SURFACE TREATMENT OF SHAPE MEMORY ALLOY APPLING TO SURGERY MATERIALS AND ITS EVALUATION

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The authors aim to apply Ni-Ti shape memory alloy as an implant material. However, it undergoes pitting corrosion. Thus, the surface of Ni-Ti alloy was coated with Ti by plasma spray, but as a result, the porous ti layr accelerates pitting corrosion of the substrate. The pores of the sprayd Ti layr was made attempt to be sealed with biocompatible polymer resins. In a series of this research, three polymer resins of self-solidified type silicone resin, two-liquid type epoxy resin and instantly-solidified type cyanoacryl resin were employed as a sealant. Their effect on sealing of pores and protection of pitting corrosion was evaluated and discussed. Both the commercial silicone resin adhesive and epoxy resin adhesive employed were so highly viscous that cannot penetrate into porous Ti layr as they are. Dilution of the adhesives by solvents were required. Carbon tetrachloride was the best solvent for silicone resin but acetone was the best for epoxy resin. Moreover, Supersonic wave gave a good effect on penetration of diluted resin adhesives. This seems to be because the air in the pores is easily removed. Cyanoacryl resin adheseiv is so less viscous that it can be considered that it does not need dilution. However, even if cyanoacrylate easily penetrates, it soon solidifies before reaching the bottom of the Ti layr. Therefore, dilution is required to control solidification. From the results of evaluation by electrochemicla polarization experiment, an optimum condition was obtained to reach the bottom of Ti layr for each resins but comparing each other protection abbility to pitting corrosion was ranked as epoxy resin>cyanoacryl resin>silicone resin. Difference in the protection ability seems to be stemed from that in absorbability of water molecules. As another technique for coating trhe alloy, plasma-plating of tetrafluoroethane resin was tried but it could not stand practical usage.