(245d) Nanotopographical Amplification of Bacteria-Material Repulsive Interactions for Mitigating Bacterial Attachment and Biofilm Formation

Pathogenic biofilms persisting on abiotic surfaces have wreaked havoc in healthcare and food safety. Numerous practical experiences and researches have made evident that the eradication of mature bacterial biofilms is extremely difficult with the conventional removal and disinfection methods, including the use of antibiotics. Recently, preventative strategies targeting the most vulnerable step of the biofilm life cycle – i.e. the reversible attachment of planktonic cells to abiotic surfaces – have shown particular promise. Here we present a novel nanotopography-enabled strategy, which leverages the repulsive cell-substrate interaction forces, to inhibit bacterial attachment and biofilm formation.

To this end, anodized aluminum oxide (AAO) substrates with defined pore diameters (10nm, 25nm, 50nm, and 100nm) and a smooth control, were incubated statically for 48h with pure cultures of Escherichia coli, Listeria monocytogenes, Staphylococcus aureus, and Staphylococcus epidermidis. Surface properties (surface charge and surface energy) and morphology (or topography) of the test strains and the AAO substrates were characterized using contact angles, zeta potential measurements, SEM, and AFM. These results were used as inputs for predicting the cell–substrate interaction forces, based on the extended Derjaguin–Landau–Verwey–Overbeek (XDLVO) theory. The force predictions were correlated with the surface-bound biomass (quantified by confocal laser scanning microscopy) for all strain-topography pairs, to evaluate the predictive power of the XDLVO model. Furthermore, force-distance curves were collected using functionalized AFM colloidal probes to directly verify the nanotopography dependency of the repulsive forces.

AAOs with pore diameters of 15nm and 25nm were able to effectively reduce bacterial attachment and biofilm formation by all strains compared to the smooth control; however, 50nm- and 100nm-pore AAOs resulted in more biomass accumulation. Logarithmic biomass was found negative correlated with the maximum repulsive forces (F_max) predicated by the XDLVO model (r = 0.79). The main contributors to F_max were the surface-originated electrostatic and acid-base interactions, which were substantially enhanced by the immense vertical surface area characteristic of the 15nm- and 25nm-pore AAOs. Furthermore, AFM force-distance measurements suggested that cellular appendages and the membrane bound polymeric molecules also played an important role in the nanotopography dependency of the reversible attachment.

These findings elucidated the nanotopography dependency of bacterial attachment and biofilm formation, which in turn serves as a roadmap toward more effective bacteria-repellent nanotopographies for mitigating pathogenic biofilms.