Materials 200k
Nature.com
The number of different silks known to exist around the world.
“Different silks have varied chemical compositions and molecular structure organisations, and most importantly, they are manufactured by different organisms,” explains Guan. “For structural materials to be potentially applied in the medical field, silks are required to have superior mechanical properties, and to be relatively easily obtained in reliable quantity and quality. I chose the two commercial silks produced by Bombyx mori and Antheraea pernyi, for which China is the biggest producer in the world.”
The research project for which Guan chose these silks studied the benefits of mixing silk and synthetic polymers to create materials that could be used to manufacture better biomedical implants. Her work has brought into sight a range of new implantable composites with the best properties of both materials, which could enable the creation of structures that hold bone in place after surgery or replace cartilage cushions in the knee.
“It will take at least ten years for it to be finally approved for use as an implantable device, and only if every stage goes smoothly and delivers promising results.”
Juan Guan
“We have investigated various polymeric materials to composite with silk fibre,” she remarks. “A lot of our earlier work used an epoxy resin thermosetting polymer for its easy processability and mechanical robustness. We currently look at polyester, which is biodegradable in vivo and many of them have been approved by the FDA. Combined with these polymers, the silk composite products would be safe for use in the body.”
Guan, who has been investigating natural silks for more than ten years, is impressed both by how successfully these fibres have helped the survival of the species that produce them and by the immense
efforts that have been made to biomimetically produce these silks.
“The natural way of production prototyped by spiders and silkworms is limited when we wish to engineer more complicated shapes and structures,” she says. “The synthetic polymers in silk composites play two roles, an adhesive and a property modifier. I appreciate the invention of silk culture and the value of silk in human culture. Nevertheless, in modern times, the use of natural silks hasn’t been updated to match the need in medicine.” “I believe the combined material can better suit the requirements of implants for specific tissue engineering,” she continues. “The new silk composite materials and structures will be designed to deliver a combination of sufficient mechanical properties, cell and tissue compatibility and to promote tissue repair and function restoration.” The development of composite materials with silk is not an entirely new concept, but previous research has typically used short fibres or the primary protein in silk. In contrast, Guan uses silk fabric woven from a single long thread. Silkworm cocoons contain fibres that can reach almost 5,000 feet in length. Such fibres can distribute mechanical stress more effectively than a series of shorter, discrete ones, Guan reports. “One fundamental attribute of natural silk is its great length to diameter ratio,” she states. “Such a unique property means it can be woven into fabrics 100 microns thin and still retain good strength and other mechanical properties. More importantly, it can be tailor-made to form 3D structures based on extrusion printing techniques.”
The silk and the polymer are combined to form a laminate, which can be cut into custom shapes. Guan proposes that silk composite materials could replace devices based on polycaprolactone (PCL) and polyetherketone (PEEK). She is already working with orthopaedic doctors to create cage- like structures that could replace metal in the process of holding in place vertebrae as they fuse after surgery.
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Medical Device Developments /
www.nsmedicaldevices.com
Ihor Biliavskyi/
Shutterstock.com
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