Bone-hard Biomaterial (IMAGE) Fraunhofer-Gesellschaft Caption Surgeons use interferential screws to fasten cruciate ligaments in the knee. From the left: made of polylactic acid, hydroxylapatite and medical stainless steel. Credit Fraunhofer IFAM Usage Restrictions The picture may be used for editorial purposes only. It is protected by copyright. The use is free of charge if the reference is mentioned. License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.