Preparation and antibacterial activity of hybrid materials containing quaternary ammonium salts via sol–gel process

Organic–inorganic hybrid coatings containing quaternary ammonium salts (QAS) bonded to the organic–inorganic network were prepared from tetraethoxysilane and triethoxysilane terminated poly(ethylene glycol)-block-poly(ethylene) using a sol–gel process. They were applied as a thin layer (0.6–1 μm) to PE films and the antibacterial activity of the coated films was tested against both Gram-negative ( Escherichia coli ATCC 25922) and Gram-positive ( Staphylococcus aureus ATCC 6538) bacteria. Measurements at different contact times showed a rapid decrease of the viable count for both the tested strains. In particular, after 48 h of contact, a decrease of 96.4% and 99.1% of E. coli and S. aureus, respectively, was observed. The permanence of the antibacterial activity of the coated films was demonstrated through repeated washings and prolonged immersion in physiological saline solutions at 37 °C. Indeed, due to the removal of QAS moieties by the nucleophilic attack of water, the antibacterial activity after 24 h was strongly reduced when measured on samples submitted to several washings. However, a quite good antibacterial activity was observed even on the same samples after 96 h, probably due to a spontaneous partial restoring of the QAS on the surface. Very good transparency, quite good adhesion and high wettability are further features of these hybrid coatings.