"Where do you get the nerve?"
In the future, the answer to that question may well be "from advanced research conducted in the state of Iowa."
While stem cell research and the hope it promises to thousands of people with nerve damage may be on hold, another process for regrowing damaged nerves may still work for those suffering from peripheral nerve damage.
The process has the advantages of not being controversial and is being developed right in our own back yard.
Using microscale channels cut in an ultrathin biodegradable polymer, Surya Mallapragada, a researcher at the U.S. Department of Energy's Ames Laboratory, is working to regrow nerve cells.
The technique may one day allow the paralyzed to walk and the blind to see and has been proven to work for peripheral nerve regeneration in laboratory rats.
Nerve cells are unlike most other biological tissue. When a nerve is severed, the part of the neuron "downstream" of the injury typically dies.
Neurons in the human body can be several feet long. Grafting works well for skin and other tissue, but is not the best option for nerves because there can be a loss of function where tissue is removed from the donor.
There is also no guarantee that nerve cells will line up and reconnect.
"Nerve cells aren't able to easily bridge gaps of more than one centimeter," said Mallapragada, an Ames Laboratory associate in materials chemistry and a chemical engineering professor at Iowa State University.
"Peripheral nervous system axons - the part of the nerve cell which carries impulses - normally have a connective tissue sheath of myelin guide their growth, and without that guidance, they aren't able grow productively."
In layman's terms, the nervous system carries electrical impulses. Nerve cells are like electrical wiring. Bundles of nerves are like an electrical cable with multiple wires.
When a nerve "cable" is cut and cells die, it would be as though the copper wire downstream of the damage disappeared, leaving only the empty plastic insulation tubes.
In order for new copper wiring to push out across the gap and fill in the empty insulation tubes, you'd need a way to guide the wires into the empty insulation. That is where Mallapragada's research comes in.
By working on a cellular scale, she has developed a way to help guide neurons so they grow in the right direction. Starting with biodegradable polymer films only a few hundred microns thick (100 microns equals 0.004 in. - significantly less than the thickness of a human hair), Mallapragada and her colleagues have developed methods for making minute patterns on these incredibly thin materials.
"We've made grooves three to four microns deep to help channel nerve cell growth," Mallapragada said. "The grooves have a protein coating, and we've also seeded them with Schwann cells to help promote this growth."
Schwann cells naturally form the myelin sheath around the PNS cells. When guided by this sheath, nerves will grow at a rate of three to four millimeters per day.
To put the microscale grooves in the polymers, she used laser and reactive ion etching.
Mallapragada worked with ISU's college of veterinary medicine to conduct trials on rats. Small segments of sciatic nerves that deliver messages to the hind legs were removed from the rats. The severed nerves were spliced using the polymer film.
Though initially unable to use their legs, the rats started to regain use of their legs after three weeks and were able to function normally after six weeks.
According to Mallapragad, the technique has shown great promise, but getting similar results with the central nervous system - the brain, spinal cord and optic nerve - is another matter.
CNS cells grow differently than peripheral nerves, presenting special problems. The connective tissue of the CNS can actually inhibit nerve growth.
Mallapragada is focusing the next phase of her research on the optic nerve to try to better understand how CNS neurons work and grow.
"There are other factors at work, such as chemical and electrical cues," Mallapragada said. "Other researchers have had some success injecting adult rat stem cells into the site of the damaged optic nerve.
"Our hope is to eventually develop arrays of microelectrodes that will allow us to interface the optic nerve with a retinal chip, a bioartificial optic nerve, if you will."
Mallapragada was honored for her polymer research in 2002 by being named one of the world's top 100 young innovators by Technology Review, a technology magazine published the Massachusetts Institute of Technology.
She is also associate director of the Microanalytical Instrumentation Center at Iowa State University.
©Daily Nonpareil 2003