Shape Memory Alloys

Nitinol, an alloy of nickel and titanium, can be bent into almost any shape and snaps back to its original form when heated. This works because the alloy shifts between two crystal structures, martensite and austenite.

Medical stents made from nitinol are squeezed small for insertion into a blood vessel, then expand to their programmed shape at body temperature. Orthodontic wires use the same trick, applying gentle, constant pressure as the wire tries to return to its memory shape.