Wetting Dynamics on Biological Surfaces

Abstract

Several interesting wetting phenomena occur on biological surfaces, e.g., super hydrophobic behavior of rough surfaces covered with wax crystals, collection of drinking water from fogladen wind through a condensation process, and surface tension-induced transport of prey in millimetric water droplets. Interfacial phenomena on hydrophilic rough surfaces coated with mucus such as the tongue and small intestine wall contribute to effective nutritional absorption or sensitization of the senses. However, there are few reports on the wetting phenomena on such surfaces owing to the difficulty of direct observations or physical evaluations. In this study, we prepared agar gels with fractal surfaces, which mimic the morphology and surface properties of biological surfaces, and used a new bio-surface model to observe the spreading behavior of liquids on the surfaces. Results of high-speed observation showed that the rough structure accelerated the spreading of water droplets and induced the appearance of a wicking front. Moreover, the addition of alcohol or colloidal particles induced the acceleration of wetting with Marangoni flow and the inhibition with assembling of particles. We have attempted to observe interfacial phenomena on biological interfaces and understand the fundamental laws of wetting dynamics. These findings can be applied to food, medical products, and cosmetic products.