Tubes manufactured from natural silk could provide a promising tool for the repair of large gap nerve injuries, according to a new study.
Researchers from the University of Oxford, UK, and MedUni Vienna, Austria, developed the novel method to produce nerve guides that could guide the growth of nerve fibres and cells across bigger gaps.
At the moment it is only possible for nerve guides to bridge very small distances because of the lack of an internal framework to act as a “handrail” that regenerating tissue can use to grow on.
Human nerve injuries with large gaps are often treated by autografts, but this process has drawbacks, including a limited availability of donor nerves, lengthy operations, and the possibility of further harm for the patient.
In Advanced Healthcare Materials, the research team say they have developed a nerve guide using two different types of natural silk: the tube wall is made from silk produced by silkworms (Bombyx mori), while the inside filled with dragline silk fibres from golden orb-web spiders (Trichonephila edulis).
When the tubes were tested in rats whose right sciatic nerve had been cut, which had left a 10mm gap, they found the damaged nerves adapted to the novel silk nerve guides and grew along the silk threads until the severed endings successfully reconnected.
Using advanced microscopy techniques to analyse the healing process, the team showed how the silk tubes had a highly porous structure, which allows nutrients and waste materials to be exchanged.
They also saw that Schwann cells, the key drivers of peripheral nerve regeneration, adhered strongly to both the tube walls and the dragline silk fibres, and migrated quickly at more than 1.1mm per day).
Co-author Professor Fritz Vollrath said: “Animal silks offer exceptional mechanical and biological properties and versatile manufacturing possibilities to assist the re-engineering of tissue. Our advanced silk-in-silk nerve guides combine the excellent ability of silkworm silk to be processed into three dimensional structures with the outstanding cell adhesion qualities of spider dragline silk.”
The authors said using natural materials for nerve guides has many advantages over synthetic substances. For example, spider silk degrades and produces hardly any immune response in animal models. They are also abundant, with a single harvest from an orb-web spider yielding about 10m of silk, enough to fill a 10mm long nerve guide.
The team hopes to develop the silk nerve guides into an “off-the-shelf” solution to treat nerve injuries in humans.
Semmler L, Naghilou A, Millesi F et al. Silk-in-silk nerve guidance conduits enhance regeneration in a rat sciatic nerve injury model. Advanced Healthcare Materials January 2023; doi: 10.1002/adhm.202203237
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