Surface modification of shape memory alloys with bio-functional polymers for medical application

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1.Super-elasticity of Ti-Ni alloy(1)Composition of Ti-Ni alloy suitable for super-elasticity at body temperature was investigated by tensile test and DSC. It was found that the composition around Ti-50.85Ni (mol%) was suitable for the purpose.(2)It was found that the heat treatment condition effective to improve the mechanical property of Ti-Ni alloy was between 713 and 773 K for about 0.9 ks.(3)Fatigue strength of the alloy castings was evaluated to be similar to those of CP titanium or Ti-6A1-4V alloy castings.2.Design and fabrication of the alloy stentsStent models were fabricated with Ti-Ni alloy tubes by laser micro-cutting method based on the basic design of self-expanding type stent with super-elasticity.3.Coating on Ti-Ni alloy with bio-fuctional polymers(1)Poly (MPC-co-BMA) with a 0.30 MPC mole fraction (PMB 30) was synthesized as a blood compatible MPC polymer alloy for coating.(2)PMB 30 was coated on the surface of Ti-Ni alloy specimens by spin coating. As the result, the PMB 30 coating layer was not uniform at the marginal part, however, the thickness of the layer decreased with increasing immersion period and became stable at 15-20 nm after 72 h immersion in saline solution.4.Surface modification of Ti-Ni alloy(1)Thickness of the surface oxide layer of Ti-Ni alloy increased, and titanium in the layer was oxidized to Ti^<4+> and became more stable by electrolytic treatment.(2)Nickel concentration in the surface oxide layer decreased after electrolytic treatment, especially by the GLW treatment with the electrolyte composed of glycerol, lactic acid, and water. This treatment was effective in improving the corrosion resistance of Ti-Ni alloy.It was concluded that it was possible to develop new and safe medical devices including stents with superior property in mechanical function, blood compatibility, and corrosion resistance.