2022 Southern Medical Research Conference

Stanford Team Makes Electronic Skin That Can Sense Touch

Stanford scientists have developed a soft and stretchable electronic skin that can directly talk to the brain, imitating the sensory feedback of real skin using a strategy that, if improved, could offer hope to millions of people with prosthetic limbs.

"We were inspired by the natural system and wanted to mimic it," said Weichen Wang, whose team published its success in the journal Science. "Maybe we can someday help patients to not only restore motor function, but also restore their sensations."

Much faster, larger and more sophisticated circuitry is needed before so-called "e-skin" holds promise for people.

But, in a milestone, the device showed remarkable success in a lab rat. When researchers pressed the rat's e-skin and sent electronic pulses to its brain, the animal responded by twitching its leg.

Scientists have long dreamed of building prosthetic limbs that not only restore movement but also provide perception – sensing pressure, temperature and vibration, for instance — to help restore a more normal quality of life. Skin damage and amputation cause a massive disruption in the loop of perception and movement, so even simple tasks like feeling or grasping an object are challenging.

"If you pick up a glass of beer and you can't sense that it's not cold, then you won't get the right taste," said Ravinder Dahiya, professor of electrical and computer engineering at Northeastern University in Boston, who is also studying the use of flexible electronics to develop artificial skin.

Electronic skin also could be used to clad robots so they feel sensations in the same way that humans do. This is critical to the safety of industries where robots and humans have physical interactions, such as passing tools on a manufacturing floor.

But the sensation of touch is complicated. Human skin has millions of receptors that sense when they are poked or pressed, squeezed or scalded. They react by sending electrical pulses to the brain, through nerves. The brain responds by sending information back, telling muscles to move.

And biological skin is soft and can stretch, repeatedly, for many decades.

The Stanford team, led by chemical engineering professor Zhenan Bao, has been working on e-skin designs for several years. But an earlier effort used rigid electronics and 30 volts of power, which requires 10 batteries and isn't safe. And it wasn't able to endure continuous stretching without losing its electrical properties.

"The hurdle was not so much finding mechanisms to mimic the remarkable sensory abilities of human touch, but bringing them together using only skin-like materials," said Bao, in a statement.

The new e-skin is innovative because it uses networked layers of stretchable organic transistors that perceive and transmit electrical signals. When sandwiched, the layers are only about 25 to 50 microns thick – as thin as a sheet of paper, similar to skin.

Its networks act as sensors, engineered to sense pressure, temperature, strain, and chemicals. They turn this sensory information into an electrical pulse.

And the e-skin runs on only 5 volts of electricity.

To test the system, the Stanford team implanted it into a live rat. When the rat's e-skin was touched, a pulse was transmitted by a wire to the rat's brain – specifically, an area called the somatosensory cortex, which is responsible for processing physical sensations.

The rat's brain responded by sending an electrical signal down to its leg. This was done using a device that amplifies and transmits signals from the brain to muscles, mimicking connections in the nervous system called synapses.

The rat's leg twitched. Significantly, its movement corresponded to varying levels of pressure, said Wang, an engineering PhD and first author on the new paper. For example, the team could increase the leg's movement by pushing the e-skin harder, which boosted the signal's frequency and the transistor's output.

If tested in humans, the device would not require implantation of a wire to send sensory information to the brain. Rather, the team envisions using wireless communication between e-skin and an electrical stimulator located next to a nerve.

Photo of a soft e-skin attached to a finger. The biointegrated e-skin system consists of a temperature sensor, a pressure sensor, and two sets of RO-ED integrated circuits.. (Photo by Jiancheng Lai, Rui Ning) 

Joe McTernan of the American Orthotic and Prosthetic Association said such research encourages technological advancements that could someday provide real-time biofeedback for people who have lost limbs.

"Although this skin technology is fairly new, there has been significant research and development in recent years that have focused on creating a positive tactile experience for the patient," he said.

The Stanford team's closed-loop system — from sensation to muscle movement — is "very exciting…very much a proof of concept," bioelectronics expert Alejandro Carnicer-Lombarte of University of Cambridge told the journal Nature.

In the field of artificial prosthetics, most researchers tend to work on individual components, he said. "Combining those things, in sequence, is not trivial."

Dahiya applauded the team's success in building flexible electronics and then making them work. "That's where they've done a nice job," he said.

But he said there's still a missing piece of the puzzle: creating memory. Unlike Stanford's e-skin, human skin learns how an object feels, then can anticipate it.

There's another challenge: The transmission of signals is currently too slow to be useful. The flow of information through the team's flexible carbon-based transistors is sluggish compared to more traditional silicon-based transistors, he said.

Such a delay "will not allow us to get a real feeling," Dahiya said. "And without real feeling, then you have a practical bottleneck."

At Stanford, the next step is to pack more and different sensors into the e-skin, to more closely replicate the many sensations felt by the human hand, said Wang.

"We're scaling up," he said. "It will be more advanced.

"The whole field is under development," he said. "It will take many more generations of developments to realize our target."

Stanford Provost Announces Plans To Step Down This Fall

Stanford Provost Persis Drell plans to step down later this year once her successor is in place, the university announced on Wednesday, May 3.

Drell moved into the provost role in February 2017 and has been in charge of leading the university's academic functions and overseeing its budget. She plans to leave the position during the fall quarter but will remain a faculty member and continue to teach at the university, Stanford said in a press release announcing the change.

University President Marc Tessier-Lavigne plans to create a faculty-led advisory committee to oversee the search for Drell's replacement. That committee will be chaired by Debra Satz, the dean of Stanford's School of Humanities and Sciences, the university announced.

"Persis has led vigorously with spirit, candor, good humor, deep thoughtfulness, and steadfast dedication to Stanford's mission of teaching and research," Tessier-Lavigne said in the press release. "She has worked with our faculty to support and continually advance the academic excellence of Stanford, and she has had a major impact on nearly every aspect of university life."

As provost, the deans of Stanford's seven schools report to Drell, along with vice provosts who have roles in areas including research, education, student affairs, budget, faculty development, and equity and access, according to the university.

A physicist by training, Drell has a long history at Stanford. She grew up on the university's campus, with her father, physicist Sidney Drell, working as a Stanford professor.

Persis Drell went on to get her bachelor's degree from Wellesley College and doctorate from the University of California, Berkeley. She ultimately returned to Stanford in 2002 to serve as a professor and director of research at the SLAC National Accelerator Laboratory.

She was later the director of SLAC and then the dean of the School of Engineering. In February 2017, she was named provost, several months after Marc Tessier-Levigne took over as president. Her predecessor, John Etchemendy, left with prior President John Hennessy.

In the press release announcing her decision to step down, Drell said that she was grateful for the opportunity to be provost and praised the university's students, faculty, staff and community.

"This is the right time," Drell said. "I began sharing with Marc some time ago my thoughts about the rough timeframe to complete my role as provost. Making the transition now provides the opportunity for a new provost to be in place in the fall quarter. I look forward to continuing to focus on the work of the Provost's Office until my successor is in place."

In her time as provost, Drell worked with Tessier-Lavigne to create the university's Long-Range Vision, which guides the university's work and direction. When COVID-19 hit, she was in charge of the university's "operational response" to the pandemic, including chairing the policymaking committee, the press release said. She also spearheaded the Inclusion, Diversity, Equity and Access in a Learning Environment (IDEAL) initiative, which is meant to promote a sense of belonging on campus.

Board of Trustees chair Jerry Yang praised her work as provost and said that the board respects her decisions to leave the position.

"Persis has heartfelt thanks and admiration from the board for her energy, her leadership, and her unflagging dedication to preserving and amplifying the academic excellence of Stanford," Yang said in the release.

Role Of Hospitals: Stanford Medicine Children's Health

When Eloise (Ellie) McCloskey turned 11, she got the best birthday present she and her family could have asked for: a phone call from Stanford Medicine Children's Health, telling her a donor heart — which Ellie desperately needed — had been identified for her.

Ellie was diagnosed with dilated cardiomyopathy at the age of 7, and by age 10, a new heart was in order. But thanks to three innovations that shortened Ellie's time on the transplant wait list, as well as an established partnership between Stanford Children's and her local Oregon hospital, Ellie was able to get her new heart fast. Within days of her 11th birthday, she had flown to Palo Alto and undergone a successful surgery.

Stanford Medicine Children's Health used three tactics to speed up Ellie's transplant: 1) Rather than a traditionally healthy heart, they found Ellie a heart infected with hepatitis C, which is fully treatable and therefore becoming increasingly common among cardiac transplants, 2) Through their 3D cardiac imaging center, they were able to analyze the size of Ellie's donor heart and confirm that it was the right size for her body, and 3) They used a technology that increases the window of time that a heart can be outside the body and remain viable for a transplant, informally called Heart in a Box.

Read more about Ellie's transplant experience at Stanford Medicine Children's Hospital on Stanford's Healthier, Happy Lives blog.

Resources on the Role of Hospitals

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