It is imperative that biodegradable magnesium alloys have sufficient mechanical strength and controlled degradation in vivo to ensure clinical viability. While it is known that mechanical and environmental parameters affect magnesium degradation, little is currently known about the exact in vivo conditions. A fully-implantable measurement system was developed and used to record temperature and strain in vivo. This may increase the understanding of in vivo degradation mechanisms and provide valuable data to improve magnesium-based implants that has so far not been available.

Biocompatible permanent implants are the gold standard for osteosynthesis. However, these materials induce stress-shielding by reducing loading-induced bone remodeling that leads to bone loss and increases the risk of peri-implant fractures. In elderly people decreased bone mass and density increases the risk of fractures. Moreover, one out of five men and one out of three women suffer from fragility fractures associated with osteoporosis. Thus, this group of patients may gain from an alternative material. Osteoporortic, old healthy and juvenile healthy Sprague Dawley® rats underwent bicortical implantation of ZX00 pins into the metaphyseal tibiae. Implant and gas volume were calculated after micro-CT. Enhanced ZX00volume loss was observed in OVX and old compared to juvenile rats. Gas evolution was significantly increased in OVX compared to juvenile rats. THe underlying mechanism needs further elucidation.

Mg-based implants demonstrate biocompatibility, bioresorbability, and good mechanical features. However, due to the low mechanical strength and fast degradation rate with the release of gaseous hydrogen of pure Mg, its application in clinics is limited. Hence, extra-high purity Mg and, especially, Mg alloys might overcome disadvantages associated with pure Mg. Released degradation products also affect cellular activities such as cell proliferation, differentiation, attachment, and eventually support bone growth and fracture healing. Therefore, it is important to understand the degradation behaviour of Mg-based implants and their effect on bone remodelling. In this study, we investigated i) the degradation properties of ZX00 (Mg<0.5wt%Zn<0.5wt%Ca), extra high-purity Mg (XHP-Mg) and state-of-the-art titanium (Ti) pins and ii) their effects on bone in-growth in Sprague Dawley (SD) rats. Material degradation was observed via in vivo low-medium resolution (2, 6, 12, 18 and 24 weeks after surgery) and ex vivo high resolution micro-computed tomography µCT (µCT; 6 and 24 weeks after surgery). Implant volume and surface, gas volume, and bone volume were evaluated with Mimics software version 22. Animals were sacrificed after 6 and 24 weeks, respectively. Bone marrow stromal cells (BMSCs) were isolated and characterized to be used for gene expression analysis. Our preliminary results showed that ZX00 had an adequate, monotonous degradation performance with an increased hydrogen gas evolution 12 and 24 weeks after implantation. We expect that ZX00 is superior to XHP-Mg, especially concerning degradation performance and hydrogen gas evolution. Moreover, isolated BMSCs showed differentiation into other mesenchymal lineages osteogenic, chondrogenic, and adipogenic, demonstrating stem cell like features. In gene expression analysis, we expect that degradation products of ZX00 have a positive effect on upregulation of the osteogenic gene markers, indicating the enhancement of bone growth.