Biocompatibility and Corrosion Response of Laser Joined NiTi to Stainless Steel Wires

The biocompatibility of nickel titanium (NiTi) wires joined to stainless steel (SS) wires via laser autogenous brazing has been evaluated. The laser joining process is designed to limit the amount of mixing of the materials, thus preventing the formation of brittle intermetallic phases. This process has the potential for manufacturing implantable medical devices; therefore, the biocompatibility must be determined. Laser joined samples underwent nickel release rate, polarization, hemolysis, and cytotoxicity testing. Competing effects regarding grain refinement and galvanic effects were found to influence the corrosion response. After 15 days of exposure to a simulated body fluid, the total nickel released is less than 2 ug/cm2. Numerical modeling of the corrosion currents along the wires, by making use of polarization data, helped to explain these results. Microbiological testing found a maximum hemolytic index of 1.8, while cytotoxicity tests found a zero toxicity grade. All of these results indicate that the autogenous laser brazing process results in joints with good biocompatibility.