Impact of Chemical Heterogeneities of Surfaces on Colonization by Bacteria.

An essential yet never addressed parameter for the control of bacteria on functionalized biomaterial is surely the accessibility and heterogeneity of the functional groups immobilized on the surface. In this context, we investigated the colonization (Escherichia coli K12, Staphylococcus epidermidis RP62A) of precisely engineered surfaces revealing various densities of NH2 and CH3 functional groups. We demonstrated for the first time nonlinear relationships between the NH2/CH3 surface fraction and the quantity of adhered, adhering or detaching bacteria. Plateaus and transition zones were related to the range of NH2/CH3 surface fraction offering stability or sharp variation in bacterium/surface interactions. The nonlinear behavior was attributed to the discrete distribution of positive charges revealed by the bacterial membrane in the continuum of negative charges resulting from the phospholipids, which may correlate with one single specific distribution of positive NH3+ charges on the material surface, because of electrostatic, repulsive interactions occurring at the local, molecular scale.

Self-assembled molecular platforms for bacteria/material biointerface studies: importance to control functional group accessibility.

Highly controlled mixed molecular layers are crucial to study the role of material surface chemistry in biointerfaces, such as bacteria and subsequent biofilms interacting with biomaterials. Silanes with non-nucleophilic functional groups are promising to form self-assembled monolayers (SAMs) due to their low sensitivity to side-reactions. Nevertheless, the real control of surface chemistry, layer structure, and organization has not been determined. Here, we report a comprehensive synthesis and analysis of undecyltrichlorosilane- and 11-bromoundecyltrichlorosilane-based mixed SAMs on silicon substrates. The impact of the experimental conditions on the control of surface chemistry, layer structure, and organization was investigated by combining survey and high-resolution X-ray photoelectron spectroscopy analysis, wettability measurements, and ellipsometry. The most appropriate conditions were first determined for elaborating highly reproducible, but easily made, pure 11-bromoundecyltrichlorosilane SAMs. We have demonstrated that the control is maintained on more complex surfaces, i.e., surfaces revealing various chemical densities, which were obtained with different ratios of undecyltrichlorosilane and 11-bromoundecyltrichlorosilane. The control is also maintained after bromine to amine group conversion via SN2 bromine-to-azide reactions. The appropriateness of such highly controlled amino- and methyl-group revealing platforms (NH2-X%/CH3) for biointerface studies was shown by the higher reproducibility of bacterial adhesion on NH2-100%/CH3 SAMs compared to bacterial adhesion on molecular layers of overall similar surface chemistry but less control at the molecular scale.