Bone-Hard Biomaterial Could Replace Surgical Titanium Screws

A biocompatible and biodegradable anchoring screw could spare cruciate ligament surgery patients further surgery to remove the interferential screws used to repair the torn ligament.

Researchers at the Fraunhofer Institute for Manufacturing Engineering and Applied Materials Research (IFAM; Bremen, Germany) developed a moldable composite made of polylactic acid (PLA) and hydroxylapatite (HA, a ceramic which is the main constituent of the bone mineral). The granulated biomaterial can then be precision-processed using conventional injection molding methods, obviating the need for any postprocessing such as milling. The complex geometry required is achieved in a net-shape process, producing a robust screw possessing biomechanical properties that come very close to those of real bone. The compressive strength of the prototype screw was measured at more than 130 N/mm², which is comparable to real bone that can withstand between 130 N/mm² and 180 N/mm².


"We have modified biomaterials in such a way that they can be formed into robust bioactive and resorbable screws by means of a special injection molding process,” said Philipp Imgrund, Ph.D., head of the biomaterial technology department at IFAM. "This composite possesses a higher proportion of hydroxylapatite and promotes the growth of bone into the implant; depending on the composition they biodegrade in 24 months.”

PLA is thermoplastic, biodegradable, aliphatic polyester derived from renewable resources, such as cornstarch or sugarcane. Although PLA has been known for more than a century, it has only been of commercial interest in recent years, in light of its biodegradability. However, while biodegradable screws made of PLA are already used in the medical field, they have a distinct disadvantage, since when they degrade they can leave cavities in the bone.

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Fraunhofer Institute for Manufacturing Engineering and Applied Materials Research