A state-of-the-art review and analysis on the design of dry adhesion materials for applications such as climbing micro-robots

Miniaturization of robotic systems has led to a demand for an alternative adhesive for use as the footpad of robots, with primary requirements of minimizing energy expenditure and satisfying performance and operational scenarios such as surveillance and reconnaissance. Inspired by nature, the dry adhesive concept as seen in climbing lizards such as the gecko has drawn significant interest from researchers. Adhesion in geckos is attributed to micro/nano fibrils found on its feet that rely on van der Waals forces to adhere to a surface, hence the terminology of dry adhesive. While immense progress has been made in the design and fabrication of multiscale hierarchical adhesive structures, the robustness, durability and endurance (ability to adhere to surfaces for an extended period of time) of gecko-foot mimetic dry adhesives still lags behind their biological counterparts. In this review article, we highlight the design considerations for the development of robust and durable bio-inspired synthetic adhesives. Current challenges and future directions are also highlighted for the design and development of robust and durable dry adhesive structures.