Electronic Skin Provides Touch, Pain Sensation to Prosthetic Patients

Researchers from Johns Hopkins University have created an electronic skin that fits over prosthetic devices, allowing users to perceive touch.

Typically, prosthetic users aren’t able to experience touch or other similar feelings, but the e-dermis will allow them to experience a range of sensations, including pain. The electronic skin has two layers that mimic the receptors on the human body.

Researchers working with an amputee volunteer administered electric pulses that activated the subject’s nerves and asked him to score the level of discomfort he experienced in his phantom hand. The team limited the pain to what a subject might experience with an accidental cut by a knife.

The research team created a neuromorphic model that allows the e-dermis to encode sensations the same way skin receptors would. They tracked the user’s brain activity via electroencephalography, or EEG, and determined that the subject did, in fact, experience sensations.

The stimulation patterns provided sensory feedback to the volunteer’s brain while he handled smooth and pointed objects with his prosthetic hand. The researchers also created a reflex response that would cause the prosthetic to quickly let go of an object when it felt pain.

Capitalizing on the idea of the phantom limb, which causes amputees to feel as though the missing body part is still present, the e-dermic stimulates the amputee’s nerves in a non-invasive way. Researchers used transcutaneous electrical nerve stimulation, or TENS. It enables the user to experience a spectrum of sensations, from light touch to painful stimuli.

The e-dermis is made of fabric and rubber laced with sensors that replicate nerve endings. It recreates a sense of touch and pain by sensing stimuli and relaying the messages to the peripheral nerves. 

Researchers explained that our fingers don’t experience touch, our brains do. Our sense of pain protects us from damage and allows us to gauge safety.

Human skin employs an intricate network of receptors that send sensations to the brain. The engineering team used the network as a template for its work.

The challenge is that touch is made of numerous components, including vibration, pressure, and temperature, and there are anywhere from 11 to 20 different channels. The receptors on the back of the hand, for example, are different than the receptors in the palm.

In the future, researchers hope to further develop the technology to make the e-dermis more human and to improve astronaut gloves and space suits.

Johns Hopkins has long been a pioneer in the field of prosthetics, most notably its modular prosthetic limb. The device, capable of replicating most of the movements of a human arm, is the world’s most sophisticated upper-extremity prosthesis.

The MPL is capable of human-like strength and dexterity, and high-resolution tactile sensing.

In 2017, the Johns Hopkins team delivered an MPL to Johnny Matheny, the first person ever to live with an advanced mind-controlled robotic arm. Matheny lost his arm to cancer in 2005, and though there are tasks like driving that he cannot do with the arm, Johns Hopkins hopes to push the prosthetic to its limit.

The group, which received more than $120 million from the U.S. Defense Department to pay for development of the cutting-edge MPL, hopes to have others try the device this year.