Researchers have developed electronic skin that can mimic the same process that moves a finger, toe or limb when pricked or scalded. The technology could lead to the development of a coating for prosthetic limbs that would give wearers a sense of touch or help restore sensation in people whose skin has been damaged.
The “e-skin” was developed in the laboratory of chemical engineer Zhenan Bao at Stanford University in California. His team has long tried to make prosthetic skin that is soft and flexible, but which can also transmit electrical signals to the brain to allow the wearer to “feel” pressure, tension or temperature changes.
The latest book, published on May 18 in Sciencedescribes a thin, flexible sensor that can transmit a signal to a part of the motor cortex in a rat’s brain that causes the animal’s leg to contract when the electronic skin is squeezed or squeezed.
“This current e-skin really has all the attributes we crave,” says Bao. “We’ve been talking about it for a long time.”
In healthy, living skin, mechanical receptors detect information and convert it into electrical impulses that are transmitted to the brain by the nervous system. To replicate this, an electronic skin needs sensors and integrated circuits, which are usually made of rigid semiconductors. Flexible electronic systems are already available, but they generally only operate at high voltages that would be dangerous for portable devices.
To create an entirely soft electronic skin, Bao’s team developed a flexible polymer to use as a dielectric – a thin layer in a semiconductor device that determines the signal strength and voltage needed to operate the device. The researchers then used the dielectric to create stretchy and flexible arrays of transistors, combined into a thin, skin-soft sensor.
“We transformed all the rigid materials into soft materials while maintaining high electrical performance,” explains Bao.
The sensor can transform physical changes, such as applied pressure or temperature change, into an electrical impulse. The team also created a device capable of transmitting electrical signals from nerves to muscles, mimicking nervous system connections called synapses.
Bao’s group tested the system on a rat. The skin was wired to the rat’s somatosensory cortex, the part of the brain responsible for processing physical sensations. When the electronic skin was triggered by touch, it sent an electrical signal to the brain, which was then transmitted through the artificial synapse to the sciatic nerve in the animal’s leg, causing the limb to contract.
This type of electronic skin could be used in people who have suffered serious injuries or who have sensory disturbances. Bao says that in the long term, they hope to develop a less invasive system. “We envision that for people who have lost their limbs, we don’t have to implant in the brain,” she says. “We could have an implant in the peripheral nervous system.”
At present, the e-skin has yet to be hardwired to an external power source, but Bao hopes to eventually develop a wireless device. However, to have skin that covers all of the fingers of the hand and that responds to touch, temperature and pressure will require a lot more development, she says.
Still, having a closed-loop system running from sensation to muscle movement is “very exciting”, says Alejandro Carnicer-Lombarte, a bioelectronics researcher at the University of Cambridge, UK. The device made by Bao’s team is “really a proof of concept”, he says, but in the field of artificial prostheses, many groups are working on individual components – thus bringing them all together in one system, like Bao’s team did, is an important step forward. “To combine these things in order is not trivial, I am very impressed by it”, he says.
Carnicer-Lombarte also sees potential for integrating other known technologies into the system, to create, for example, a skin that allows the thumb and little finger to feel different things. He adds that achieving greater sensitivity, so that specific regions of the brain can be targeted, will add to the usefulness of this technology in the future.
This article is reproduced with permission and has been first post May 18, 2023.