Fibres of the future
Spinning success out of silk
21 December 2011
It may seem quite a step from a beautiful and sensual fabric to an artificial knee, but researchers are looking to the natural world to create a new breed of exotic materials for biomedicine based on silkworm and spider silk.
Silk is a superb material: light, strong, and highly elastic. Scientists studying the fundamental properties of this natural substance have now formed a number of, ahem, spin-out companies to develop a new generation of biomedical implants.
Silk fibres are obtained from the cocoon of the B. mori silkworm. Image: Oxford Silk Group (OSG)
The developments follow a BBSRC research grant that began a decade ago to investigate spider and silkworm spinning technology. "In effect the grant provided important background to a prior patent application – now granted – that was instrumental in the business plan for our first spin-out Spinox," says Professor Fritz Vollrath of the Oxford Silk Group (OSG) based at the University of Oxford who led the study.
The Silk Road
Beneath silk's attractive and elegant exterior lurk a wealth of intricate properties. It has a nanocomposite structure, meaning the combined material has different properties than the individual parts, and this small-scale complexity provides its unique physical properties. It can also be washed and treated from the raw form to fine tune its material properties from super-strong to specifically biodegradable. Silk is also biocompatible, and thus makes an ideal substrate to use inside the human body for as advanced biomedical implants.
So how do you turn silk into new knee cartilage, for example? The details of Spidrex – the name of the new silk-based material – are a closely guarded commercial secret, but Vollrath reveals that Spidrex is manufactured by a proprietary [protected] process which uses rigorous yet gentle cleaning of both silk filaments from mulberry and non-mulberry silkworm silks. "Intimate knowledge of beneficial amino acid sequence and morphology in non-mulberry silks allied to an advanced understanding of silk protein processing, based on studying spider silks, has led to the combination of excellent mechanical and tissue regenerative properties found in Spidrex devices."
Vollrath's team and colleagues have founded a number of companies to develop and commercialise Spidrex as well as other silk-based products. Orthox, for instance, casts silk into shapes suitable for use in replacement joints. Because the silk implants do not irritate or harm the body's cells, they not only provide tough replacement surfaces but also encourage regrowth of new tissue.
Another spin-out, Neurotex, uses fine filaments of silk to bridge gaps in damaged nerves – just as a trellis supports a plant's growing tendrils. Vollrath says the Spidrex filaments provide a guide for (to direct) regenerating nerve cell processes and Schwann cells, which work to transmit impulses along the axon of a nerve cell, to migrate quickly across a traumatic injury. Their experiments show that severed nerves grow along the biocompatible silk filaments and the binding and migration of these two cell types is thought to be promoted by the unique properties of Spidrex filaments (ref 1).
"These include high biocompatibility due to the nature of the silk protein sequence which is enhanced by our additional proprietary treatments, micro-textured surface composed of highly orientated and closely packed nanofilaments," says Vollrath. He adds that a high density of naturally occurring integrin [receptor] binding sites on the silk molecules encourage human cells to seek the neighbourhood of the silk and may even encourage growth. Importantly, a relevant patent for silks in nerve regeneration has just been granted also in the USA thus adding to a number of other key countries.
Both Orthox and Neurotex technologies have shown great promise in preclinical trials, and will hopefully soon enter full clinical trials. In addition, more relevant patents have been granted thus protecting intellectual property (IP). Importantly, along the way many additional inventions as well as sources of funding (see below) are being utilised to take the OSG's technology forward.
For example, Vollrath's team have also developed an innovative silk reeling method to collect high grade silk from wild silk worms (ref 2). This new technology is poised to stimulate novel silk industries based not only in the UK but importantly raise productivity of silk markets in developing economies around the world. "The new insights could in turn help to reduce rural poverty and provide an incentive for preserving and planting silkworm food plant trees leading to considerable environmental advantages," Vollrath explains. "In late 2011 we are currently applying for a BBSRC Follow-on fund to demonstrate the possibility of scale-up of wild-silk reeling knowhow, the development of which was part-funded by a BBSRC CASE studentship to PhD student Tom Gheysens."
In fact, scientists at the OSG believe that silk is a material of the future. Not just intricate garments and medical implants, but the basis of a broad range of objects from car panels to bike tyres. And why not? Silk is sustainable, natural, environmentally friendly, and can potentially provide a wealth of green jobs. Combined with its superb material properties, it is a material hard to beat.
In addition to funding by BBSRC, the OSG's research has also been funded by The European Research Council, the European Commission, the Engineering and Physical Sciences Research Council and the US Air Force Office of Scientific Research.
- Regenerative potential of silk conduits in repair of peripheral nerve injury in adult (external link)
- Demineralization Enables Reeling of Wild Silkmoth Cocoons (external link)
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