Staying Dry and Clean: An Insect’s Guide to Hydrophobicity

SIMPLE SUMMARY: Insects possess microscopic cuticular surface structures of different magnitudes. Such nano-, micro-, macro- and hierarchical structures often result in multifunctionality. In this review, we focus on hydrophobicity of the insect cuticle, since it often gives rise to other functions such as self-cleaning, anti-fogging, and anti-microbial activity. To do this, we reviewed the scientific literature on hydrophobic and superhydrophobic structures in insects. We found many insects possess unique structures and surface chemicals that make the cuticle waterproof. Among the many examples, we selected a few prominent ones to show the contribution of different levels of cuticular structures, as well as chemistry, in achieving hydrophobicity. We also discuss some instances of modern insect-inspired hydrophobic engineering designs. We show that insects are a great reservoir of inspiration for the guided design of novel materials with hydrophobic functionalities. Moreover, we also impart valuable insights on how material surfaces are important for biological systems. ABSTRACT: Insects demonstrate a wide diversity of microscopic cuticular and extra-cuticular features. These features often produce multifunctional surfaces which are greatly desired in engineering and material science fields. Among these functionalities, hydrophobicity is of particular interest and has gained recent attention as it often results in other properties such as self-cleaning, anti-biofouling, and anti-corrosion. We reviewed the historical and contemporary scientific literature to create an extensive review of known hydrophobic and superhydrophobic structures in insects. We found that numerous insects across at least fourteen taxonomic orders possess a wide variety of cuticular surface chemicals and physical structures that promote hydrophobicity. We discuss a few bioinspired design examples of how insects have already inspired new technologies. Moving forward, the use of a bioinspiration framework will help us gain insight into how and why these systems work in nature. Undoubtedly, our fundamental understanding of the physical and chemical principles that result in functional insect surfaces will continue to facilitate the design and production of novel materials.