Microstructure, chemical and biological performance of boron-modified TiCaPCON films

The fabrication of biologically safe materials with enhanced antibacterial characteristics is of great significance. Here we propose B-based therapeutic strategy which offers a good alternative to the widely used approach based on the introduction of most famous bactericidal elements, such as Ag, Cu, and Zn. B-doped TiCaPCON films with 8, 11, and 15 at.% of B were obtained by simultaneous magnetron sputtering of two composite targets (TiC-CaO-Ti₃PO_x and TiB₂) in a gaseous mixture of Ar+15%N₂. The B content in the films was controlled by changing magnetron current of the TiB₂ target. The B-doped films were thoroughly studied by means of scanning and transmission electron microscopy, high-resolution TEM, X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and glow discharge optical emission spectroscopy. The films were also characterized with respect to surface wettability, boron ion release, and electrochemical characteristics. To test biocompatibility and bioactivity of the films in vitro, spreading, actin cytoskeleton organization, proliferation and osteogenic differentiation of MC3T3-E1 osteoblastic cells grown on the film surface were studied. The antibacterial characteristics of the B-doped TiCaPCON samples against antibiotic-resistant Escherichia coli (E. coli) 261 strains were compared with two-layer BO_x/TiCaPCON–B and TiO_x/TiCaPCON–B films obtained by three different methods: (i) deposition of a B₂O₃ top layer, (ii) annealing and (iii) electrochemical oxidation of the as-deposited B-doped films. The obtained results clearly indicated that all types of B-containing films are not toxic for cells regardless of their surface composition. Antibacterial activity tests revealed that only the sample with B₂O₃ top layer completely inactivated E. coli cells and prevented biofilm formation. Thus the surface of two-layer B₂O₃/TiCaPCON–11%B film was simultaneously bactericidal towards E. coli strains and not-toxic for osteoblastic cells.