Surface Modification of Biodegradable Magnesium-Calcium Implants by Burnishing

Magnesium-Calcium (MgCa) alloys have shown very promising potential to make biodegradable metallic orthopedic implants. Biodegradable metallic implants relieve the need for second surgery and avoid stress shielding common with permanent metallic implants. Moreover, they provide enough strength in load carrying orthopedic applications as opposed to polymeric counterparts. High degradation rate of these alloys is the pressing issue resulting in subcutaneous hydrogen bubbles and high pH values and ultimately imbalance in physiological reactions. Surface modification techniques has been implemented to enhance the biocompatibility of these alloys by matching their corrosion rate with bone healing rate and absorption rate of corrosion by-products. Low plasticity burnishing (LPB) is a novel technique that makes wide range of surface integrity characteristics and consequently corrosion rates attainable. This is instrumental in developing proper degradation rates with respect to local healing and absorptions rates present in each application. Besides, LPB can be applied on already available CNC machining centers and in that sense is very flexible. Hence, studying the effects of LPB process parameters on surface integrity is important. In this paper, effects of burnishing passes and their pattern on surface topography, surface roughness, surface/subsurface microhardness, microstructure, and surface residual stresses of MgCa0.8 (wt%) implants are investigated.