colorful scan of major nerves

Written by Greg Breining

Michael McAlpine just happened to land in the field of regenerative medicine. His real interest is 3D printing.

McAlpine, the Benjamin Mayhugh associate professor of mechanical engineering, has 3D-printed everything from three-dimensional electronics to a soft bionic ear embedded with a conducting silver radio antenna. His current project is a 3D-printed silicon tube that guides the regrowth of nerves in complex patterns.

Each year, about 200,000 Americans suffer significant nerve damage from disease (such as diabetes), accident, or even battlefield injury. McAlpine’s research is funded by DARPA, the Defense Advanced Research Projects Agency, the Army Research Office, and the National Institutes of Health among other sources.

“Nerves are the wiring in your body for transmitting information. That information goes both ways—transmitting sensations to the brain and carrying instructions to extremities for motor function. If nerves are damaged, you can lose the ability to feel or, worse, the ability to move,” McAlpine said.

“The standard fix for a destroyed nerve is to take a healthy nerve from somewhere else in the body and suture it into the cut region and restore function that way. The problem is that you then have to sacrifice a healthy nerve from somewhere else and have a second operation to obtain that nerve,” McAlpine said.

But what if nerves could regenerate themselves? Actually, they can. But their capacity to do so is limited, and they need some help. Here’s where McAlpine’s expertise in 3D printing comes in.

McAlpine used lab rats and scanned their sciatic nerves, the major branching nerves that control the back legs and often serve as stand-ins for studies on nerve injury, regeneration, and recovery. From each scan, McAlpine 3D printed line after line of silicone, building a branched tube of silicone, where the branches exactly matched the branching of the nerves.

He then removed a half-inch section of the rats’ sciatic nerves on one side and sutured the severed ends into the ends of the silicon guide. The rats limped badly at first, as expected. But within three months, the nerves regrew and joined inside the tubes. The rats ability to walk again was improved.

Researchers have used tubes like this before, McAlpine said. But his lab was the first to replicate the nerve branches with a 3D printer. In addition, the 3D printing produced “bonus features.” The process resulted in tiny grooves, which ran the length of the branching tubes. “We used those to our advantage,” McAlpine said. “Those grooves actually tell the nerves which way they are supposed to grow. They grow along those grooves.”

McAlpine also printed “capsules of bio-molecules” such as proteins into the tubes to “facilitate the nerve regrowth. The goal is to direct motor nerves to go one way and sensory nerves to go down the other branch,” he said. “This combination of 3D scanning and 3D printing opens up a whole new avenue.”