Characterising the Antimicrobial Performance of Engineered Layered Double Hydroxide Surfaces for Biofilm Control

Antimicrobial resistance (AMR) is a growing global health concern driven by bacterial biofilm formation, which increases tolerance to treatments. Developing surface-based strategies to limit biofilm formation is therefore critical. Layered Double Hydroxides (LDHs) are 2D brucite-like nanomaterials with tuneable physicochemical properties that may reduce bacterial colonisation. Their ease of synthesis, with scalability potential for industrial production, alongside their characteristic and tunable physicochemical properties, makes them a promising nanostructured coating for antimicrobial applications. This study evaluates LDH thin-film coatings as intrinsic antimicrobial surfaces, focusing on the combined effects of chemical composition, nanotopography, and wettability on biofilm formation in Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa. Four aluminium-based LDHs (ZnAl-NO₃, ZnAl-Cl₂, MgAl-NO₃, MgAl-Cl₂) were synthesised via coprecipitation or in situ growth on aluminium substrates. Materials were characterised by XRD, SEM, EDS, and contact angle measurements. Antimicrobial performance was assessed by quantifying colony-forming units (CFU mL^-1) after bacterial exposure. ZnAl-LDH surfaces showed significant antimicrobial activity against E. coli and S. aureus, while MgAl-LDHs showed no effect and occasionally increased bacterial growth. None of the LDH surfaces tested exhibited significant antimicrobial activity against P. aeruginosa strain. The antimicrobial performance of ZnAl-LDH can be attributed to the concurrent effect of the surface chemistry, wettability, and sharp platelet-like nanotopography. The results obtained demonstrate that ZnAl-LDH-based coatings are promising antimicrobial materials with potential relevance for translational research in clinical antimicrobial surface development.