Artificial skin can 'feel' when it is touched

Stanford University engineers have created a skin-like material which can detect pressure, deliver this signal to a living brain cell and could eventually add “a sense of touch to prosthetic limbs”

The ‘skin’ is a two-ply plastic construct: the top layer creates a sensing mechanism and the bottom layer transports electrical signals and translate them into biochemical stimuli compatible with nerve cells.

The team at Stanford, led by Zhenan Bao, used plastics and rubbers as pressure sensors by measuring the natural springiness of their molecular structures.

They then increased this natural pressure sensitivity by indenting a waffle pattern into the thin plastic which further compresses the plastic's molecular springs.

To exploit this pressure-sensing capability electronically the team scattered billions of carbon nanotubes through the waffled plastic.

Increased pressure on the waffled nanotubes pushed them closer together and allowed electricity to flow through the sensor. Decreased pressure made the flow of pulses relax and indicated a light touch while removing all pressure made the pulses cease entirely.

The team then engineered a line of neurons to simulate a portion of the human nervous system.

It translated the electronic pressure signals from the artificial skin into light pulses, which activated the neurons, proving that the artificial skin could generate a sensory output compatible with nerve cells.

Optogenetics, the biological technique which involves the use of light to control cells in living tissue, was only used as an experimental proof of concept, Bao said, and other methods of stimulating nerves are likely to be used in real prosthetic devices.

Bao's team envisions developing different sensors to replicate, for instance, the ability to distinguish corduroy versus silk, or a cold glass of water from a hot cup of coffee.

Bao said: "This is the first time a flexible, skin-like material has been able to detect pressure and also transmit a signal to a component of the nervous system.

"We still have a lot of work to take this from experimental to practical applications but after spending many years in this work I now see a clear path where we can take our artificial skin."