The Nerve of It All

3D technology could one day address severe damage

Have you ever had to wait for the feeling to return in a limb that has “fallen asleep” before being able to use it again? If so, you have experienced for a brief moment what it is like to have peripheral nerve damage.

The numbness of your sleepy foot is caused by compression of the nerves and disruption of their ability to carry information to and from the limb.

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The effects of nerve compression, luckily, are only temporary. The feeling will return to your foot after a short while.

But, in cases of disease and trauma, nerve damage can lead to permanent disability.

Many of the 20 million Americans suffering the debilitating effects of damaged nerves are military officers and veterans. Additionally, some 2.8 percent of all trauma cases result in peripheral nerve damage, which affects areas outside the central nervous system, like arms and legs.

Many of the 20 million Americans suffering the debilitating effects of damaged nerves are military officers and veterans.

Think of a nerve as a conduit of wires. Some of the wires in the bunch send commands from your brain to your muscles. Others shuttle sensory information from your extremities to your brain. But, when a nerve is crushed or severed, the communication pathway is destroyed. The muscles don’t know what to do, and your brain doesn’t register any sensation from the part of the body that lies beyond the damaged nerve.

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Sometimes damaged wires, called nerve fibers, regrow without intervention, and limbs regain the function and feeling that was lost.

But more often, treatment of nerve injuries requires surgeries.

If the injury was a clean cut, and the ends of severed nerves are located close to one another, doctors can simply suture the ends together. However, if a larger segment of nerve is damaged, it may require the graft of a nerve taken from another part of the body.

Nerve grafts don’t always work, and can result in numbness and sometimes pain, or other problems in the area from which the transplanted nerve was taken.

Right now, nerve grafts are the gold standard for treatment when the length of the damaged nerve exceeds 5 millimeters — a seemingly miniscule distance. Yet researchers have been working on another solution that involves creating specialized biomedical devices for nerve regeneration, called artificial “nerve guide channels,” or NGCs.

In effect, NGCs are a tubular scaffold that direct regrowth of nerve fibers. Their use in a clinical setting has been met with some success, but they have not yet surpassed the outcomes of grafts.

Because of the way they are manufactured, NGCs are limited to treating short linear segments of damage. Yet, injuries often involve more complicated nerve geometries than a straight line. So, being able to customize the design of an NGC based on the complexities of an individual’s damage has the potential to benefit many previously untreatable injuries.

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A recent advance suggests that this kind of personalization of treatment might be possible in the not-to-distant future.

A multi-institution team led by researchers at the University of Minnesota and Johns Hopkins University published a study demonstrating that 3D scanning and printing can successfully produce NGCs that enable the regeneration of a small nonlinear segment of a nerve in a living animal.

They used a custom 3D printer to print a geometrically exact silicone replica of the hollow nerve pathways.

First, the team used a structured light scanning technique to create a 3D image of sections of sciatic nerve removed from rats. The nerve was sectioned at the point where the motor nerves split off from the sensory nerves to create two individual nerve tracts, or a branching pattern.

Then, with that image, they used a custom 3D printer to print a geometrically exact silicone replica of the hollow nerve pathways. In the process, the printer also covered the interior of the silicone scaffold with nerve growth stimulating chemicals specific to getting sensory and motor nerve fibers to grow.

Once the scanning and printing processes were complete, which only took about an hour, the customized NGCs were implanted back into the rats. Within three months, the rats regained much of the function that was lost when the section of sciatic nerve was removed.

“Someday, we hope that we could have a 3D scanner and printer right at the hospital to create custom nerve guides right on site to restore nerve function,” said Michael McAlpine, the lead author of the study and an associate professor of mechanical engineering at the University of Minnesota.

From there, it’s not a big leap to imagine the same set-up in battlefield hospitals.

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The next step is to try it in humans, but it faces an uphill battle before it’s used in hospital operating rooms. Not only does the method need to be approved for clinical use by the U.S. Food and Drug Administration, but the materials involved still need to be proven effective and safe.

“The most significant advance of this paper is the capability to print multiple materials together with neurotrophic growth factors. From a pre-clinical research standpoint, this is a nice advance,” said Scott Hollister, a UM professor of biomedical and mechanical engineering at the University of Michigan, who was not involved with McAlpine’s study.

Hollister, however, did make waves recently for 3D scanning and printing customized artificial tracheas for children diagnosed with life-threatening tracheomalacia.

An upgrade to the gold standard for nerve grafting and regeneration can’t come soon enough — not for the many wounded veterans for whom nerve injury has placed them “out of touch” with their physical surroundings, nor for the many civilians who suffer nerve damage from a variety of causes.

The daughter of a World War II Naval Reservist, Leela Pratt is no stranger to the struggles that accompany severe nerve damage. She was diagnosed with nondiabetic small fiber peripheral neuropathy for which, she told Lifezette, the doctors couldn’t determine an origin.

“There was an enormous amount of pain,” she said. “People knew people who had the same thing. One had her feet amputated; another committed suicide. I couldn’t sleep or eat.”

Now, thanks to a combination of treatments, she has gotten her life back after years of debilitating pain. Told of the advances in 3D printing, she expressed wonder — and hope — that the technology would save others from the suffering she endured.