Peripheral nerves that spread extensively in our arms, legs, and torso can get damaged due to an injury resulting from sports, road accidents, or occupational hazards (e.g. too much typing). Peripheral nerve injury constitutes 2–5% of all trauma cases, wherein the affected individual may experience weakness or numbness in the affected body parts1,2. Fortunately, unlike neurons – the nerve cells in the brain and spinal cord – peripheral nerves can regenerate. The affected individual may require medical attention, in the form of painkillers and physical therapies or, in certain cases, surgical intervention. During a surgical procedure, it is common practice to electrically stimulate the nerves to promote regeneration. However, the surgeon must close the wound within a couple of hours, to avoid chances of infection. Thus, it is not possible to continue the electrical stimulation of nerves after the surgery.

In the last few years, we have witnessed the development of a new class of electronics: miniature bioabsorbable devices. These are made of porous silicon and silk, and can be designed to have a specific lifespan in the body. Originally, researchers from Northwestern University used this silicon-based “complementary metal oxide semiconducter” or CMOS to demonstrate its programmable non-antibiotic based bacteriocidal properties, as proof of principle3. The device, wrapped around the injured nerve, uses electrical pulses for nerve stimulation for a programmed number of days before it harmlessly degrades in the body. This research established a baseline of modeling approaches, starting materials, and designs of the various electronic components involved (sensors, power supplies etc.). In vivo tests established that the rate of disappearance of the device matched the theoretical prediction models.

Expanding on these findings, additional collaborative research from Washington University St. Louis and Northwestern University, recently demonstrated the ability of an implanted, bioabsorbable device, which can aid recovery of injured nerves with electrical stimulation4. The device, made of soft, flexible, dissolvable electronic materials, is kept charged wirelessly using a transmitter outside the body.

The team tested their device in studied rats with severed sciatic nerves, which regulate the flow of nerve impulses in the hamstring and lower leg muscles, in one of the hind legs. The severed nerve endings were stimulated using the implanted programmable device (dimensions: ~ 10 mm x 40 mm x 200 μm; weight: 150 mg) for 1 hour per day for 6 days. The researchers reported a 50% faster rate of nerve healing in the electrically stimulated animals, when compared to their unstimulated counterparts. The constituents of the implanted device were completely bio-reabsorbed in a controlled, time-defined manner, upon exposure to the physiological fluids in the tissue.

This promising research area is growing rapidly. Currently, research groups from the University of Wisconsin-Madison are extending this study for other applications, including rapid healing of skin and weight loss. Researchers at Rice University, Houston are trying to shrink the device further to make them implantable in the brain. Once successful, they hope to replace the large brain stimulators used to control tremors in Parkinson’s patients with these miniature devices.

Of course, the safety of the dissolved device components needs to be monitored for any possible side effects. In the future, bioresorbable electronic implants can power interventions across a wide range of clinical applications, with benefits to a range of targeted tissues and organ systems.

References

  1. Mackinnon SE. Nerve Surgery. New York: Thieme; 2015.
  2. Noble J, Munro CA, Prasad VS, Midha R. Analysis of upper and lower extremity peripheral nerve injuries in a population of patients with multiple injuries. J Trauma. 1998 Jul. 45 (1):116-22
  3. Hwang SW, Tao H, Kim DH, et al. A physically transient form of silicon electronics. Science. 2012;337(6102):1640-4.
  4. Koo, J. et al. Wireless bioresorbable electronic system enables sustained nonpharmacological neuroregenerative therapy. Nat. Med. 24, 1830–1836 (2018)

About the author: Maya Raghunandan obtained her Ph.D. in Biochemistry and Molecular Biology from the University of Minnesota, Twin cities, USA. Currently, she is a cancer biology scientist at Université Catholique de Louvain, Brussels, Belgium. In her spare time, she writes about cool science discoveries in her jargon-free blog http://www.sciencesnippets.org/. Because science doesn’t have to sound complicated. Instead, it must be comprehensible for everyone.