Embedded Device Stimulates Nerve Recovery, Then Absorbed by Body

Engineers develop the first bioelectronic medicine—an implantable device that stimulates nerve regeneration with electrical pulses. Once the nerve heals, the device disintegrates and the body absorbs it without toxic side effects.

by Lina Zeldovich
January 02, 2019

A team of engineers and researchers at Northwestern University and Washington University School of Medicine produced the first ever bioelectronic medicine—an implantable device that stimulates nerve regeneration by using electrical pulses. Once the nerve heals, the device disintegrates and the body absorbs it without any toxic side effects.

It’s no secret that mild electrical stimulation has a healing effect on damaged nerves. The electrical current enhances the release of neurotropic agents, the body’s natural healing compounds. Some surgeons often perform electrical stimulation during certain operations. When rejoining or suturing two severed ends of a nerve back together, for example, they would place electrodes onto the healthy parts of the nerve for 30 to 60 minutes—with beneficial effects. Repeating these stimulations would further improve recovery, but once the incision is closed, the procedure is no longer possible.

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To solve this problem, the team of surgeons and material engineers built their implantable electrical stimulator to last a certain time and then fall apart into natural elements that the human body can absorb and use. They encapsulated the electronic parts into super thin silicon sheets that bodily fluids eventually dissolve into silicic acid—a non-toxic compound often included in vitamin pills. The biocompatible electronic components were made from magnesium, a metal important for human health and recommended as part of the daily diet. The team also used molybdenum, another metal that the body uses in small amounts. Instead of a battery, the team used a wireless charging method similar to the one used for cellphones.

"We engineer these devices to disappear and get absorbed by the body without any side effects," said John Rogers, material engineering professor at Northwestern and co-author of the study.

Samuel Sia, professor of biomedical engineering at Columbia University School of Engineering and Applied Science, who was not involved in the study, says the device marks a new milestone in advancing this niche area of electronics.

 “The field of biocompatible and bioresorable implantable devices has been really underexplored, and this paper makes a significant contribution,” he said.

Rogers’s team has been working on biodegradable and resorbable electronics for more than six years. They developed a toolbox of various materials that can be used to build various resorbable electronic implants that perform important functions for a certain time, and then simply dissolve, which negates the need of a second surgery to remove them. The life span of the devices can be controlled by the thickness of the silicon sheets that enclose them.  Thicker sheets would last longer, while thinner one would melt sooner.

The device - paper-thin and no larger than a dime - was wrapped around the damaged sciatic nerves of rats for about two weeks before disintegrating and naturally disappearing in their bodies. The Washington University team gave rats a daily hour of electrical stimulation for one, three or six days and monitored their recovery comparing it to no electrical stimulation. The more stimulation the rats received, the quicker and better they recovered, without side effects from their bioelectronic medicine.

The idea of resorbable electronics came out of Rogers’s work on permanent electronic implants. Building implantable electronics that work well and last long was a challenge. “For very thin flexible devices it’s very hard to do—it requires keeping the fluids isolated from active electronics,” Rogers said. “So we started thinking what can we do with devices that don’t last a long time?”

At the same time, he learned from clinicians about a need for temporary devices that would enhance recovery or healing for a period of time, and then would disappear. The two concepts merged together, yielding a new course of study—resorbable or “transient” devices. “We realized that there was a use for these things,” he said.

The study takes transient electronics one step closer to clinical use.

“Researchers have been discussing biodegradable devices for decades, but aside from some simple implants, there have been few products put into patients,” Sia said. “This paper is still at a proof-of-concept, but clearly takes a sophisticated concept of biodegradable implants to a new level of validation.”

Lina Zeldovich is an independent technology writer. 

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