Development and industrial upscaling of composite coatings containing silver with antimicrobial properties

Bacterial and viral infection transmission is a significant global challenge. The application of antibacterial and antiviral coatings on surfaces is a promising approach to reduce contamination and spread of harmful pathogens. In this context, silver nanoparticles (AgNPs) are an effective agent to provide antibacterial properties to materials in multiple application fields, thanks to their high surface-to-volume ratio and small size. These characteristics enable AgNPs to interact more effectively with bacterial cells, disrupting them and allowing easy penetration through biological barriers. Among the application fields, AgNPs could be potentially appropriate to produce antibacterial textiles, hospital protective clothing that prevent bacterial contamination and antibacterial air filters to purify air and reduce the presence of pathogenic bacteria. The aim of this thesis focused on the development and characterization of an antibacterial composite coating. It was deposited via co-sputtering on cotton fabrics and HEPA H14 filters in the laboratories of the Glance Group of Politecnico di Torino. The coating is composed of a matrix of silica (SiO2) and zirconia (ZrO2) incorporating silver (Ag) in the form of nanoclusters. The coated samples underwent compositional, morphological and structural characterization through Energy Dispersive X-ray Spectroscopy (EDS), Field Emission Scanning Electron Microscopy (FESEM), Ultraviolet-Visible Spectroscopy (UV-Vis Spectroscopy) and X-ray Diffractometry (XRD). The antibacterial efficacy of the coating was assessed using the inhibition halo test, the colony forming units (CFU) count test and a surface contamination test against the bacteria Staphylococcus epidermidis and Escherichia coli, which are Gram-positive and Gram-negative bacteria, respectively. Results indicated that the coating was characterized by an amorphous SiO2-ZrO2 matrix with embedded silver nanoclusters. Furthermore, the ion release test confirmed the effective release of silver ions with antibacterial properties, while washing resistance test revealed good durability and stability of the coating. Antibacterial tests suggested a high antibacterial efficacy against both bacterial strains. Moreover, an upscaling of the coating deposition process was started in collaboration with AGC Interpane within the EU funded project NANOBLOC. The aim is the technology transfer of the coating from lab to industrial scale. For this purpose, the company provided several larger coated fabrics, deposited through co-sputtering to replicate the lab scale coating. In order to control the success of the upscaling, several preliminary tests have been carried out. In particular, the evaluation of the composition of the coatings, as well as the antibacterial efficacy through the inhibition halo test and the resistance to washing cycles have been performed. In the future, the industrialization of these coatings could overcome the problem of bacterial contamination.