Flexible, wireless skin interface could restore amputees’ sense of touch

VR hardware tends to focus on using a headset to convey visual and auditory information, giving users a realistic experience of virtually generated sights and sounds. But what about another equally important sensation — touch? With the right technology, tactile sensation technology could let people virtually hold hands from across the globe, experience full-body VR immersion, or even restore a sense of touch to those who have lost a limb.

A new paper published today in Nature describes how this is possible through a new type of flexible, wireless interface that can communicate touch information via the skin. The researchers call it “epidermal VR.”

Professor and lead researcher John Rogers of Northwestern University told Digital Trends about how the technology works and how it is already being used by amputees to improve their quality of life.

How epidermal VR works

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Diagram showing the layers of the VR patch which allow the transmission of information as vibrations. The copper-colored layer in the middle represents the wireless power circuits containing the electronic components. Northwestern University

The basis for the system is a flexible wireless patch that is 15 by 15 centimeters in size. Slim and soft like a sheet, the patch can be comfortably worn on various areas of the body as it drapes over curves and does not require wires or a battery.

Embedded within the patch is an array of 32 tiny actuators, each of which can vibrate individually. The patch is linked to a touchscreen interface on a smartphone or tablet, and users can use their fingers to touch the screen in any pattern. This touch is detected by the interface and transmitted to the actuators in the patch, which vibrate in a pattern corresponding to the touch.

Similar ideas have been developed in the past, but they have been limited by bulky battery packs or tethering wires. The Northwestern team used their expertise in wireless power transfer to do away with the wires and drew on their previous work in stretchable electronics to create a patch that was flexible and comfortable to wear.

To transfer a feeling of touch from the interface to the flexible patch, both data and power need to be transmitted. For this purpose, the team used a technology that will be more familiar as part of a smartphone. “We use near-field communication (NFC) protocols, i.e., the same type of technology used in smartphones for wireless payments,” Rogers explained. “This interface supports both real-time digital control and power delivery.”

Restoring a sense of touch

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Retired U.S. Army Sgt. Garrett Anderson shakes the hand of Aadeel Akhtar, one of the researchers who developed the new VR system. The patch on Anderson’s upper arm allows him to feel transmitted sensations from his prosthetic fingertips. Northwestern University

One of the most remarkable applications of the technology is helping amputees to experience a sense of touch from their missing limbs. The system was tested out by retired U.S. Army Sgt. Garrett Anderson, who lost his arm while serving in Iraq.

The researchers put the flexible patch on Anderson’s upper arm, where he could feel the vibrations, and connected it wirelessly to sensors on the fingertips of his prosthetic arm. He could then feel feedback from his prosthetic fingers in his upper arm, with stronger vibrations indicating a firmer grip and gentler vibrations indicating a looser grip.

This system has immediate tangible benefits for people such as Anderson who need sensory information from their prostheses to interact with objects. “Say that I’m grabbing an egg or something fragile,” Anderson said in a statement. “If I can’t adjust my grip, then I might crush the egg. I need to know the amount of grip that I’m applying, so that I don’t hurt something or someone.”

The benefits aren’t just practical though. There’s an enormous psychological benefit in being able to experience the touch of family and loved ones. “My kids are 13 and 10, so I have never felt them with my right arm,” Anderson said. “I don’t know what it’s like when they grab my right hand.”

Making the system work for more people

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Anderson grabs and grips an object while wearing Northwestern’s wireless patch. Northwestern University

The experience isn’t exactly like having your old sense of touch back, Rogers explains, due to differences in how densely packed sensory receptors are in different areas of the body. “The density of sensory receptors in the skin of the upper arm is much lower than that in the fingertips, such that the recreation of the sensation of finger-touch can only be approximate,” he said. “But in most cases, the sensory inputs to the arm can equal the number of sensors on even the most sophisticated prosthetic fingertips.”

It takes some time for users to learn the connection between the sensations from the device — in this case, from the upper arm — and the sensory information being transmitted — in this case, from the fingertips. Eventually, after using the device regularly, the brain begins to recognize sensations in the arm and converts them to an equivalent sensation of touch.

Exactly how long this process of adaptation takes will vary between users, Rogers predicts. “The ability of someone to use the information is very dependent on the individual, and we don’t — at the present time — have data on sufficient numbers of patients to make statements on the time frames,” he said. The group will continue to work on making the system available to more people to see how different individuals respond and adapt to the information.

The technology may even be able to help those who experience phantom pain in their amputated limb, by replacing the phantom sensations with external sensations instead.

Future applications

In the future, the system could be adapted for everything from full-body suits for a totally immersive VR experience to adding a sense of touch to video calls. Rogers says his team has worked to make the system easy for others to scale up for different functions.

“We’ve tried to design the systems — the architecture, the components, the assembly processes, the materials, etc. — to be scalable by retaining alignment with the types of manufacturing capabilities that are used in conventional consumer gadgetry,” Rogers said. This means that companies or other groups can take the concepts the team has developed and adapt them to different commercial or research needs.

For now, the Northwestern group will continue working on improving the actuators in the system and making the device even slimmer and lighter. They are also interested in adapting the system to detect and transmit information about different sensory modalities such as temperature and shear forces. Eventually, the system could be used by people like Anderson to feel not only touch but to detect heat and stretching sensations as well.

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