Screws made of bone-hard biomaterial
Surgeons use interferential screws to fasten crucial ligaments in the knee.
Screws made of polylactic acid (left) and hydroxylapatite (middle) and medical
stainless steel (right). © Fraunhofer IFAM???aural:Bildende???
Titanium is often used for screws applied in surgical operations. The screws usually have to be removed after a while or replaced by new ones. New composites of biomaterials make this unnecessary. They promote bone growth and are biodegradable.
Football players, skiers and tennis players all fear a crucial ligament rupture. If the knee ligaments are damaged, the patient will usually need surgery to restore the joint’s stability. The torn ligament is replaced by a piece of tendon from the leg, fixed to the bone with an interferential screw made of titanium. After a certain time, the patient requires further surgery to remove the material. Now researchers at the Fraunhofer Institute for Manufacturing Engineering and Applied Materials Research (IFAM) in Bremen have developed a screw that is biocompatible and biodegradable.
“We have modified biomaterials so that they can be formed into robust bioactive and absorbable screws with a special injection moulding process,” explains Dr. Philipp Imgrund, head of IFAM’s biomaterial technology department. “Depending on composition, they biodegrade in 24 months.” Biodegradable screws made of polylactic acid already used in surgery can leave holes in the bone when they degrade. The IFAM researchers have therefore developed a mouldable composite made of polylactic acid and hydroxylapatite, the main constituent of the bone mineral. “This composite promotes the growth of bone into the implant,” says Imgrund.
The engineers at IFAM have developed a granulate from the biomaterials that can be precision-processed with conventional injection moulding methods. The complex geometry is achieved in a net-shape process, producing a robust screw with very similar properties to those of real bone. Its compressive strength is more than 130 newtons per square millimetre. Real bone can withstand between 130 and 180.
Contact: Fraunhofer Institute for Manufacturing Engineering and Applied Materials Research, Philipp Imgrund philipp.imgrund@ifam.fraunhofer.de
More information: www.ifam.fraunhofer.de
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