Surgical Research : Microchips May Hold Key to Repairing Cut Nerves

A marriage of technologies--microsurgery and microelectronics--in which human nerves are threaded through a silicon chip may be the answer to an age-old puzzle: how to restore use to limbs paralyzed by nerve damage.

Scientists at Stanford University who are trying to learn more about the growth of damaged nerve cells think that within the next decade microchips will help change the fate of many condemned to a life with useless limbs.

“If we can get a genuine direct access to the peripheral nervous system, there is no end to what can be accomplished,” said Dr. Morton Grosser, one of a growing number of scientists trying to join animal tissue function and microelectronics.

He envisions a day when people who have undergone surgery for reattachment of severed extremities will regain complete sensation with implantable chips helping to restore function to crushed or severed nerves.

But for now, the work is in the laboratory and test subjects are rats and monkeys.

“This project is in its nascent stages,” Grosser said. “We’ve been working on it for the last 2 1/2 years and estimate that it will be at least five years before we’ll begin testing in humans.”

Grosser and co-researcher Dr. Joseph Rosen, a Stanford surgeon, have managed to coax nerve endings--tiny axons--to grow through computer chips with tiny holes in them. Axons are the part of a nerve cell through which electrical impulses travel away from the cell body.

The chip could be programmed to electronically reroute axons growing through the holes and make them transmit nerve impulses to the non-functioning limb.

Scientists say that once it is implanted, a chip can act as a “switchboard” or microelectronic “axon processor” to trigger sensation in severed nerves, permitting people with reattached limbs to achieve near-normal use.

“When nerves are severed,” said Grosser, “there’s no signal transmission of any kind, and until a few years ago that was the end of the story.”

But the progress of microsurgery over the last decade has made it possible to actually suture the ends of a nerve together. The surgery is performed under a microscope and usually is performed in conjunction with the reattachment of severed fingers, hands, arms or legs.

“There have been a number of sensational, brilliantly achieved cases where people’s whole arms have been put back on after trauma, and that is a sort of miracle.

“But in most cases that will never be more than an ‘assist limb,’ if the person is more than 4 years old,” said Grosser, who noted that in people over 4 there is little adaptation in the injured nerves.

With the implanted chip, however, muscle movement in an affected extremity would be almost as instantaneous as it would have been without damage.

The brain would send a signal through the nerve and when it reached the damaged portion, instead of being blocked, it would be picked up by the chip and transmitted to the other end of the severed nerve.

To put the size of the experiments in perspective, the nerves scientists intend to reconnect through chips are only one millimeter in diameter.