Shape-Memory Materials: Possible Uses in the Orthopedic Field

摘要

The properties of shape-memory materials--capable of regaining an initial preimposed shape and thus of developing a preprogrammed state of stress (tension or compression)--are examined, especially those usable for orthopedic applications. The alloys of the NiTi ('Nitinol') type, with properties typical of the other systems too, are considered. The NiTi alloys of roughly equiatomic composition have transformation temperatures close to body temperature, which makes them of interest for biomedical applications. Recovery of shape can be partial or total, reversible or irreversible, depending on the magnitude of the deformation imposed; reversible recovery depends strictly on the thermomechanical treatment given. The Nitinol alloys are of special applicational interest because of their mechanical properties, particularly their fatigue strength and capacity to maintain a significant and constant level of inversion stress. From the orthopedic surgeon's point of view, the observations so far made of these alloys' chemical and physical stability, atoxicity and freedom from carcinogenic effects, as compared with a Co-Cr commercial alloy, have been encouraging. Applications as hip rods and prostheses, for scoliosis and for mandible fractures are cited. Comprehensive Bibliography given.