Biocompatibility of materials and development to functionally graded implant for bio-medical application

Functionally graded materials (FGM) were fabricated for bio-medical application, especially for implant application, and the effect of gradient structure was evaluated. The titanium/hydroxyapatite (Ti/HAP) and other FGM implants with the concentration changed gradually in the longitudinal direction of cylindrical shape were fabricated by powder metallurgy to optimize both mechanical properties and biocompatibilities or change bioreactivity in each region. Concentration gradient was formed either by sedimentation in solvent liquid or by packing dry powders into mold, followed by compressing and sintering. Electric furnace heating, high frequency induction heating and spark plasma sintering (SPS) methods were used for sintering. SPS could make the stable Ti/HAP FGM. The Brinell hardness decreased gradually from Ti part to HAP part, which contributes for stress relaxation in the implanted region of bone. Tissue response and osteogenesis in animal implantation tests were evaluated from histological observation by optical microscopy and from elemental mapping by EPMA and XSAM (X-ray scanning analytical microscope). Maturation of bone is more advanced in the HAP rich region. The gradient functions in both mechanical properties and biochemical affinity to osteogenesis contribute to the efficient biocompatibility. These results demonstrated that the tissue reaction occurred gradiently in response to the graded structure of FGM, which implies the possibility to control the tissue response through the gradient function of FGM.