gms | German Medical Science

Objectives: Biodegradable implants can be used in patients with bone fractures and make a second surgery to remove them unnecessary. In the last years bioresorbable Magnesium implants are under investigation due to the high biocompatibility and low stress shielding which means similar mechanical properties compared to the bone. However, Magnesium implants display high corrosion rates in in vivo experiments. High degradation rate can be minimized by 1) processing implants with different alloying elements and 2) by changing and modifying implants' surface.

In this study, 3 different Mg-based implants (Mg2Ag, Mg10Gd and pure Mg) were investigated and compared in their degradation behavior during bone healing process in tomography and histology level. The pure magnesium was used as a control. Mg2Ag was studied because of the promising antibacterial properties in in vitro studies. Gadolinium belongs to the rare earth elements and is known to increases the mechanical properties of Mg implants.

For these reasons, the aim of this study is to investigate the degradation behavior of these three different Mg-alloys during bone healing process in a growing rat model in the first 6 months.

Methods: Cylindrical pins (diameter 1.6 mm, length 8 mm) of Mg2Ag, Mg10Gd and pure Mg (99.9%) were implanted transcortically in growing male Sprague-Dawley rats in the femoral bone. MicroCT scans were performed 1, 4, 12 and 24 weeks post-operation (n=6/group). The implant surface, the implant volume and the gas formation were calculated using the software Mimics (Version: Mimics 15.0). Histological evaluation with Toluidine Blue has also proceeded.

Results: The Mg2Ag pins showed slow degradation, but first gas formation was obvious 1 week after implantation. After 4 and 12 weeks, the amount of gas gradually reduced and bone-implant surface contact regained. Compared to that, the Mg10Gd pins degraded fast and a high amount of gas formation interrupts bone healing and new bone formation around the implant. The pure Mg biodegradable implant showed also slow degradation and was well integrated into the bone until 24 weeks.

Conclusion: The Mg2Ag pins showed no adverse reactions in bone-implant contact. Generally, Mg2Ag processing has to be optimized because the early gas production 1 week after the implantation can be due to an inhomogeneous material. In comparison, the corrosion rate of Mg10Gd was faster and seems that the ion release cause disturbances in bone healing process. Furthermore, toxicological study for Gadolinium distribution in tissues must be taken under consideration.