A continuous method to prepare poorly crystalline silver-doped calcium phosphate ceramics with antibacterial properties

Silver-doped calcium phosphate ceramics were prepared in discontinuous and continuous processes with different amounts of incorporated silver (up to 1.8 wt% silver). In particular, the effects of pH, reaction time and light exposure on the incorporation of silver into the calcium phosphate ceramic were investigated. In the dark, silver can be incorporated as colourless silver ions (Ag+) into the apatite lattice, but the integration occurs slowly. Under ambient light, a rapid photoreduction to elemental silver (Ag-0) occurs which permits a continuous process to prepare silver-doped calcium phosphate ceramics. The silver-doped calcium phosphate ceramics were characterized by scanning electron microscopy, X-ray powder diffraction, infrared spectroscopy, thermogravimetry, and elemental analysis (Ca, Ag, phosphate). The silver release from the silver-doped calcium phosphate ceramics was measured by a combination of dialysis and atomic absorption spectroscopy. The antimicrobial effect was tested on bacteria (Escherichia coli), and the cytotoxic effect was tested on HeLa cells (human epithelial cervical cancer cells). For comparison, stoichiometric silver phosphate, Ag3PO4, was prepared. The release of silver from silver phosphate is much faster, leading to pronounced antibacterial but also cytotoxic effects.