Controlling the colonization of materials by microorganisms is crucial in a wide range of industrial and clinical settings. Owing to continuous advances in polymer chemistry, polymer-based devices have become increasingly used to reduce chronic infection and medical device failure. However, the underlying mechanisms that govern the interactions of bacteria with material surfaces remain poorly understood.The material properties, which alter bacterial attachment, are intricately entangled and include chemistry, hydration, surface charges, topography and mechanical properties. In order to shed further light on the complex issue of cell-substrate adhesion and the impact on it by surface elasticity, we investigated the initial bacterial retention of <i>Escherichia Coli</i> on model poly(dimethysiloxane) (PDMS) surfaces.<br/>Our reference PDMS system was designed such that out of the three parameters, that determine bacterial retention (chemical composition, stiffness and surface topography), only one was systematically varied, i.e. the mechanical stiffness. Initial bacterial retention could thus be monitored depending on a single parameter, i.e. materials Young’s modulus. Substrates were engineered such that the surface modulus values, as measured by atomic force microscopy, ranged between 2 and 9 MPa. This was achieved by varying the crosslinking density of PDMS. Following crosslinking, we performed Soxhlet extraction to investigate the effect of non-crosslinked, free chains. The number of bacteria retained, as assessed by initial retention studies, decreases with the increase of both the bulk and surface mechanical stiffness values down to a value corresponding to the Young’s modulus of the bacterial cell. For higher values than this threshold, the number of adherent bacteria remains constant. We tentatively explain this observation by considering conformal overlay of bacterial and material surfaces, which might be addressed by considering elastocapillary effects and contact mechanics between bacteria and a soft elastomer surface.

Initial bacterial retention on polydimethylsiloxane of various stiffnesses; the relevance of modulus (mis)match

ACS Spring 2022

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