As Engineering celebrates its Oxford centenary, Michael Gross finds scientific collaboration resulting in unexpected spin-offs.
For Fritz Vollrath, pulling threads out of a spider’s backside is an entirely normal thing to do, to the extent that he talks about ‘silking’ a spider as a farmer would about milking a cow. Having specialised on spider and insect silks for more than 25 years, Vollrath has pioneered many new ways of studying these natural materials and has also helped to push application projects forward.
Investigations by his lab in Oxford’s Department of Zoology and elsewhere have shown that spider silk is tougher than any artificial fibre that humans can produce so far, including Kevlar. However, it is also extremely elastic. ‘I could make you a bullet- catching vest from spider silk,’ Vollrath offers as an illustration, ‘but it would stop the bullet after it has gone through your body, so it wouldn’t be much use.’ For the same reason, trying to build suspension bridges or space elevators from spider silk wouldn’t make much sense.
What would make sense, however, would be to use spider silk in medical textiles and in tough composite materials. In a medical context, spider silk has the advantage – apart from being very tough – of being biocompatible, integrating very well in the living organism, and stimulating cell adhesion. ‘For these reasons, biomedical applications are our first point of call’, says Vollrath.
As one of the founders, Vollrath is involved with the company Oxford Biomaterials Ltd, which develops ideas for silk-based products and then initiates further spin-out companies to commercialise them, but retains all interests in the basic silk platform technology. So far, OBM has spawned Neurotex Ltd, which develops silk-based tissues as substrates for nerve cells to grow on, ultimately enabling surgeons to repair damaged nerves, and SuturOx Ltd, which specialises in threads for surgical sutures. A third company, to be set up soon, will be Orthox, specialising in bone and knee repair.
Some of Vollrath’s latest research, which aims at improving tendon repair, is in collaboration with andy Carr, Nuffield Professor of Orthopaedic Surgery at the Nuffield Orthopaedic Centre, where the ‘Oxford Shoulder and Oxford Knee’ were developed. Ideally, Vollrath says, surgeons will be able to apply a repair patch that has been made to match the mechanical properties of the body’s own tissues. There is a trend, apparently, towards ever younger patients requiring these operations. With suitable silk patches, Vollrath hopes that the deterioration of the joint can be stopped before the bone itself gets damaged and an artificial replacement has to be built in. Collaborations with the biomechanics groups of the University’s Engineering department – currently celebrating its centenary – will be important for this kind of work in order to tune the silks to match exactly the mechanical and material requirements of the different joints.
Carr and Vollrath are jointly supervising a project funded by the Jean Shanks foundation and the Lord Nuffield Trust, which aims to produce silk-based tendon and bone that can be used to improve the success of rotator cuff tendon repair surgery at the shoulder joint. Professor Carr says that 20–30 per cent of the population suffer from shoulder pain that is bad enough for them to consult their family doctor. This makes shoulder pain the second most common orthopaedic problem after back pain. Most of the pain is due to fatigue and tearing of tendons.
Commenting on the treatment options available today, Carr explains that the success of current surgical techniques, including keyhole operations, is frustrated by the poor state of the tendon tissue. Therefore, he says, ‘we are very excited by the possibility of using silk materials to enhance the tissue we repair, in order to improve the result and outcome for the patient. The main problem is developing something that has the necessary mechanical strength and will integrate with the body’s own tissues, in this case tendon and bone.’ One of the challenges is that the artificial tendon also needs to last and function like a normal tendon, possibly over many decades. The researchers hope to have a product ready for use in patients within the next five years.
But where will all the silk come from? Unlike silk moths, web-building spiders tend to have aggressive territorial behaviour, so they are not the easiest animals to farm in large numbers. and if they need to be silked by hand, that would make the resulting material rather expensive.
Many attempts have been made to produce spider proteins in other organisms and then produce artificial spider silk. So far, these have all failed, and in a research paper published in spring 2007 Vollrath’s group has shown why. Studying the flow properties (rheology) of such reconstituted silk dope, the researchers showed that it differs fundamentally from the dope found in the specialised organs of a living spider. ‘The differences are in kind, not just in degree’, Vollrath says. Thus, after decades of research, humans are still unable to match the spider’s achievement.
A way out of this dilemma, Vollrath suggests, is to go back to worms and use their biological variety. The silk worm, Bombyx mori, isn’t exactly typical of what’s on offer in nature. ‘The silkworm is like a specialist milk cow’, Vollrath explains; ‘it is shaped by 6,000 years of domestication.’ Studying other insects, researchers have identified other worms that have very strong silks, which, with some chemical modifications, could perhaps be tuned to match the properties of spider silk, while being easier to obtain from the biological source.
So when will medical practitioners be able to buy spider or spider-like silk to repair shoulders or nerve cells? This field has seen much promise and disappointment over the years, but Vollrath is still optimistic that such silk products for medical applications will be commercially available by 2010. at least by then, he will no longer have to do the silking.
Michael Gross is a science writer based in Oxford.