Adhesion and friction forces in biofouling attachments to nanotube- and PEG- patterned TiO2 surfaces.

The TiO2 nanotube pattern with features down to 20nm (TN20) is highly and efficiently resistant to fibrinogen and S. aureus attachment. The ability of TN20 to resist biofouling adsorption, is due to low biofouling-surface adhesion force that determines the initial biofouling attachment, as well as the low friction coefficient that enables a complete removal of biofouling from a low-adhesive 'repelling' TN20 substrate under fluid flow. By grafting PEG molecules onto TN20, a significantly higher S. aureus cells attachment was observed, because of the stronger adhesion forces originated from the deformation of the soft PEG coatings. The complete interaction of S. aureus on structure-free dense TiO2 (DT), yields larger contact area and thus higher adhesion force than on any other TiO2 surfaces, resulting in a high coverage of bacteria. The existing high friction coefficient of S. aureus on TN80 (TiO2 with 80nm nanotubular size) and TN80-P (PEG-modified TN80), due to the much greater surface roughness, would contribute to the immobilization of biofouling on the surface under fluid flow, even though the two surfaces exhibit low adhesion forces. The analysis of adhesion and friction forces manipulated by TiO2 nanotubular topography and posted PEG patterns, advances our understanding of the mechanisms by which nanotopography patterned surfaces reduce biofouling attachment.