Smart wire is a shape memory alloy (SMA) that changes its length with a useful pulling force when a small current is passed through it.

SMA is a smart material which, as its name suggests, has a memory. The most common SMA is an alloy (mixture of metals) of nickel and titanium -called nitinol. By means of special heat treatment, a piece of SMA can be made to 'remember' a shape. For example, a length of wire can be made to remember that it should be straight at temperatures above 70°C. If you bend this wire at normal room temperature into the shape of a paper clip, it stays bent and will continue acting as a paper clip. However, if you place it in a glass of water whose temperature is above 70°C, it immediately straightens out! When cool, it remains straight until it is bent again.This cycle of bending and then straightening when heated can be continued millions of times. The temperature at which SMA 'remembers' its original form is called the transition temperature and when this point is reached, it changes shape.

SMA has a relatively high electrical resistance and can be heated to its transition temperature by passing an electrical current through it. 

• Resistance: 150Ω per metre
• Maximum Current: 180 milliamps
• Maximum Power: 5 Watts per metre
• Bias Force: 0.3 N
• Pulling Force: 1.5 N