A New Process For Joining Nitinol to Stainless Steels For Medical Devices

Nitinol is widely used as core material in medical devices like guidewires and electrophysiology catheters and other applications due to its superelasticity that provides excellent shape retention and kink resistance to the device. In comparison to Nitinol, guidewires with an austenitic stainless steel (SS) core provide superior pushability and torque transmission. With a demand for improved torque response, higher stiffness as well as kink resistance to deliver devices or therapy in tortuous anatomy, there is need for a bimetal guidewires with a SS proximal section and Nitinol distal section. The weldability of nitinol to ferrous alloys like SS is generally poor due to the formation of brittle Fe-Ti intermetallic phases during re-solidification of weld pool. To circumvent this problem, we have developed a new proprietary solid state process for joining Nitinol to SS. The resulting Nitinol to SS joint strength is approximately 80% of the tensile strength of raw Nitinol wire with excellent bend strength. Additional data on bend strength, stiffness and clinical performance data will be presented.