Maria G. Katsikogianni

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 (CH(3)) and amino (NH(2)) 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 solutions ionic strength on adhesion was also studied. Adhesion was found to be dependent on the monolayers terminal functionality. It was higher on the CH(3) followed by the NH(2) 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 NH(2)-terminated surfaces.

Staphylococcus epidermidis adhesion to He, He/O2 plasma treated PET films and aged materials: Contributions of surface free energy and shear rate

Adhesion studies of bacteria (Staphylococcus epidermidis) to plasma modified PET films were conducted in order to determine the role of the surface free energy under static and dynamic conditions. In particular, we investigated the effect of the ageing time on the physicochemical surface properties of helium (He) and 20% of oxygen in helium (He/O(2)) plasma treated polyethylene terephthalate (PET) as well as on the bacterial adhesion. Treatment conditions especially known to result in ageing sensitive hydrophilicity (hydrophobic recovery) were intentionally chosen in an effort to obtain the widest possible range of surface energy specimens and also to avoid strong changes in the morphological properties of the surface. Both plasma treatments are shown to significantly reduce bacterial adhesion in comparison to the untreated PET. However, the ageing effect and the subsequent decrease in the surface free energy of the substratum surfaces with time - especially in the case of He treated samples - seem to favor bacterial adhesion and aggregation. The dispersion-polar and the Lifshitz-van der Waals (LW) acid-base (AB) thermodynamic approaches were applied to calculate the Gibbs free energy changes of adhesion (DeltaG(adh)) of S. epidermidis interacting with the substrates. There was a strong correlation between the thermodynamic predictions and the measured values of bacterial adhesion, when adhesion was performed under static conditions. By decoupling the (DeltaG(adh)) values into their components, we observed that polar/acid-base interactions dominated the interactions of bacteria with the substrates in aqueous media. However, under flow conditions, the increase in the shear rate restricted the predictability of the thermodynamic models.

Bacterial adhesion onto materials with specific surface chemistries under flow conditions

Staphylococcus epidermidis adhesion onto materials with specific chemical functionalities, 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 by chemical vapor deposition of silanes, at elevated temperature. Carboxyl (COOH) terminated groups were prepared by further modification of NH2 groups with succide anhydride and positively charged NH2 groups by adsorption of poly-l-lysine hydrobromide. Hydroxyl (OH) terminated glass was used as control. Surface modification was verified by contact angle measurements, atomic force microscopy and X-ray photoelectron spectroscopy. A parallel plate flow chamber was used to evaluate bacterial adhesion at various shear rates. Adhesion was found to be depended on the monolayer’s terminal functionality. It was higher on the CH3 followed by the positively charged NH2, the non-charged NH2 groups, the COOH and minimal on the OH-terminated glass. The increase in the material surface free energy significantly reduced the adhesion of a hydrophilic bacterial strain, and this is in accordance with the predictions of the thermodynamic theory. However, the increase in the shear rate restricted the predictability of the theory and revealed macromolecular interactions between bacteria and NH2- and COOH-terminated surfaces.

Use of atmospheric plasma jet treatments for the enhancement of cell adhesion to 1 mm internal diameter microwell cell arrays

In this study a cyclic olefin copolymer (COC) is micro-injection moulded to manufacture miniature multiwell plates with biodiagnostic applications. The biological inertness of the COC polymer however hampers the cell growth. In order to address this problem, the feasibility of using both helium and air atmospheric plasma treatments for the activation of the well arrays was investigated. In addition to evaluating if the enhancement in the polymer surface energy would facilitate cell attachment onto the internal surface of the wells, a further issue was to avoid thermal damage by the plasma to the 1 mm internal diameter microwell cell arrays.