Silk is a material which has long been recognised both for its beauty and its strength. When stretched, it is a pound for pound match for steel.
Being strong and lightweight it was a natural choice for early parachutes. Before that, both Samurai and Mongol warriors wore heavy silk under armour to protect them against arrows.
Silk is extremely tactile and is much sought after for garments that come into direct contact with the skin. Now for the first time silk may be used inside the body as it is formed into screws to hold bones in place as they repair.
Screws and plates made from metal alloy are often utilised in an operation to hold broken and fractured bones together. A second operation is sometimes required if the metal starts to corrode, with risk of infection and lack of healing. Metal devices that are temporary also facilitate removal in due course.
Biodegradable alternatives are already commonly used but they are more difficult to implant as they are often made from soft polymers that require a hole to be drilled in the bone and a helical ridge or inner thread to be created to hold the screw in position.
American researchers have recently undertaken a trial in which they took pure silk protein and dissolved it in alcohol. They then poured the solution into moulds in the shape of implant fixings, which they then baked. In tests using rats, the silk screws proved strong enough to cut their own thread into bone, like metal screws. The silk screws then biodegraded in the same way as a polymer implant, but without any resulting inflammation.
The scientists anticipate that silk implants may be initially used for facial injuries and eventually for various bone fractures.
Under x-ray, silk screws are invisible – so surgeons will be able to monitor progress easier.
Silk also has the ability to stabilise and release bioactive components. This key advantage makes it possible that in the future, plates and screws made of silk may deliver antibiotics to prevent infection and promote bone regrowth.