Interactions of bacteria with specific biomaterial surface chemistries under flow conditions

The effect of specific chemical functionalities on the adhesion of two Staphylococcus epidermidis strains under flow was investigated by using surfaces prepared by self-assembly of alkyl silane monolayers on glass. Terminal methyl (CH3) and amino (NH2) groups were formed in solution and by chemical vapor deposition of silanes, at elevated temperature. Hydroxyl (OH)-terminated glass was used as control. Surface modification was verified by contact angle and zeta potential measurements, atomic force microscopy and X-ray photoelectron spectroscopy. A parallel plate flow chamber was used to evaluate bacterial adhesion at various shear rates. The effect of the solution’s ionic strength on adhesion was also studied. Adhesion was found to be dependent on the monolayer’s terminal functionality. It was higher on the CH3 followed by the NH2 and minimal on the OH-terminated glass for both strains. The increase in the ionic strength significantly enhanced adhesion to the various substrates, in accordance with the Derjaguin–Landau–Verwey–Overbeek (DLVO) theory. The extended DLVO theory explained well the combined effects of surface and solution properties on bacterial adhesion under low shear rates. However, the increase in the shear rate restricted the predictability of the theory and revealed macromolecular interactions between bacteria and NH2-terminated surfaces.