Physicochemical characterization and cell behavior of porous hydroxyapatite ceramics doped with Ag ions: Fluorescence quenching in fluorescence-labeled cells

Mouse preosteoblast cells were found to adhere well to and spread on the surface of porous Ag-doped hydroxyapatite (HAp) ceramics fabricated using a small amount of Ag. Ag particles were deposited on the surfaces of the HAp ceramics fabricated by doping Ag in large amounts. These Ag-doped samples were more hydrophobic owing to the loss of OH ions from HAp lattices with increasing the amount of added Ag. The cells adhered to the hydrophobic surface even in the presence of cytotoxic Ag particles. Consequently, the equilibrium between the hydrophobicity of the surface and cytotoxicity of Ag particles determines cell adhesion. Additionally, fluorescence quenching did not occur in cells stained for nuclei (blue) and fibronectin (red), but in cells stained for actin (red and green), in the presence of Ag particles. Charge transfer from actin protein molecules to Ag particles enabled quenching because the Ag particles exerted the heavy-atom effect.