Dimensional effects of surface morphology and trapped air on mammalian cell adhesion to special wetting surfaces

Materials with special wettability have broad biomedical applications, including the control of mammalian cell adhesion and inhibiting biofilm formation. However, limited understanding of mammalian cellular responses to superhydrophobic materials with trapped air restricts their clinical applications. In this study, we fabricated materials with varied nanostructures and wettability, and systematically compared short-term mammalian cellular responses in the presence and absence of trapped air. Our results show that small nanostructures generate small, often invisible air bubbles at the solid-liquid interface when in contact with mammalian cell suspensions. In the presence of these small bubbles, the number of adhered cells was comparable to both the same sample without trapped air and its hydrophilic counterpart, contradicting the intuitive expectations that trapped air would reduce cell adhesion. In contrast, larger nanostructures resulted in visible, hundred-micron-sized air bubbles, which significantly inhibited cell adhesion. This effect was evident when comparing the same superhydrophobic sample with and without trapped air, as well as against hydrophilic counterparts with the same morphology. Further tracking of large air bubbles on the hydrophobic materials revealed that no cells adhered to the areas occupied by hundred-micron-sized air bubbles, while more cells accumulated at the solid-liquid-gas triple line. Hence, this work deepens the understanding of cellular responses to superhydrophobic materials, revealing that material structure size influences the size of trapped air and subsequently dominates cell adhesion.