Ultra-Liquid-Repellent Surfaces: from wetting to anti-biofouling properties

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Significant incidence of hospital-acquired infections due to fouling of biomedical devices, which are major public health threats contributing to prolonged hospital stay and death, has generated much attention over the past two decades. For example, indwelling urinary catheters are responsible for most hospital-acquired urinary tract infections (UTIs), which account for approximately 35-40% of all hospital-acquired infections. This is followed by surgical site infections that account for 20% of all hospital-acquired infections. The pathogenesis of these infections is related to the susceptibility of device/instrument surfaces to bacterial adhesion and microbial colonization. Under these circumstances, invasion of the bacteria to human bodies via medical devices such as surgical instruments and catheters (e.g., migrating along the urinary tract to the bladder and kidneys) is made utterly easy by the spreading and adhesion of liquids such as contaminated urine, blood and even water/moisture. However, due to insufficient attention to and understanding of wetting and adhesion of complex physiological fluids on the surfaces (both external and internal) of biomedical devices, there has been rather limited progress in preventing fouling-associated infections.This proposal aims to gain an in-depth understanding of wetting and adhesion for anti-biofouling surfaces relevant for biomedical devices. 'Wetting' refers to how a liquid deposited on a surface spreads out. The phenomena of wetting are governed by interfacial tension and surface structure. In the case of droplets of liquid on a non-wettable surface, the droplets can form a roughly spherical shape, exhibiting a contact angle approaching 180 degrees. This allows droplets that are in contact with a liquid repellent surface to slide/roll off easily and remove surface contamination. By contrast, droplets will spread spontaneously on fully wettable solid surfaces to form a thin film. Recent advances in wetting-based applications have demonstrated that surfaces with extreme liquid repellence have great potential to facilitate anti-biofouling properties. Design and application of surfaces with improved durability and anti-biofouling properties whereby wetting and adhesion behaviours can be manipulated will be demonstrated in this work. Firstly, we will use state-of-the-art fabrication techniques to prepare various liquid repellent surfaces. This will allow us to compare and optimise the liquid repellence of the fabricated surface patterns, and thereby, prevent the impalement of the liquid into the fabricated surface structure in order to avoid contamination and corrosion. Specifically, we will investigate the wetting and adhesion behaviours of complex liquids, including urine and blood, to facilitate the development of ultra-liquid-repellent surfaces. We will develop methods to test how the surface properties are affected by interactions with various liquids. Where applicable, we will assess the impact of surface defects before and after interactions with the contaminating liquids. This is to improve the inherent antifouling properties by reducing surface-associated biofilm growth resulting from surface defects. Understanding how liquid repellence varies is key to enabling researchers to design robust anti-biofouling surfaces that can be used on medical devices with internal surfaces (such as catheters and colostomy bags) and medical-grade metals against aggressive contamination and corrosion.