FGM's for Biomedical Applications
Functionally graded materials (FGM) were fabricated for bio-medical applications, (1) implants, (2) dental core and post, (3) guided tissue regeneration (GTR) membranes. (1) FGM implants of Ti/HAP and TiN/HAP with the concentration changing gradually in the longitudinal direction of cylinder were fabricated to optimize both mechanical properties and biocompatibility in each region. Concentration gradient was formed by packing of dry powders into mold. Spark plasma sintering was effective for sintering of non-uniform composition in FGM. Brinel hardness decreased gradually from Ti part to HAP part, which contributes to stress relaxation in the implanted region of bone. In vivo tests showed that osteogenesis and maturation is more advanced in the HAP rich region. (2) FGM dental core and post made of composite resin was fabricated by laser lithography, one of the photo-curing type CAD/CAM systems. The elastic modulus changed gradually from 10.6GPa in core part to 2.9GPa at the apex of post by decreasing the filler content of ceramic powders from 64% to 0% in polymer matrix. Stress analysis using finite element method showed the stress relaxation by further 30 % in FGM, compared with the uniform composite resin. (3) Biodegradable GTR membrane composed of nano HAP/collagen reinforced with PLGA was prepared. The membrane has the three layer structure with the thickness of about 100μm for each where the composition of HAP/collagen is increased from pure PLGA. The graded membrane structure could give the different functions of the high degradation speed and Ca ion release to enhance osteoconductivity for bone remodeling in the high HAP/collagen side and the relatively low degradability to prevent the ingrowth of fibroblasts in the pure PLGA side.
F. Watari et al., "FGM's for Biomedical Applications", Advances in Science and Technology, Vol. 45, pp. 1124-1133, 2006