Muscling in on the real thing

Polymer chemists from Sheffield University claim they have created a system which mimics the flexing of natural muscle.

Based around a self-assembled long-chain molecule, the system could be used as the ‘engine’ for nanoscale devices designed to ‘swim’ through fluids.

The crucial property for a synthetic muscle is that it must expand and contract in response to some stimulus from its surroundings.

Bulk materials can expand and contract, but the repetitive cycles can lead to cracking, so the researchers, led by Richard Jones, a ‘soft machines’ specialist from the university’s polymer centre, and Jon Howse, focused their efforts on gel systems.

‘The simplest basis for a macro-molecular shape change we knew about was the collapse and expansion of a weak polyacid when the pH was changed,’ said Jones. The polyacid they settled upon was polymethacrylic acid, a fairly simple polymer which contains acid groups at regular intervals.

The team incorporated the acid into a molecule known as a ‘triblock copolymer’, where each end of the polyacid chain was capped with a glassy substance called polymethyl methacrylate, or acrylic.