Bioengineering Could Improve Prosthetic Hand Use for Wounded Soldiers

Researchers will present their updated findings Wednesday at the 95th annual Clinical Congress of the American College of Surgeons.

The research project, which was funded by the Department of Department of Defense, arose from a need for better prosthetic devices for troops wounded in Afghanistan and Iraq.

“Most of these individuals are typically using a prosthesis design that was developed decades ago,” says Paul S. Cederna, M.D., a plastic and reconstructive surgeon at U-M Health System and associate professor of surgery at the U-M Medical School. “This effort is to make a prosthesis that moves like a normal hand.”

U-M researchers may help overcome some of the shortcomings of existing robotic prosthetics, which have limited motor control, provide no sensory feedback and can be uncomfortable and cumbersome to wear.

“There is a huge need for a better nerve interface to control the upper extremity prostheses,” says Cederna.

When a hand is amputated, the nerve endings in the arm continue to sprout branches, growing a mass of nerve fibers that send flawed signals back to the brain.

The researchers created what they called an “artificial neuromuscular junction” composed of muscle cells and a nano-sized polymer placed on a biological scaffold. Neuromuscular junctions are the body’s own nerve-muscle connections that enable the brain to control muscle movement.

That bioengineered scaffold was placed over the severed nerve endings like a sleeve.

The muscle cells on the scaffold and in the body bonded and the body’s native nerve sprouts fed electrical impulses into the tissue, creating a stable nerve-muscle connection.

In laboratory rats, the bioengineered interface relayed both motor and sensory electrical impulses and created a target for the nerve endings to grow properly.

“The polymer has the ability to pick up signals coming out of the nerve, and the nerve does not grow an abnormal mass of nerve fibers,” explains Cederna.

The animal studies indicate the interface may not only improve fine motor control of prostheses, but can also relay sensory perceptions such as touch and temperature back to the brain.

Laboratory rats with the interface responded to tickling of feet with appropriate motor signals to move the limb, says Cederna.

The Department of Defense and the Army have already provided $4.5 million in grants to support the research. Meanwhile, the research team has submitted a proposal to the Defense Advance Research Project Agency to begin testing the bioengineered interface in humans in three years.

Addtitional U-M authors of the study include William M. Kuzon, Jr., M.D., Ph.D., head of plastic surgery and professor of surgery; David C. Martin, Ph.D., professor of biomedical engineering; Daryl R. Kipke, Ph.D., professor of biomedical engineering; Melanie Urbancheck, Ph.D., research investigator; and Brent M. Egeland, M.D., surgical resident.

Resources:
U-M Department of Surgery Division of Plastic Surgery
http://surgery.med.umich.edu/plastic/
American College of Surgeons 95th Annual Clinical Congress
http://www.facs.org/clincon2009/index.html