Bin Hu and colleagues at the Huazhong University of Science and Technology took inspiration from the Atolla jellyfish – a bioluminescent, deep-sea creature that senses changes in environmental pressure and flashes dramatically when it senses danger.
While current electronic skin technologies for prosthetics and robots can detect the slightest touch or breeze, these sensors only operate effectively in a narrow range are unable to respond effectively to a harmful blow. Hu’s team have solved this problem with an electronic skin that can mimic the full range of biological skin’s sensitivity.
Hu told PE how he came up with the idea. “At first, we just tried to mimic the mechanoreceptors in human skin to sensing innocuous mechanical stimuli,” he said.
“Unintentionally, I poked my palm with a nib, and the pain feeling made me realize we overlooked the importance of pain receptors, and that otherwise no one knows the robot is in pain.”
“Therefore, we wanted to find a simple way to express this feeling to let others see when the robot gets hurt, and the Atolla jellyfish came into our story.”
This ‘jellyfish skin’ therefore has the potential to protect prosthetics and robotics from damage. It can sense soft and injurious pressures with sensitivities of up to 0.66 and 0.044 kPa–1 respectively.
Hu added: “We think this technology can assist prosthetics users to learn how to control the strength and the way they use the prosthetic during the adaption period.
“For robots, the technology allows them to express pain through glowing, like when a human shouts when hurt.”
Building on this idea of a visual warning system in response to a physical threat, the researchers have developed a dual-mode approach combining electric and optical systems to create a ‘skin’ that can detect both slight and high force pressures.
This is consistent with how the system works in human skin, where mechanoreceptors are specialised to detect mmechanical pressure or distortion, and nociceptors respond to pain -damaging or potentially damaging stimuli.
The research claims that its complementary sensing ranges allow it to realise a reliable perception to different levels of pressure. Mechanically robust, its stretchable properties are also likely to increase its appeal for use on the surface of robotics and prosthetics.
The electronic skin uses two embedded layers of stretchy poly-dimethysiloxane (PDMS) film, between silver nanowires.
The layers produce an electrical signal in response to slight pressures, such as those created from a light breeze or contact with a leaf.
The PDMS layer sandwiched between the silver nanowire electrodes is embedded with phosphors. As physical force increases, the layer kicks into action and glows with growing intensity.
The researchers claim this approach allows electronic skin to more closely mimic that of human skin, with its ability to respond to a wide range of pressures.
It could also help reduce the costs of maintenance in robotics and prosthetics by warning when there is risk of physical damage.
In addition, Jamie Barras, a teaching fellow in the Department of Informatics at King’s College London, sees uses for the ‘skin’ in medical teaching. He told PE: “For example, I see applications for this type of electronic skin in teaching palpation [examining the body with one’s hands] using phantoms." Phantoms are substitutes for live humans or cadavers, and could be covered in the material to make it easier to determine the right levels of pressure to apply during examinations.
The research appears in ACS Applied Materials & Interfaces.
Content published by Professional Engineering does not necessarily represent the views of the Institution of Mechanical Engineers.