Effect of Silver Addition on Biocompatibility of NiTi and NiTiCu Shape Memory Alloys

NiTi is one of the most widely used biomaterials in such applications as stent, file, denture, etc. Although ternary addition of Cu to NiTi reduces the transformation hysteresis and enhances mechanical properties of the binary alloy, NiTiCu alloys have not been used for biomedical applications owing to their lower cytotoxicity compared to binary NiTi. Addition of silver has been known to reduce cytotoxicity and enhance anti-bacterial behaviour. In the present work, Ag was added as a ternary addition to NiTi and quaternary addition to NiTiCu. High purity nickel, titanium, silver and copper were melted together in a vacuum induction furnace to yield NiTiAg and NiTiCuAg (Ag = 0.5-1.0 at%; Cu = 2.0-7.0 at%)  alloys. The ingots were homogenized at 900 ºC and quenched into water. The ingots were subsequently hot rolled at 900 ºC to 0.5-1 mm thickness. Cytotoxicity tests were conducted through an MTT assay using cultured L6 myoblast cells for both sets of alloys with binary NiTi as positive control. XRD was used to analyze the phases present, while DSC was used to determine the transformation temperatures. SEM and EDX were used to characterize the microstructure and changes in cell morphology.