We examined biocompatibility of this material by implanting them into dog's knee joints and confirmed good biocompatibility. In order to fix the materials firmly to the been, we first infiltrate a PVA solution into the pores of porus alumina and bind these two materials by gelling the PVA. We implated this artificial osteochondral composite material into the patellar groove of a rabbit femur. The histological findings of the undecalcified tissue sections revealed considerable new bone ingrowth into the pores of alumina, just two weeks after the operation. Although some problems still remain to be solved, PVA-Hseems to be a very interesting and promising material which meets the requirements of artificial articular cartilage.