The effects of thermal oxidization of thermal oxidation ofNi-50Ti-23Nb shape memory alloys on biocompatibility

NiTi and NiTi-based shape memory alloys which exhibit shape memory effect (SME) at body temperature find their applications in biomedical studies. In this study, it is aimed to produce NiTi based Ni-50Ti-23Nb alloys which has certain chemical ratio and electron concentration and transforms at body temperature, and then examine their various physical and biocompatibility properties. According to the literature, it is known that in the case of Ni-50Ti-23Nb alloy exhibits austenite transformation at body temperature, so that it is produced in Arc melter furnace. After the production of these alloys, the oxidation was performed and transformation temperatures of the alloys was determined by Differential Scanning Calorimetry (DSC). Oxidized alloys exhibited martensite transformation at body temperature. Then, microstructure and crystal structure of the alloys were examined by SEM-EDX (Scanning electron microscopy) and XRD (x-ray diffraction). The purpose of applying oxidation procedure to Ni-50Ti-23Nb alloy at various temperatures is to improve its biocompatibility. The biocompatibility of oxidized Ni-50Ti-23Nb alloys was investigated by ICP-MS test and cytotoxicity test. For the procedure of ICP-MS test, firstly SBF (Simulated Body Fluid) was produced. The Ni-50Ti-23Nb alloy which was oxidized at 700˚C, was kept in SBF for one and two weeks at body temperature (37 ˚C) and Nickel and Titanium concentrations permeating SBF were measured by ICP-MS. According to the experimental results, it is determined that the amount of nickel element penetrating SBF of the oxidized alloy is very low. Cytotoxicity test was applied to Ni-50Ti-23Nb alloy which was oxidized at 600˚C and it is found that there is no significant cytotoxicity for the sample.