Plastic Nerves May Assist Damaged Spines

The magazine New Scientist (11 May 2002) reports that plastic nerves may one day help people with spinal injuries. Scientists claim to have taken one step towards the goal of forming part of an artificial nerve with thin plastic films designed to behave like nerve cell membranes.

For those who don’t remember their neurological physiology, the following explanation may help in understanding the role of the potential artificial nerves. In nerve cells, waves of sodium and potassium ions cross the cell membrane in opposite directions in response to electrical signals passing along the membranes. Ion channels that line the membrane act as conduits through which the different ions pass, and this flow of ions changes the electrical potential of fluids on either side of the cell membrane. This lets the impulse travel along the nerve. The goal of the artificial membranes is to make a material capable of mimicking these electrochemical reactions that nerves use to convey signals.

Bashford and colleagues at St George’s Hospital Medical School in Tooting, U.S., have created thin films of plastic containing tiny holes that mimic these channels. The holes are created by bombarding very thin sheets (10ěm) of polyethylene terephthalate (PET) with high velocity gold ions from a particle accelerator. ‘These punch their way through it leaving a trail of “broken bonds” in their wake’ says Bashford. These bonds react with a solution of sodium hydroxide to leave a perfectly cylindrical pore lined with carboxyl groups. The pores act like the lining of ion channels, holding the positively charged ion in place.

When the team tested their membrane in a concentrated potassium solution to see how effective the pores were, they found that ions flooded through as rapidly as in natural channels, even though the pores are a thousand times thicker than the real thing. This was encouraging, not only because the plastic membrane seemed to work like the real thing, but because it also seemed to be using the same mechanism.

Of course, a lot of work is needed before the plastic membranes could be used in an artificial nerve, Bashford says. ‘We’d like to make them more nerve-like by making them selective to different ions’, he explains. For example, it is still unclear why the pores in the polymer allow potassium ions to pass through slightly quicker than sodium ions, he says. This and other more complex questions need to be addressed first.

Source Biophysical Journal 2002;82:2032