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

Abstract

Development of new materials enriched with noble metal ions, such as silver, cobalt or copper, is of great interest in the field of commercial and medical products due to its action against fungus and bacteria. Although a large number of products are chemically active against microorganisms, they are usually limited to fabrics for medical bandages and sportswear in order to avoid, respectively, infections and odors. On the other hand, sol-gel technology becomes the preparation of hybrid materials possible with introduction of different components, as inorganic salts or organic additives within its structure bringing up the possibility to develop functional materials for different purposes.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.