Multi-modal investigation of the bone micro- and ultrastructure, and elemental distribution in the presence of Mg-xGd screws at mid-term healing stages

Magnesium(Mg)–based alloys are becoming attractive materials for medical applications as temporary bone implants for support of fracture healing,e.g.as a suture anchor.Due to their mechanical properties and biocompatibility,they may replace titanium or stainless-steel implants,commonly used in orthopedic field.Nevertheless,patient safety has to be assured by finding a long-term balance between metal degradation,osseointegration,bone ultrastructure adaptation and element distribution in organs.In order to determine the implant behavior and its influence on bone and tissues,we investigated two Mg alloys with gadolinium contents of 5 and 10 wt percent in comparison to permanent materials titanium and polyether ether ketone.The implants were present in rat tibia for 10,20 and 32 weeks before sacrifice of the animal.Synchrotron radiation-based micro computed tomography enables the distinction of features like residual metal,degradation layer and bone structure.Additionally,X-ray diffraction and X-ray fluorescence yield information on parameters describing the bone ultrastructure and elemental composition at the bone-to-implant interface.Finally,with element specific mass spectrometry,the elements and their accumulation in the main organs and tissues are traced.The results show that Mg-xGd implants degrade in vivo under the formation of a stable degradation layer with bone remodeling similar to that of Ti after 10 weeks.No accumulation of Mg and Gd was observed in selected organs,except for the interfacial bone after 8 months of healing.Thus,we confirm that Mg-5Gd and Mg-10Gd are suitable material choices for bone implants.

Multiscale morphological analysis of bone microarchitecture around Mg-10Gd implants

The utilization of biodegradable magnesium(Mg)-based implants for restoration of bone function following trauma represents a transformative approach in orthopaedic application.One such alloy,magnesium-10 weight percent gadolinium(Mg-10Gd),has been specifically developed to address the rapid degradation of Mg while enhancing its mechanical properties to promote bone healing.Previous studies have demonstrated that Mg-10Gd exhibits favorable osseointegration;however,it exhibits distinct ultrastructural adaptation in comparison to conventional implants like titanium(Ti).A crucial aspect that remains unexplored is the impact of Mg-10Gd degradation on the bone microarchitecture.To address this,we employed hierarchical three-dimensional imaging using synchrotron radiation in conjunction with image-based finite element modelling.By using the methods outlined,the vascular porosity,lacunar porosity and the lacunar-canaliculi network(LCN)morphology of bone around Mg-10Gd in comparison to Ti in a rat model from 4 weeks to 20 weeks post-implantation was investigated.Our investigation revealed that within our observation period,the degradation of Mg-10Gd implants was associated with significantly lower(p<0.05)lacunar density in the surrounding bone,compared to Ti.Remarkably,the LCN morphology and the fluid flow analysis did not significantly differ for both implant types.In summary,a more pronounced lower lacunae distribution rather than their morphological changes was detected in the surrounding bone upon the degradation of Mg-10Gd implants.This implies potential disparities in bone remodelling rates when compared to Ti implants.Our findings shed light on the intricate relationship between Mg-10Gd degradation and bone microarchitecture,contributing to a deeper understanding of the implications for successful osseointegration.