Studying the influence of surface properties on the cell attachment and anti-fouling capacity of Ag/SiO2 superhydrophobic coatings for building materials

Anti-fouling coatings are a common solution for the protection of porous building materials from the effects of microbial colonization over their functionality and durability. Usually, this is achieved through the incorporation of biocides or the passive control by reducing bioreceptivity. Superhydrophobic surfaces are considered a promising strategy due to their reported capacity for reducing cell adhesion, but their affinity to non-polar substances may decrease their effectiveness under the right circumstances (e.g. organic contamination, cell walls with hydrophobic domains). The combination of these surfaces with active biocides may compensate these drawbacks, however, a close contact with the microorganisms is necessary to promote their effect. This work studies the factors that determine the anti-fouling capacity of a coating, tested on porous building materials, that combines superhydrophobic surface with a nanostructured Ag/SiO2 biocide agent. Special attention is paid to understanding to which extent the cell-surface interactions modulate the initial cell attachment to the surface and the biocidal effect. To this end, the electrostatic forces and surface energy balance were considered using different reference bacteria and a yeast. The results indicate that the hydrophobic character of the surface favors the cell attachment and the biocide agent may be unable to fully compensate this effect for all microorganisms. In addition, changes in micro and nano roughness seem to play an equally significant role. Overall, this study aims to provide a theoretical and experimental insight to assist in the future design of anti-fouling coatings tailored to the organisms responsible of fouling processes.