Researchers Regrow Damaged Nerves Without Graft

Julia Robitaille ’23

 A team of medical researchers led by Neil Fadia and Jacqueline Bliley at the University of Pittsburgh recently became the first to bridge a two-inch nerve gap without the help of an existing nerve implant or stem cells. Their revolutionary polymer tube essentially guides a damaged nerve ending to its target muscle, reducing the likelihood of complications and the need for a graft. This polymer tube nerve guide may provide a better outlook for patients than current nerve graft procedures. [1]

Damaged or severed peripheral nerves (nerves outside of the spinal cord and brain) can regrow up to one third of an inch on their own. However, if the damaged portion is longer, the nerve can get disoriented and form a painful bundle called a neuroma. The current standard treatment for repairing a long section of a damaged nerve is to harvest a section of a thin, long nerve (usually in the back of the leg) which is sliced into three segments, twisted into a thick bundle, and attached at the site of the damaged nerve. This nerve graft grows and fuses over a long period of time until the whole nerve is intact and limb function returns. Since this procedure requires a graft from a preexisting nerve, it often results in partial loss of sensation in the area where the existing nerve was harvested. In addition, the procedure only returns an estimated 40% to 60% of motor function in the repaired nerve. Given these statistics, it may be argued that the existing procedure is not worth the sacrifice. [1],[3]

Figure 1: An anatomical illustration of peripheral nerves in the human arm.
Source: Wikimedia Commons, Henry Vandyke Carter [Public domain]

An alternative procedure for long nerve growth would be immensely beneficial, considering an estimated 20 million Americans are affected by nerve damage. Civilians severely damage nerves every year due to trauma-related accidents, complications from cancer treatment, and nerve-damaging diseases, such as diabetes. Wounded veterans often return from combat with permanent nerve damage that impacts them for the rest of their lives. [1]

Fadia and Bliley’s new nerve guide procedure proposes an alternative procedure for nerve regrowth, eliminating the need for a graft and thereby reducing complications involved with nerve harvest. Using the same material as suture thread, researchers create a polymer tube and sprinkle it with slow-releasing growth-promoting proteins. The implanted tube then guides the growing nerve to its destination, reducing the likelihood of neuroma formation. [1]

Researchers compared the results of a classic nerve graft to their polymer-aided nerve guide in the forearms of monkeys. In the standard procedure, a 2-inch section of nerve was harvested from the monkey’s forearm (monkeys’ legs are not long enough to harvest from). Since the nerve was harvested from the same arm in which it was implanted, it was flipped around to make it more realistic to a human procedure, in which a nerve from a completely different limb is harvested. In the nerve-guided procedure, the polymer tube guide was attached to the end of a 2-inch nerve gap in the monkey’s forearm. Both nerves were allowed to grow over a 2-inch gap, and in both procedures, it took about one year for the repaired limb to regain substantial functionality. However, the polymer nerve guide procedure restored Schwann cells better than the normal procedure. Having this protective layer of insulating cells makes signal transmission stronger and faster. [1],[3]

Both the standard nerve graft and the polymer-aided nerve guide restored function in the monkey’s forearm at about the same rate. However, the protein- enhanced nerve guide yielded a smaller loss of nerve conduction compared to the autograft and avoided sacrificing another nerve to do so. The researchers at Pitt hope to eventually use this relatively long 2-inch biodegradable nerve guide to treat patients with large-scale nerve damage, in which independent growth is not feasible. [2]

 

References:

[1] University of (2020, January 22). Researchers regrow damaged nerves with polymer and protein. ScienceDaily. Retrieved from www.sciencedaily.com/releases/2020/01/200122150015.htm

[2] Neil B. Fadia et al. (2020). Long-gap peripheral nerve repair through sustained release of a neurotrophic factor in nonhuman Science Translational Medicine, 12 (527). DOI: 10.1126/scitranslmed.aav7753

[3] Chawla, (2019, November 9). Peripheral Nervous System Anatomy. Medscape. Retrieved from https://emedicine.medscape.com/article/1948687-overview

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