Examination of biodegradable magnesium screw processed by equal channel angular pressing: A novel in vivo study in rabbits

Magnesium alloys have shown potential as biodegradable metallic materials for oral and maxillofacial surgery applications due to their degradability. Biodegradable magnesium are advantageous over existing biodegradable materials such as polymers, ceramics and bioactive glasses in load-bearing applications where sufficient strength and Young's modulus close to that of the bone are required. However, fast degradation of magnesium due to corrosion in the human bio-environment may limit its clinical applications, for example, oral and maxillofacial surgery applications, because a too high degradation rate leads to premature deterioration of biofunctionality. Equal channel angular pressing (ECAP) is a viable forming procedure to extrude material by use of specially designed channel dies without a substantial change in geometry and to make an ultrafine grained material by imposing severe plastic deformation. In this study we use Mg alloys processed by Equal Channel Angular Pressing (ECAP) for screw fabrication products. We developed an in vivo model in rabbits to assess Mg ECAP alloys degradation for oral and maxillofacial surgery applications. Four screws were implanted to the right femur of each of 9 rabbits. This group was divided into observation periods of 4, 12 and 20 weeks. Alloy degradation and biological effect were determined by micro-computed tomography (micro-CT) and histological staining after sacrifice the rabbits. The results of this novel study in rabbits indicates that this screw Mg ECAP should be considered as an alternative to conventional implant materials.