Microfluidic disturbances on synthetic patterned surfaces and their impact on microorganisms in relation to biofouling control

Abstract

Biofouling, the unwanted growth of sessile microorganisms on submerged surfaces, presents a serious problem for underwater structures, water vessels and medical devices. It is ubiquitous in nature and readily develops on any unprotected surfaces in both the marine and physiological environments. Conventionally the underwater structures and water vessels are being protected against biofouling by metal based antifouling paints. The use of antifouling paints, in particular those containing Copper and Tributyltin (TBT), have been extremely successful for the hulls of ships by killing the majority of fouling species. Similarly, antibacterial medical coatings containing silver or antibiotics are being used frequently. These coatings have many detrimental effects including the mutation of bacteria which enables antibiotic-resistant biofilm development, failure of medical devices such as hip and knee implants, cause of catheter-associated urinary tract infection (CAUTI) and other hospital-acquired infections. The use of biocide-based metallic paints in the ocean and the silver-based antibacterial medical coating are posing more ecological and toxicity concerns and thus led to a mounting interest in developing non-toxic and no-kill alternatives for these systems. One of the non-toxic approaches to control biofouling is to modify the settlement surface. This usually entails altering the surface topography and roughness, and developing a surface with a microstructured pattern. Studies showed that patterned surfaces inhibit the initial settlement of microorganisms and prolong the subsequent biofilm formation process. Though it is well documented that biofouling can be controlled to various degrees with different microstructure-based patterned surfaces, the understanding of the underlying mechanism is still imprecise. The present study considered that microtopographies might influence near-surface microfluidic conditions, thus microhydrodynamically preventing the settlement of microorganisms. It is therefore aimed to characterize the microfluidic environment developed on patterned surfaces and its relation with the antifouling behaviour of those surfaces. In this study, patterned surfaces with microwell arrays were assessed experimentally with a real-time biofilm development monitoring system using a novel microchannel-based flow cell reactor. The dynamic interaction of a motile bacterium ( Escherichia coli ) with microtopographies was investigated by observing and assessing the trajectories of individual cells across an array of microwells using a time-lapse imaging module and image processing software. The effects of the solid boundaries on the dynamic stability of E. coli cells were assessed numerically using computational fluid dynamics (CFD) simulations. From this study, it is evident that patterned surfaces develop fluctuating stress-strain rates around microorganisms, alter their swimming depths, make them dynamically unstable and thus exhibit antifouling characteristics in a submerged condition. It is also stated that microstructures, capable of developing high wall shear bounded zones, keeping microorganisms away from the base surface, and giving no shelter against fluctuating microfluidic forces, could be considered effective in biofouling control. Finally, this study suggested a few optimized design patterns of microstructure-based antifouling surfaces, to develop effective microfluidic conditions capable of inhibiting the initial settlement of microorganisms