Degradable implants made of magnesium alloys

The article presents results of an interdisciplinary project focusing on the development of degradable magnesium-implants. Those implants do not need to be removed after the healing process and therefore provide a huge benefit for patients and the health care system. Different magnesium fracture-screw designs are investigated. Furthermore, the influence of the machining on the surface and subsurface layers of the specimen is analysed. In laboratory corrosion tests AZ91 samples show a strong local corrosion attack. A more homogenous corrosion attack is observed on Magnesium-Calcium-alloys, which suggests that this alloy is more suitable for degradable implants. However, the corrosion resistance of the investigated magnesium alloys still needs to be increased significantly. The implant geometry has to be adapted to the material loss during in vivo degradation. Degradable Implants Annually around 5.5 Mio. accidents occur in Germany causing bone fractures [1]. Approximately 10% of those fractures are too complex to be simply medicated externally and thus have to be fixated by surgical bone implants. Traditional methods of osteosynthesis or osteotomy use metal implants made of steel or titanium. Durable implants represent a foreign body, bearing the enduring risk of a local inflammation. Furthermore they permanently protect the healing bone against mechanical exposure. This effect called stress-shielding obstructs the stabilization of the bone tissue that needs mechanical loads to obtain and maintain its rigidity. To avoid those negative effects annually about 300.000 revision surgeries have to be performed, in which the implants are excised, causing the risk of a refracture and additional days of after-treatment. Expenses exceeding 500 Mio. € annually have to be incurred by the national health care system [2]. Degradable, biocompatible implants, which dissolve in the human organism represent an appropriate solution. Currently used absorbable materials are different poly-lactides. However, these materials have unsatisfactory mechanical properties as cortical-screws. Magnesium as an Implant Material Previous in vivo studies have shown that magnesium alloys may be suitable as degradable biomaterial for use in medical implants [3]. The mechanical properties of magnesium are superior to poly-lactides by far, but still inferior to surgical steel or titanium alloys. The characteristic values are dimensionally comparable to the cortical bone substance. That could even reduce the negative effects of stressshielding. Furthermore magnesium as an essential component of the human body is biocompatible. The base character of the element with an electrochemical