Polymers That Can Simulate Muscles!
(sometimes referred to as 'artificial muscles', or electroactive polymers...)
In robotics today, small electric motors provide the power for metallic fingers to grip objects and artificial arms to bend. However there is an alternative on the horizon that can provide a torque, on par with our own muscles, for these bending tasks.
This alternative is found in certain polymer gels: a gel is not quite a solid, but not quite a liquid either. It's a polymer chain network filled with fluid
Natural gels are: Jello (!), the vitreous humor of the eye, the lining of the stomach, and our muscles. Some artificial gels (polymer gels) are: polyacrylamide, polyacrylonitrile-polypyrrole (PAN-PPY) and polyvinylalcohol (PVA).
The interesting feature about these gels is that they can undergo large swell or shrink in volume (by the absorption or rejection of the fluid from inside the network) as much as 1000x!!!!
The trigger for this change can be a change in temperature, pH, or application of an electric field (the desirable choice, perhaps someday mimicking the body's electrical nerve response?)
Fortunately, these changes are reversible (or the whole thing would be sort of useless…) by restoring the original conditions.
Some websites of interest are:
http://exosci.com/news/141.html
http://ndeaa.jpl.nasa.gov/nasa-nde/lommas/aa-hp.htm