Antibacterial Properties of Ag-modified Ca-Phosphate Scaffolds for Bone Implant Applications

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In a previous phase of our research program, vapor transport sintering was successfully applied to calcium phosphate (CaP) ceramics, establishing an innovative method for the fabrication of bioactive implant materials with interconnected porosity. Among the most important results was the combination of nearly shrinkage-free sintering of the ceramic scaffolds and a surface modification with silver particles in one processing step, potentially lending antibacterial properties to the material. However, vapor phase transport has its limitations, since it produces too small pore diameters for bone tissue ingrowth. Therefore, in order to complete this study, we propose (i) the application of vapor transport sintering in AgCl atmosphere to macroporous CaP scaffolds with sufficiently large pore diameters and (ii) in-vitro testing to assess the antibacterial properties of these novel composite materials.(i) Ag-modification of biogenic calcium phosphate scaffolds via vapor transport sinteringHydrothermally converted biogenic carbonates will be used as scaffold materials (HA: hydroxyapatite, and BCP: biphasic calcium phosphate) to be modified with Ag particles, as they provide the pore volume and interconnected pore geometry required for bone graft applications. Whereas the conversion of coralline aragonite to HA is a commercially established process, our previous experiments with sea urchin spines have shown great potential for the fabrication of BCP composites that offer superior bioresorbability, as compared to pure HA. Loading the scaffold's surface with finely dispersed metallic Ag particles is a novel process that is expected to lend antibacterial properties to the ceramic implant.(ii) In-vitro assessment of antibacterial propertiesConcerning the potential application of Ag-modified ceramic scaffolds as a bone implant material, it is of particular interest if silver ions are dissolved at an appropriate rate to unfold their antibacterial properties. Therefore, solubility tests under simulated physiological conditions will be performed. Positive results provided, we will proceed with cell culture experiments using bacterial strains typically found on the skin and in chronically infected wounds.