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

The TiO₂ nanotube pattern with features down to 20 nm (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 80 nm 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.