More than 20 million Americans suffer from nerve damage that can result in disabilities including the ability to walk.

Stem cells and donor nerves are used today to replace damaged nerves but the treatments only give suffers some of their functionality back.

Researchers at the University of Pittsburgh School of Medicine are trying to change that and have created a nerve guide that returns 80% of fine motor control in the thumbs of four monkeys. The work was published in journal Science Translational Medicine.

RELATED: RESEARCHERS DISCOVER MOLECULAR SWITCH THAT REPAIRS NEUROLOGICAL DAMAGE

Nerve grew back in a year

The team, led by Kacey Marra, Ph.D. professor of plastic surgery at Pitt and core faculty at the McGowan Institute for Regenerative Medicine, developed a biodegradable nerve guide that was filled with growth-promoting protein.

The proteins can regenerate long sections of nerves that were damaged, eliminating the need for a transplant of stem cells or donor's nerve. The nerve guide was tested on the four monkeys, all of who had a 2-inch nerve gap in their forearms.

"We're the first to show a nerve guide without any cells was able to bridge a large, 2-inch gap between the nerve stump and its target muscle," said Marra in a press release announcing the results. "Our guide was comparable to, and in some ways better than, a nerve graft."

Human trials up next

According to the researchers recovery from the guide was similar to the best-case scenario with graft and outperformed the graft when it came to nerve conduction and in replenishing the cell layers around the nerves that support regeneration. It took a year for the nerve to regrow with the guide, noted the researchers.

Marra and her team want to test her nerve guide in humans and is now working with the Food and Drug Administration on the first human clinical trial.

"There are no hollow tubes on the market that are approved by the FDA for nerve gaps greater than an inch. Once you get past that, no off-the-shelf tube has been shown to work," Marra said. "That's what's amazing here."