Adhesion, friction, and compliance of bio-mimetic and bio-inspired structured interfaces

The remarkable mechanical properties of natural contact surfaces have inspired a great deal of interest and research in recent years. The underlying driver of this interest is the surprising range of surface mechanical properties such as adhesion, friction, and compliance that can be attained primarily by design of near-surface architecture using generic materials properties. A considerable literature has developed spanning the range from biological studies of structure and properties, through models to understand these properties, to development of bio-mimetic and bio-inspired structures, along with theory to understand how structure leads to development of surface mechanical properties. The literature has matured sufficiently that common architectures and principles have emerged, for which we attempt here to present a unified view. The field remains vibrant so we hope that this review can at the same time help in its further progress. Our goal in this paper is to review the field from the point of view of scientists and engineers interested to learn about the architecture, properties, and mechanisms of contacting surfaces in nature and how these might be mimicked to create new materials with unique and interesting properties. We begin with a brief description of natural systems, their architectures and properties, and follow by a discussion of the main bio-mimetic and bio-inspired materials that have been developed recently. We then discuss surface mechanical properties – adhesion, friction, and compliance – how these are related to materials and architectural parameters, and how these properties are measured. Where possible, we provide quantitative models for the relationship between structure and properties. We conclude the paper with a discussion of outlook and future possibilities in this field.