Prosthetics redesigned with air pockets pass handshake test

Stiff no more. A new design helps synthetic hands yield like human flesh during a firm grasp.
Written by Janet Fang, Contributor on

As realistic as many artificial hands may look, the currently available prosthetics are still much, much stiffer than human skin.

Engineers introduce a redesign that’s structured to feel more like real flesh, even during a firm handshake.

To find out how to make prosthetics real to the touch, the team, led by John-John Cabibihan of the National University of Singapore, examined various new and old configurations of synthetic hands for their ‘skin compliance behavior.’

  1. They used ‘handshake tests’ – where volunteers shook hands while wearing sensors over their skin (pictured) – to identify areas experiencing high contact forces. These were observed where the full grasping enclosure of the other person’s hand took place: on the palms and specific parts of fingers.
  2. Then they experimented on select areas – little, ring, and middle fingers – using an ‘indenting probe’ to figure out the force-displacement. The parts that felt the greatest forces had skin tissue deformed to depths of more than 2 mm.
  3. Simulations were used to compare those force-displacement results from human hands, prosthetic hands made of traditional silicone or polyurethane, and synthetic finger redesigns.
  • The best designs, they found, were structured in multiple layers with open air pockets, 1 to 2 mm thick, running between the layers.

In the simulation, prosthetics of this new kind deform about 2 mm under forces like those generated during a handshake (a 2 N force) – a similar amount to human flesh.

By adding 2 mm of height with open pockets of air to the synthetic fingers increased the skin compliance of the silicone material to 235% and of the polyurethane material to 436%.

Also, while an indentation of 2 N force on the new synthetic skin achieved a displacement of more than 2 mm, commercially available prosthetic hands can only achieve 0.2 mm.

The study was published in the Journal of Neuroengineering and Rehabilitation.

Image: Cabibihan et al.

This post was originally published on Smartplanet.com

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