Versatile Nanocomposite Coatings with Tunable Cell Adhesion and Bactericidity

TiO2-Ag nanocomposites are known for their bactericidal effect during exposure to appropriate UV radiation. While involving hazardous radiation, and limited to accessible areas, the bactericidity of these coatings is not persistent in the absence of UV light, which impedes their commercial application. Herein it is shown that TiO2-Ag nanocomposites can be made highly bactericidal without the need of irradiation. Beyond this, bactericidity can even be mitigated in the presence of pre-irradiated coatings. Biocompatibility and cell adhesion are also negligibly small for the as-processed, non-irradiated coatings, and become fairly high when the coatings are irradiated prior to testing. This opens the possibility to pattern the coatings into areas with high and low cell adhesion properties. Indeed by irradiating the coating through a mechanical mask it is shown that fibroblast cell adherence is sharply confined to the irradiated area. These properties are achieved using TiO2-Ag thin films with high silver loadings of 50 wt%. The films are processed on stainless steel substrates using solution deposition. Microstructural characterization by means of X-ray diffraction, Raman, and X-ray photoelectron spectroscopy, high-resolution scanning electron microscopy, and atomic force microscopy show a highly amorphous TiO2-AgxO nanocomposite matrix with scattered silver nanoparticles. UV irradiation of the films results in the precipitation of a high density of silver nanoparticles at the film surface. Bactericidal properties of the films are tested on a-haemolyzing streptococci and in-vitro biocompatibility is assessed on primary human fibroblast cultures. The results mentioned above as to the tunable bactericidity and biocompatibility of the TiO2-Ag coatings developed herein, are amenable to silver ion release, to catalytic effects of silver nanoparticles, and to specific wettabilities of the surfaces.