Injured nerves are known to sometime repair themselves, and in certain situations autografts can be performed to bridge gaps in their signal path. Self repair is limited to short distances, while autografts have a number of side effects and limitations.
A team of researchers from Penn State and University of Michigan have developed a way of building hydrogel tunnels that can guide the natural growth of nerve endings. They were able to show that the technique works well over a 10mm distance in rats with damaged nerves. The team plans to conduct further tests at longer distances to see whether natural nerve growth will to propagate further within the tunnels.
Some details from Penn State:
The researchers used agarose, a hydrogel that is permeable and more likely to be accepted by the body. However, because the hydrogel expands in water and fluids, the expansion would collapse the tunnel and reduce the ability of the nerve endings to regenerate and connect, [Mohammad Reza Abidian, assistant professor of biomedical engineering, Penn State], said. They created a second design by adding 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 researchers 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 also looked at optical images of cross sections of the nerve to assess its relative health.
According to Abidian, the spiral PEDOT design generated significantly more muscle mass than the other designs, although it did not generate as much muscle mass as the autograft, which was used as the control design in the study.
The pictures of the spiral PEDOT design showed that the health of the nerve itself was nearly indistinguishable from a nerve photographed after an autograft operation.
Press release: Hybrid tunnel may help guide severed nerves back to health
Study in Advanced Healthcare Materials: Hybrid Conducting Polymer–Hydrogel Conduits for Axonal Growth and Neural Tissue Engineering