Knee ligament damage is an injury all to common to sportsmen and women. The solution usually involves replacing the torn ligament with a piece of tendon from the leg, which is fixed to the bone by means of a titanium or stainless steel screw. Unfortunately, after a certain time another surgery is required to remove them. Now researchers have developed a screw that is bio-compatible and also biodegradable over time, making this second surgery unnecessary.

Biodegradable screws made of polylactic acid are already used in the medical field, but they have the disadvantage that when they degrade they can leave holes in the bone.

The researchers at the Fraunhofer Institute for Manufacturing Engineering and Applied Materials Research (IFAM) in Bremen developed a moldable composite made of polylactic acid and hydroxylapatite, a ceramic which is the main constituent of the bone mineral. This composite promotes the growth of bone into the implant. Depending on the composition the screws will biodegrade in 24 months.

The screws can be precision made using conventional injection molding methods, meaning there's no need for any post-processing such as milling.

Another advantage of the composite material is that it can be compressed at just 140 degrees Celsius – normally the powder injection mold has to be compressed at much higher temperatures of up to 1400 degrees Celsius.

The team says these screws are close to the properties of real bone. The prototype has a compressive strength of more than 130 newtons per square millimeter. Real bone can withstand between 130 and 180.

The researchers intend to develop other bioimplants using the same energy-saving process.