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Prosthetic 'smart' skin can feel all of the things

A stretchy synthetic skin is embedded with sensors to replicate a skin-like sense of touch for prosthetics.

No, we're not quite at Bishop levels of realism -- at least in terms of looks -- but a "smart" skin developed by researchers at the Seoul National University, Republic of Korea, looks like a hot contender for bringing the sense of touch to prosthetics.

Previous efforts in this regard have consisted of sensors embedded in the prosthetic's fingers, primarily focused on pressure. This is to avoid crushing delicate objects; when you're not sure how much pressure you are applying, it's too easy to apply too much.

Under the leadership of biomedical engineer Dae-Hyeong Kim, the team has developed a skin that can stretch over the entire prosthesis; and its applications aren't just limited to pressure. It's embedded with ultrathin, single crystalline silicone nanoribbon, which enables an array of sensors.

These include pressure arrays, of course, but also temperature arrays and associated humidity sensors, strain sensors, electroresistive heaters and stretchable multi-electrode arrays for nerve stimulation.

"This collection of stretchable sensors and actuators facilitate highly localised mechanical and thermal skin-like perception in response to external stimuli, thus providing unique opportunities for emerging classes of prostheses and peripheral nervous system interface technologies," the study's abstract reads.

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skin3.jpg

Kim et al/Nature Communications

This skin, according to the study, allows for faster response times -- but also more closely replicates the abilities of real skin to sense the world. For example, temperature and humidity sensors would allow the user to touch a child's forehead and feel whether it was hot and damp enough to indicate a fever.

The heaters embedded in the skin, on the other hand, don't provide any sensory feedback; rather, their purpose is to make a prosthetic feel more lifelike by giving it a skin-like temperature profile; while the strain sensors allow send feedback about states such as fatigue as the stretchable skin moves the way real skin would move -- carefully researched by motion capturing the a real hand to map the deformation of human skin in response to complex movement. This allowed the team to carefully map the silicon nanoribbon sensors.

The resulting prosthetic is highly sensitive and adaptable, the team found.

"The prosthetic hand and laminated electronic skin could encounter many complex operations such as hand shaking, keyboard tapping, ball grasping, holding a cup of hot/cold drink, touching dry/wet surfaces and human to human contact," the study read.

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skin2.jpg

Kim et al/Nature Communications

Layering the sensors in a thin film also enhances durability, and reduces the risk of mechanical fractures; while platinum nanowires and ceria nanoparticles allow the electrodes of the prosthetic to interface with the user's peripheral nerves while minimising inflammation.

"As a result, sensing and actuation capabilities are enabled over a wide range of sensory inputs, in the presence of skin deformations, thus providing enhanced function and high performance in the emerging field of smart prosthetics," the study concluded.

The full study can be found online, published in the journal Nature Communications.

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skin4.jpg

Kim et al/Nature Communications