Modification of silica surface with nonstoichiometric calcium phosphate and its effects on protein adsorption and osteoblast response

Surface modification of silica particle by calcium phosphate (CaP) film using a heterogeneous precipitation method is reported in this study. Surface potential of silica particle was actively changing at 50 min of soaking at 37 °C. The surface morphological change observed using field emission scanning electron microscopy (FE-SEM) revealed the highly porous structure of the film and formation pattern was well agreed with that of zeta potential. Fourier transform infrared spectroscopy (FTIR) was used to evaluate the chemical composition of the surface of the CaP film. Chemical composition acquired from energy dispersive X-ray spectroscopy (EDX) illustrated that the CaP films consist of calcium and phosphorus and provided the atomic molar ratio of calcium and phosphorus indicating that the CaP films are non-stoichiometric apatites. The specific surface area of the silica particles was increased by ~ 2.5-fold when the CaP film was formed on the silica particles. Protein adsorption assays demonstrated that the CaP film had a significant effect on interaction with protein characterized in terms of adsorbed mass and surface charge. The adsorption of model proteins, albumin and lysozyme, was reduced in the presence of CaP film. Lysozyme adsorption appeared to be governed by electrostatic attraction, whereas albumin caused gradual decrease in the negativity of surface potential with increase of lysozyme solution concentration. Cell viability assays using human osteoblast MG63 cells confirmed that the film is cytocompatible. This study strengthened our understanding of interaction between protein and CaP and can be applied to surface modification of bone substitutes in granular shapes for the promotion of bone regeneration.