Hybrid Tunnel May Guide Severed Nerves to Rejoin

A biologic tunnel made of both hard and soft materials could guide the reconnection of severed nerve endings, helping nerve trauma patients regain feeling and movement.

Researchers at Pennsylvania State University (Penn State; University Park, USA) developed a novel hybrid conduit that consisted of agarose (a soft hydrogel) as an external wall, along with an internal wall made of an electrically-active conducting polymer to serve as a tunnel that guides the regrowth and reconnection of the severed nerve endings. Since the hydrogel is permeable and expands in water and fluids, the expansion would collapse the tunnel and reduce the ability of the nerve endings to regenerate and connect.


To avoid tunnel collapse, the researchers added a conducting polymer, poly(3,4-ethylenedioxythiophene) (PEDOT) to the design to form a wall that can mechanically support and reinforce the hydrogel. PEDOT is a stable material that can conduct electricity to help electrical signals pass through the nerve. To make sure nutrients and oxygen would reach the regenerating nerve endings, the team created a spiral PEDOT design that maintained the structural integrity of the wall, but allowed some nutrients and air to reach the nerve. The study was published in the November 2012 issue of Advanced Healthcare Materials.

“Autografts are currently the gold standard for bridging nerve gaps. This is an operation that takes the nerve from another portion of the body-for instance-from a tendon, and then it is grafted onto the injured nerve,” said lead author Mohammad Reza Abidian, PhD, an assistant professor of biomedical engineering. “However, the operation can be painful and there are often mismatches in size between the severed nerve endings and the new grafted portion of the nerve.”

The researchers also tested the three designs--plain hydrogel, hydrogel with fully-coated PEDOT wall, and hydrogel with a partially coated PEDOT wall--by implanting the device in 10 mm nerve gaps in rats and measuring the muscle mass and strength of muscle contractions at the end of the nerves. These measurements can indicate whether the separated nerve has reconnected. They found that the spiral PEDOT design generated significantly more muscle mass than the other designs, although it did not generate as much muscle mass as an autograft, which was used as the control design in the study.

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