Complex nerve injuries are a challenging problem for the medical fraternity, as their reattachment and regrowth is a fraught and delicate process that is very rarely successful. Overcoming these difficulties, however, would mean that a cure for debilitating conditions like paraplegia, quadriplegia and other forms of paralysis may one day be found. In this vein, US researchers have created the first-ever 3D printed guide specifically designed to assist in the regrowth of the sensory and motor functions of complex nerves.

Hundreds of thousands of people each year are afflicted with a crippling nerve injury or disease that leaves them partially or wholly paralyzed. As a result, many techniques to reattach or regrow severed or withered nerves have been tried over the years, but such things as enzymatic modification or gene manipulation are largely ineffective at growing nerves across large areas of damage, or are difficult to repeat with certainty.

To help solve these problems, researchers from the University of Minnesota, Virginia Tech, University of Maryland, Princeton University, and Johns Hopkins University collaborated on a ground-breaking procedure to produce a 3D-printed silicone support structure that is implanted into living tissue to guide and encourage nerve growth and reattachment. Replete with a range of biochemical "cues" designed to enhance and nurture nerve cell formation, these devices have been successfully tested in the bodies of living rats in a laboratory.

Specifically targeting the sciatic nerve (the largest and longest nerve in most mammals – including humans – that generally controls the muscles of the thigh, lower leg, and foot) the researchers employed a 3D scanner to intricately map the arrangement of this nerve in a rat. Following this, the researchers fed the information into the software used to control a custom-built 3D printer which then produced the silicone nerve guide. The sciatic nerve in the rat was then severed, and the guide was surgically implanted into the rat by grafting it to the sliced ends of the nerve. After a period of around 10 to 12 weeks, the rat regained much of its ability to walk again.

"This represents an important proof of concept of the 3D printing of custom nerve guides for the regeneration of complex nerve injuries," said the study’s lead researcher, University of Minnesota mechanical engineering professor Michael McAlpine. "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."

All-in-all, the scanning and printing process requires little more than an hour to achieve, say the researchers, but the nerves require several weeks to grow back. Professor McAlpine points to preceding research of a similar nature and time to regrow direct lines of nerves in the laboratory, however this is the very first time that the creation of a bespoke support guide for the regrowth of complex, Y-shaped sensory and motor branch axon bundles found in the sciatic nerve has been achieved.

"The exciting next step would be to implant these guides in humans rather than rats," said Professor McAlpine.

In circumstances where a nerve is already severed or otherwise missing, as would be most cases in nerve damage patients, the researchers believe that a "library" of stored nerve scans collected from other patients or cadavers could be used as proxies to create 3D-printed guides for patients suffering from nerve injury.

The short video below shows the 3D printing process used for the production of the silicone guides.

The results of this research were recently published in the journal Advanced Functional Materials

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