The Comparability of In Vitro and In Vivo Experiments for Degradable Mg Implants

Mg implants possess a great potential for clinical applications. Thousands of patients are already successfully treated with Mg implants and the number of approved products increases. Despite the fact that the implants generally work, we know that we have not yet reached a full understanding of all processes which occur during the degradation of the material and tissue regeneration. A prerequisite for a comprehensive description is the visualization and analysis of the in vivo processes with high resolution, while avoiding metal artefacts during imaging and taking care of different imaging properties of inorganic and organic matrices. Here, synchrotron radiation-based micro-computed tomography was utilized to determine the degradation rates for two implant materials (Mg-5Gd and Mg-10Gd, wt. %) in vitro and in vivo. The comparison for in vitro and in vivo degradation in terms of degradation rate and pitting factor shows that in vitro experiments predict in vivo results the error. As a second aspect, push-out experiments revealed a better integration into bone for Mg-10Gd and the improvement of implant stability over time. Finally, micro X-ray fluorescence spectrometry was applied to determine the elemental composition of degradation products around the Mg-5Gd specimen in vivo. This technique shows that the Mg content of the degrading specimen is decreasing while the Gd content stays constant.