The mineralization of the collagenous matrix in bone is among the most important factors governing bone growth and quality. Here, a novel class of biodegradable Mg alloy has been used to provide structural support after bone fracture. After sufficient time the implants gradually degrade and by that a second operation to remove the implant can be avoided. This is especially important when fracture healing and bone growth are overlapping, such as it is in the case of e.g. children.
The response of bone mineralization upon a degradable Mg implant was monitored in a rat model (Sprague-Dawley rat, two weeks old) over a growth period from 1 to 18 months. Alterations in the bone nano- and mineral structure were investigated by means of synchrotron-based methods such as small-angle x-ray scattering (SAXS) and diffraction (XRD) , x-ray fluorescence (XRF), as well as x-ray absorption spectroscopy (XAS) at a spatial resolution of about 3 µm.
The combined investigations unveiled not only nanostructural changes such as altered mineral crystal size in response to the implant degradation but also impact on the bone mineral structure by the presence of Mg ions from the implant. The implant-bone interface shows Mg enrichment in the context of new bone formation, indicating that Mg is predominantly incorporated into the bone mineral by bone remodeling. Interestingly, increased concentrations of Mg were also observed in the vicinity of blood vessels several hundreds of µm away from the bone-implant interface from the earliest points in time. This may indicate that resorbed Mg was re-deposited into the bone matrix via the blood-vessel pore network of the bone
The electronic state of the bone constituents phosphorus and magnesium was investigated by means of synchrotron x-ray absorption near - and extended edge spectroscopy. A gradual substitution of Ca by Mg in the crystal lattice could be observed at bone regions adjacent to the implant as well as around blood vessels, underlining the impact of Mg on the local bone HAP structure and its influence during the bone formation.
Our study therefore helps towards understanding the degradation kinetics of Mg implants and potentially allows for optimizing custom-tailored implants meeting the patient’s specific needs.