Silk is tougher than it looks. Weight for weight, the shiny stuff is as strong as steel when stretched â€“ and now it seems it can also be fashioned into screws so tough that they can cut through bone.
Metal alloy screws and plates can hold fractured bones together but if they start to corrode a second operation is required to remove them. Biodegradable alternatives can trigger inflammation and are time-consuming to implant â€“ the polymers are so soft that you first have to drill a hole in the bone and fashion a helical ridge around the inside – the inner thread – to hold the screw in place.
Samuel Lin at the Harvard Medical School and David Kaplan at Tufts University in Medford, Massachusetts, wondered if silk screws and plates could work better. To find out, they dissolved silk in alcohol, poured the solution into moulds shaped like the implants and baked them.
In rats, the team found that their silk screws were tough enough to carve their own threads into bone as they are screwed into a hole, just as metal alloy screws do. The silk naturally biodegrades with time, like the polymer alternatives but without causing inflammation.
“Clinical trials will hopefully begin in the near future,” says Lin.