Abstract
Nitinol (NiTi) shape memory alloy exhibits excellent characteristics for use in biomedical engineering. The material has excellent biocompatibility, corrosion resistance, and wear characteristics, which has increased its use in biomedical applications, including stents and guidewires. While NiTi is becoming more common in medical procedures, most of the use has relied on the superelasticity of the wire, rather than its hysteretic qualities. One reason for this is the difficulty in heating NiTi wire in situ, without damaging adjacent tissue. This research explores the use of focused ultrasound to noninvasively heat NiTi wire above its transition temperature. To demonstrate the memory effect, the wire is strained at low temperature, then placed between porcine muscle samples to mimic an in situ biological environment. Using focused ultrasound, the wire is heated until the NiTi actuates and its shape memory is recovered. Embedded thermocouples located close to the wire measure the local temperature. The study found that higher ultrasonic power resulted in (1) faster actuation of the Nitinol, (2) more complete Nitinol actuation, and (3) lower temperatures in the surrounding tissue with less thermal damage.