maxon Story
Spider silk spins new life into nerve repair
Nerve damage is hard to repair and success rates are relatively low. But now, thanks to the advantages of spider silk, nerve repair has a much greater chance of success. Harvesting silk from live spiders involves a precise technique that demands an exacting drive system to control a low speed, highly accurate winding mechanism.
Spiders can be an uncomfortable presence for many people but thanks to a new development, their silk is set to enhance nerve repair to a level not previously achievable. Newrotex, a medical device start-up with founders from Oxford University, is using spider silk within the human body to support the repair of damage to the peripheral nervous system, covering all nerves outside of the brain and spine.
Nerve damage frequently occurs from trauma and only 60% of people who suffer a nerve injury return to work within a year. Nerve damage can also be caused by reconstructive surgery, such as tumour removal – an acceptable risk, though the consequences of nerve damage can be significant.
Currently, the prospects of recovery from surgery to resolve nerve damage are not positive. The gold standard treatment, known as autografting, sacrifices another nerve from elsewhere in the body to donate to the damaged area. Typically, surgery only results in a return to normal power or nerve sensation in around 50% of cases. There’s also a 27% complication rate from taking the nerve from a donor site, including problems such as chronic wounds and ongoing pain. The treatment also involves nerve loss from another area of the body.
Newrotex Silk Axons - the finished product
Axons spanning the gap
The specific challenge for other attempts to repair nerves with artificial nerve conduits is the difficulty of guiding nerve regeneration across any gap larger than 1cm diameter. When a nerve is cut, the distal nerve ending will die. Axons, the individual nerve fibres, can be regenerated but speed of repair is critical. The body grows its own scaffold bands that nerve connections regenerate along, but it’s a race against time: these bands last for 10 to 14 days before they dissolve. Nerve axons regenerate at a rate of around 1mm per day, so if the connections don’t make it across the gap in time, the nerve will fail to reconnect. Making the task harder still, dead nerve tissue hinders the progress of axon regeneration and subsequent nerve structures forming.
Different approaches have been tried, including implanting cadaver donor nerves, which is expensive and ultimately no more successful than autografting. Techniques to repair the outer conduit tube surrounding the axons also exist, however the success of these implants haven’t proven effective in patients beyond a 1cm gap.
Now, medicine is returning to a technique used over thousands of years for the treatment of wounds. Silk is a durable and biocompatible material, and trials are ongoing by Newrotex to demonstrate the clinical efficacy of using strands produced by spiders as the supporting structure for axon development. To achieve this, spider silk is suspended in a tube that bridges the damaged nerve area, which is held in place by a suture at each end. Nerve axons then grow along the spider silk, enabling reconnection of the nerve. The tube can comprise a hollow tube design already on the market, or from a removed vein, although a bespoke silk version is in development.
The ancient advantages of silk
Significantly improving the prospects of successful nerve repair, the silk remains in place for several months before dissolving, giving the axons support to regenerate over a much longer timespan. The tube also provides a clear, obstacle-free path through which axons can regenerate. This also means the technique could repair nerves over much larger distances than currently achievable – potentially regenerating damaged nerves up to 20cm long. Equally important, this technique could be widely applied.
“Having a completely off-the-shelf solution makes it easy to stitch it in, creating a plug-and-play device. This means patients can get treated more quickly, and you're not relying on a small pool of expert surgeons. Any surgeon working in a specialty where nerves can be damaged could now fix the problem very quickly,” says Dr. Alex Woods, founder and CEO of Newrotex, who is also a trauma and orthopaedic surgeon.
Over time, the tube housing also dissolves along with the silk, leaving just a natural, regenerated nerve in its place. Following demonstration of medical efficacy in numerous animal studies, the first human trial of the product, called Silk Axons, is planned for this summer.
Harvesting the dragline
The harvesting process is complex, combined with the challenge of how to turn the silk from a living spider into a controlled implant that’s safe for humans.
“We use the Golden Orbweb spider because its well-studied, so we already have good awareness about its silk properties and it’s husbandry characteristics, which include a long lifespan and a high quantity of silk production,” explains Alex.
Females of the species grow up to 15cm and weave webs up to a metre wide but Newrotex focuses on the dragline silk that spiders use to suspend themselves with during movement.
“Our interest in the dragline is a result of its dissolvability, the ability for axons to grow along it based on its protein sequences, and the fact that you can reel large quantities of it,” says Alex.
To harvest the silk, a spider is sedated by carbon dioxide and secured on its back with a compact mesh. The appropriate glands of the spider are stimulated, and the arachnids begin to posit the silk.
maxon motor and bobbin
Precision winding
The silk is attached to a custom bobbin and a drive system developed by maxon that carefully winds the silk. The spider is unable to resist the winding motion so it’s a careful balance to manage the silk product to maintain its condition and enable its future use for intricate nerve repair.
“The silk is such a tiny fibre – less than the width of a human hair - so it’s important to tension the reel with precision. As the silk changes from liquid to a solid as it is spun, and its properties are affected by the reeling conditions, control is essential to maintain the core uniform properties for effective repair. Therefore, exact calibration ensuring speed is accurately maintained means we always know the right number and length of fibres have been collected, and that they will remain in the right condition,” explains Alex.
To achieve smooth, ripple-free control of the bobbin, a maxon ironless winding DC motor is paired with a low audible noise gearbox, along with a maxon encoder and speed controller. Central to the process, the speed controller matches actual speed to demand speed, with both speed levels confirmed by a data logger to confirm silk yield, critical for commercial needs and medical regulatory requirements.
Winding with each spider takes place over a defined period of time, with each reeled product resulting in a specific number of silk fibres in one, allowing multiple different product lengths to be collected. At present, Newrotex works with a colony of over 30 Golden Orbweb spiders, with scaling of the colony occurring this year.
“These sessions take place roughly twice a week for each spider, giving time to replace the silk supply and make sure we're not overloading them,” says Alex.
Meeting medical regulations
Critically, the silk has to be turned into a controlled, sterile implant, adhering to medical device regulatory requirements ISO 13485.
“Along with controlled winding, the drive system and bobbin frame can be cleaned and held in a sterile environment while working with a spider,” says Alex. “To avoid the spider itself invalidating a clean room standard, we use environmental-controlled hoods. After the procedure, the apparatus is cleaned, and the drive system is sterilised.”
With extensive human trials planned for later in 2025, Newrotex aims to offer its nerve repair treatment to first patients in 2027. In time, the development also has the potential to be applied to central nervous system regeneration.
Images © Newrotex Ltd.