Antibacterial and Antifungal Action of Surfaces and Coatings are Dependent on the Surrounding Environmental Conditions and Deposition Mechanics

Many antimicrobial surfaces and coatings are capable of passing standardised test methods and so are being labelled as antimicrobial but are ineffective at point of use. Current common standardised test methods (e.g. ISO22196) specify environmental conditions unlikely to be found in an end-use scenario, particularly relative humidity that is kept artificially high (>90 %). This allows the inoculum to remain wet on the surface and allows moisture-dependent surfaces to remain active for the duration of the testing period. As standardised testing methods become more in-line with realistic conditions, knowledge of the impacts of different environmental conditions on moisture-dependent surfaces will become vital for informing on antimicrobial surface and coating directed placement. Additionally, the mechanisms surrounding the bacterial and fungal deposition in an evaporating droplet has implications for antimicrobial surface efficacy via conditioning films and the coffee ring effect.