Silver-functionalized methyl-silica hybrid materials as antibacterial coatings on surgical-grade stainless steel

In this work, the development of an antibacterial coating for metallic substrates is presented. The coating consists in a hybrid organic-inorganic sol-gel material doped with silver. The relation between the structure of the hybrid matrix, aggregation state of silver ions, and biocide behavior is analyzed as a function of the densifying thermal treatment. Sol-gel materials were synthesized through hydrolytic condensation, in acidic conditions, of tetraethoxysilane (TEOS) and methyl-triethoxysilane (MTES). Silica nanoparticles were added in order to give a mechanical reinforcement and silver nitrate as the supplier of Ag+ ions. Coatings were deposited on 316L stainless steel and microscope glass slides by the dip-coating process at a constant withdrawal rate and densified at 50, 150 and 450 °C. X-ray photoelectron spectroscopy, small angle X-ray spectroscopy and electrochemical impedance spectroscopy were used as characterization techniques in order to elucidate silver aggregation and its influence on the structural evolution of the hybrid matrix, as a function of the thermal treatment. At the same time, the biocide behavior, as a function of silver state, particles size and thermal treatment, was studied by inhibitory halo identification on Escherichia-coli cultures in agar diffusion tests.