Shape memory alloy

 Shape memory alloy

Nitinol (an acronym for Ni, Ti Naval
Ordance Laboratory) is an intriguing metal with
very interesting and specific biomechanical
properties. But it is its possibility to be
programmed to change shapes or dimensions in
response to an increase or decrease of temperature
that has aroused considerable interest.
This shape memory phenomenon is a consequence of
particular reaction when cooled through a range of temperatures.
At high temperature (cubic phase) it consists of equiatomic
intermetallic compound NiTi where the atoms are highly
symmetrically arranged resulting in a very stable metal form. At
low temperature (martensite phase) it has however completely
different features allowing for plastic deformation. Consequently
as of the process’ reversibility, the phase transformation brings
along shape modification of a nitinol object. The temperature and
extent of this modification can be by means of specific alloying,
within certain limits, changed. In this way it is possible to adjust
temperature range to particular clinical body applications.
Nitinol is an alloy of Nickel and Titanium and therefore has also
interesting corrosion properties. Nitinol corrosion resistance
pattern resembles that of pure Titanium or its aluminiumvanadium
alloys, which means that exposed to e.g. saline solution
a thin oxide layer forms around the material. Due to the same fact
its biocompatibility is close to that of titanium and relevant studies
proved its sufficient compatibility with living tissues.
Those and some other mechanical properties make nitinol
one of the most innovative concepts. Numerous clinical
applications (in dentistry, maxillo-facial surgery, orthopaedic)
have been proposed and performed since the introduction of this
metal

.