A Terminator-style synthetic skin for robots has been created by scientists.
It heals just like the real thing – and even has human-like sense of touch.
The material could help us feel more at ease around AI (artificial intelligence) at home and in the workplace.
It could also help fuel the rise of sexbots – making them ultra-realistic.
Co author Chris Cooper, a PhD candidate, said: ‘We’ve achieved what we believe to be the first demonstration of a multi-layer, thin film sensor that automatically realigns during healing.
‘This is a critical step toward mimicking human skin, which has multiple layers that all re-assemble correctly during the healing process.’
It’s similar to the futuristic e-skin worn by Arnold Schwarzenegger’s cyborg character.
Human skin has incredible qualities. It senses temperature, pressure and texture. It’s able to stretch and spring back, time and again.
It also provides a barrier between the body and bacteria, viruses, toxins, ultraviolet radiation and more.
Layering was key to replicating them, explained the researchers at Stanford University, California.
Co-author Dr Sam Root said: ‘It is soft and stretchable. But if you puncture it, slice it, or cut it each layer will selectively heal with itself to restore the overall function. Just like real skin.’
Skin, too, is formed of layers. It has just evolved immune mechanisms that rebuild the tissue with the original layered structure through a complex process involving molecular recognition and signaling.
Mr Cooper said: ‘With true “skin” the layers should realign naturally and autonomously.’
The US team hope to develop multi-tiered skin with individually functional layers less than a micron thin each.
A stack of ten or more would be no thicker than a sheet of paper.
Dr Root said: ‘One layer might sense pressure, another temperature, and yet another tension.’
They can be engineered to sense thermal, mechanical or electrical changes.
Lead author Professor Zhenan Bao said: ‘We reported the first multi-layer self-healing synthetic electronic skin in 2012 in Nature Nanotechnology.
‘There has been a lot of interest around the world in pursuing multi-layer synthetic skin since then.’
The current study in the journal Science takes it a step further. The layers self-recognise and align with each other – restoring functionality as they heal.
Existing versions must be repaired manually – by humans. Even a slight alteration might prevent recovery.
The backbone of each layer is formed of long molecular chains connected by dynamic hydrogen bonds – similar to those holding the double-helix of DNA strands together.
It enables repeated stretching without tearing – similar to latex
The researchers used silicone and PPG (polypropylene glycol). Both have mechanical and rubber-like properties and biocompatibility.
Tiny particles trigger conductivity. When warmed both polymers soften and flow – then solidify as they cool.
When heated to just 70°C (158°F), the self-alignment and healing happen in about 24 hours. At room temperature, it can take as long as a week.
The two materials were carefully designed to have similar viscous and elastic responses to external stress over an appropriate temperature range.
Mr Cooper said: ‘Skin is slow to heal, too. I cut my finger the other day and it was still healing four or five days later.
‘For us, the most important part is that it heals to recover functions without our input or effort.’
Adding magnetic materials also led the prototype to self-assemble from separate pieces.
Co author Prof Renee Zhao said: ‘Combining with magnetic field-guided navigation and induction heating, we may be able to build reconfigurable soft robots that can change shape and sense their deformation on demand.’
They could transform warfare – with deployment of indestructible killer robots in the battlefield.
Mr Cooper said: ‘Our long-term vision is to create devices that can recover from extreme damage. For example, imagine a device that when torn into pieces and ripped apart, could reconstruct itself autonomously.’
He showed a short video of several pieces of stratified synthetic skin immersed in water. Drawn together magnetically, the pieces inch toward one another, eventually reassembling.
As they heal, their electrical conductivity returns, and an LED attached atop the material glows to prove it.
The next step is to make the layers as thin as possible – and of varying function. The current prototype was engineered to sense pressure. Additional layers engineered to sense changes in temperature or strain could be included.
In terms of future vision, the team imagines, potentially, robots that could be swallowed in pieces and then self-assemble inside the body to perform non-invasive medical treatments.
Other applications include multi-sensory, self-healing electronic skins that form-fit to robots and provide them with a sense of touch.
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