ARTIFICIAL limbs can help people to pick things up, but can’t match the delicacy of real flesh in giving a reassuring caress. That’s about to change with the development of new materials structured to feel more like real body parts.
Modern prosthetic limbs look real – they have skin, hair, and even feel warm, but they’re disconcertingly stiff to the touch. To find out how to make them realistically soft, John-John Cabibihan and colleagues from the National University of Singapore conducted a series of tests in which volunteers shook hands while wearing sensor arrays over the skin. Cabibihan found that the greatest forces – applied on the front and backs of the palms, and on specific sections of the fingers – deformed flesh to depths of up to 3 millimetres.
To see if they could recreate the effect, the team ran computer simulations of artificial tissues made from silicone or polyurethane – the usual materials for prosthetics.
The best designs, they found, were structured in multiple layers with air pockets, 1 to 2 mm thick, running between the layers. In the simulation, prosthetics of this kind deform about 2 mm under forces such as those generated during a handshake, a similar amount to human flesh. This deformation is about 10 times as great as can be achieved with prosthetics made of solid silicone or polyurethane (arxiv.org/1103.5933).
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“The pockets greatly reduce the material’s resistance to force,” says Cabibihan. He adds that it should now be possible to make more realistic prosthetics with a softer internal structure but a tough outer covering for durability.
