After forty years of struggle, applications for Ni-Ti shape memory alloys (Nitinol) abruptly took off in the early 1990s. The charge was led by medical applications, but hopefully we are now witnessing similar success in the field of actuation. But such explosive growth after a long stagnant period has left much of the fundamental science behind. While one can hardly say the medical industry is flying blind, there are areas in which a stronger scientific foundation is needed. This is particularly important when one considers the criticality of devices such as prosthetic heart valves and stents, and that Nitinol tends to be used only when no other alloy can survive. Here we will review the fascinating history and science behind the shape memory and superelastic effects in Nitinol, and discuss why the alloy has had such an impact to the medical device community. But we will also highlight areas that still need to be better understood, and introduce some of the significant contributions being made at UCSB.
Tom Duerig received his Ph.D. in Materials Science from Carnegie Mellon University in 1979, then worked as a scientist at Brown-Boveri in Switzerland where he became involved with shape memory alloys. In 1983 he settled into Silicon Valley working for Raychem Corporation, unsuccessfully trying to commercialize the technology. Finally recognizing the fit with medical devices in 1991, he left Raychem and started Nitinol Devices and Components (NDC) where he developed self-expanding stents and other medical devices. In 1997 he sold NDC to Johnson and Johnson and remained a president of J&J until 2008, then purchasing back the company. Tom retired as CEO of NDC in 2013 but remains with the company as Chief Technology Officer. NDC (now named Confluent Medical Technologies) has grown to over 800 employees and expanded its technology base to polymers and textiles. Tom also founded the Shape Memory and Superelastic Technology (SMST) society and has written a novel, “Stan’s Leap.”