Materials
ilk is a remarkable material, the full properties of which are still being brought to light. It is everywhere in nature – more than 200,000 different silks are currently known to exist – and at a time of growing concern about ecological damage and depletion of non-renewable resources, demand for silk as a structural material made from renewable resources is growing fast. In the medical field, its use is well-established. Silk scaffolds have been used successfully in wound healing, sutures, and in tissue engineering for bones, cartilage, tendons and ligaments. So what makes it such a versatile material? Principally, its strength. Spider silk, for example, is five times stronger than steel at equivalent weights, and an analysis of the venomous brown recluse spider using an atomic force microscope has shown this is because its strands – each of which is 1,000 times thinner than a human hair – are made of thousands of individual nanostrands 20 millionths of a millimetre in diameter, coiled together like a cable. Silks are a family of structural proteins that are not only strong, but highly biocompatible, degradable and versatile in their application. They are amenable to aqueous or organic solvent processing, and can be chemically modified to suit a host of biomedical applications. Silk biomaterials are biocompatible when studied in vitro and in vivo, eliciting little or no host-immune response.
Silk to touch S
“Silk has been used as a suture for centuries,” says Juan Guan of the School of Material Science at Beihang University’s Advanced Innovation Center for Biomedical Engineering. “It has a high specific strength and might be the only micrometre-thin continuous fibre before the invention of synthetic polymer fibres. The protein composition makes silk safe for use in the body, and its combinatorial properties of strength, toughness and resilience make it a strong candidate as a structural biomaterial.”
One name, many materials Silks come in many different types and from various species, all having specific properties. Spider silk, woven into intricate webs, is familiar to us all, but there is also silkworm silk from the larva of the Bombyx silk moth, which can be farmed in large numbers and create a silk frequently used in textile production. Then there is silk from bagworm moths, which create a protective case made of silk and other found materials from their environment, such as sand or plant materials. Bagworm silk, particularly from the largest and heaviest Japanese bagworm (Eumeta variegata) could be among the strongest silks investigated to date, though much research still needs to be done into its various mechanical and physical properties.
Nowadays, silk has a multitude of applications beyond the luxury clothing and other decorative products for which it’s famous, and that includes applications in the medical device sector. In order to create silk-based products, however, the natural substance is increasingly being combined with man-made polymers. Jim Banks looks at the latest research and asks Juan Guan of Beihang University how silk combines with other materials to enhance its natural properties, and what potential applications this might have in the clinic.
Medical Device Developments /
www.nsmedicaldevices.com
89
Ihor Biliavskyi/
Shutterstock.com
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