Feb. 24, 2015

Researchers at the University of Sheffield have succeeded in helping nerves damaged in traumatic incidents repair themselves using a 3D printed guide.

The team used the device to repair nerve damage in animal models and believe the method could be used to treat many types of traumatic injury in humans.

Patients with nerve injuries can suffer complete loss of sensation in the damaged area, which can be extremely debilitating. Current methods of repairing nerve damage require surgery to suture or graft the nerve endings, a practice which often yields imperfect results.

The device, called a nerve guidance conduit (NGC), consists of a framework of tiny tubes, which guide the damaged nerve ends towards each other so that they can repair naturally.

Although some NGCs are currently used in surgery, they can only be made using a limited range of materials and designs, making them suitable only for certain types of injury.

The technique, developed in Sheffield's Faculty of Engineering, uses Computer Aided Design (CAD) to design the devices, which are then fabricated using laser direct writing, a form of 3D printing that builds up tiny blocks of materials into a 3D structure. The advantage of this is that it can be adapted for any type of nerve damage or even tailored to an individual patient.

(a) Optical and (b) scanning electron microscopy images of typical PEG nerve guidance conduits of 5 mm in length × 1.5 mm in diameter and a wall thickness of 250 μm (used in the in vivo analyses). (c) and (d) SEM images of a set of trenches 5 mm long, written with 5 mW laser power and a write speed of 0.01 mm/s, (c) at a magnification of 13× and (d) 200×. (e) An experimental PEG nerve guide made with a wall thickness of 50 μm to illustrate the resolution capability of microstereolithography.

(a) Implantation of a 5 mm × 1.5 mm × 250 μm PEG guide in to a THY-1-YFP-H common fibular mouse small gap 3 mm injury model. (b) Thy-1-YFP-H nerve graft repair image. Analysis method illustrating intervals marked with sample axon tracing from 4.0 mm interval position back to 0.0 mm (start) interval. The number of axons at each interval were counted and compared with a −0.5 mm interval (not shown) to obtain a sprouting index value; axons were traced from distal intervals back to 0.0 mm or a branch point with a previously traced axon (as highlighted in expanded sections with green circles) to calculate percentage of unique start axons represented at each interval.

Enlarged view at the interface between the proximal nerve ending and graft. Traced axons were measured and lengths compared with a direct route from 0.0 mm to 1.5 mm to determine an average increase in length.

Researchers used the 3D printed guides to repair nerve injuries using a novel mouse model developed in Sheffield's Faculty of Medicine, Dentistry and Health to measure nerve regrowth. They were able to demonstrate successful repair over an injury gap of 3mm, in a 21-day period.

"The advantage of 3D printing is that NGCs can be made to the precise shapes required by clinicians," says John Haycock, Professor of Bioengineering at Sheffield. "We've shown that this works in animal models, so the next step is to take this technique towards the clinic".

The Sheffield team used a material called polyethylene glycol, which is already cleared for clinical use and is also suitable for use in 3D printing. "Further work is already underway to investigate device manufacture using biodegradable materials, and also making devices that can work across larger injuries" says Dr Frederik Claeyssens, Senior Lecturer in Biomaterials at Sheffield.

"Now we need to confirm that the devices work over larger gaps and address the regulatory requirements," says Fiona Boissonade, Professor of Neuroscience at Sheffield.

The research, published in the journal Biomaterials, was funded by the Engineering and Physical Sciences Research Council and the Medical Research Council.



Posted in 3D Printing Applications


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