Synthesis, processing and in vivo degradation behaviour of magnesium phosphate minerals for bone replacement

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Magnesium phosphate minerals are relatively new within the field of bone replacement materials, whereby the knowledge about most of those compounds is limited regarding their degradation and bone regeneration capacity at orthotopic implantation sites. In addition, there is a lack of processing regimes to transfer most of the minerals into clinically applicable forms (e.g. cements, granules, solid bodies). The project aims to fill this gap by firstly evaluating diverse process techniques for the synthesis of different magnesium phosphate minerals such as struvite, K-struvite, bobierrite, dittmarite or cattiite with defined particles sizes and phase composition. Both the solubility product and rate of dissolution of those compounds under physiological conditions, as well as changes of their phase composition when in contact with the extracellular liquid, are of crucial interest. In the second part, the minerals will be transferred into suitable application forms for bone replacement, including granules and cement pastes. The latter will form the aforementioned minerals depending on cement paste stoichiometry and pH value. The materials will be thoroughly characterized inclusive of the osteoclast-mediated resorption, whereby the active cellular resorption will be determined from released Mg2+ and phosphate ions. Based on these results, the last part of the project comprises the investigation of four different materials in form of cement pastes and granules in a sheep model in vivo. Here, granules will be implanted into a drill hole defect into the femoral condyle and the cement pastes will be investigated in a partial load-bearing proximal tibial defect. After 2 and 4 months, the animals will be sacrificed to assess the quality of the regenerated bone histologically and biomechanically. The material degradation will be analysed and quantified by XRD and the incorporation of magnesium ions into the newly formed bone will be determined by EDX analysis.