Remoras are a family of fishes that can attach to other swimming organisms via an adhesive disc evolved from dorsal fin elements. However, the factors driving the evolution of remora disc morphology are poorly understood. It is not possible to link selective pressure for attachment to a specific host surface because all known hosts evolved before remoras themselves. Fortunately, the fundamental physics of suction and friction are mechanically conserved. Therefore, a morphologically relevant bioinspired model can be used to examine performance of hypothetical evolutionary intermediates. Using a bioinspired remora disc, we experimentally investigated the performance of increased lamellar number on shear adhesion. Herein, we translated fundamental biological principles into engineering design rules and show that a passive model system can autonomously achieve adhesive forces measured in live remoras in any environment. Our experimental results show that an increase in lamellar number resulted in an increase in shear adhesive performance, supporting the phylogenetic trend observed in extant remoras. The greatest pull-off forces measured for our model were on surface roughness on the order of shark skin and exceeded those measured for live remoras attached to shark skin by almost 60%. Overall, relative to fossil remoras and their closest ancestor, extant remoras exhibit a morphology indicative of selection for enhanced shear adhesive performance.

Function is a key central concept to the practice of biomimicry. Many published models of the biomimicry process include steps to identify, understand, and translate function of biological systems. Examples include functional modeling, decomposition, or abstraction with tools specifically designed to facilitate such steps. A functional approach to biomimicry yields a semantic bridge between biology and engineering, enabling practitioners from a variety of backgrounds to more easily communicate and collaborate in a biomimicry design process. Although analysis of function is likely a necessary part of biomimicry design, recent work suggests it is not sufficient without a more systematic understanding of the complex biological context in which a function exists (e.g., scale and trade-offs). Consequently, emerging tools such as ontologies are being developed that attempt to capture the intricacies of biological systems (including functions), such as their complex environmental and behavioral interactions. However, due to the complexity of such tools, they may be under-utilized. Here, we propose a solution through a computer-aided user interface tool which integrates a biomimetic ontology with a thesaurus-based functional approach to biomimicry. Through a proof of concept illustrative case study, we demonstrate how merging existing tools can facilitate the biomimicry process in a systematic and collaborative way, broadening solution discovery. This work offers an approach to making existing tools, specifically the BioMimetic Ontology, more accessible and encompassing of different perspectives via semantic translation and interface design. This provides the user with the opportunity to interface and extract information from both the Engineering-to-Biology Thesaurus and the BioMimetic Ontology in a way that was not possible before. The proposed E2BMO tool not only increases the accessibility of the BioMimetic Ontology, which ultimately aims to streamline engineers’ interaction with the bio-inspired design process, but also provides an option for practitioners to traverse biological knowledge along the way, encouraging greater interdisciplinary collaboration and consideration when conducting biomimicry research.

Research on gecko-based adhesion has become a truly interdisciplinary endeavour, encompassing many disciplines within the natural and physical sciences. Gecko adhesion occurs by the induction of van der Waals intermolecular (and possibly other) forces between substrata and integumentary filaments (setae) terminating in at least one spatulate tip. Gecko setae have increasingly been idealized as structures with uniform dimensions and a particular branching pattern. Approaches to developing synthetic simulacra have largely adopted such an idealized form as a foundational template. Observations of entire setal fields of geckos and anoles have, however, revealed extensive, predictable variation in setal form. Some filaments of these fields do not fulfil the morphological criteria that characterize setae and, problematically, recent authors have applied the term ‘seta’ to structurally simpler and likely non-adhesively competent fibrils. Herein we briefly review the history of the definition of squamate setae and propose a standardized classificatory scheme for epidermal outgrowths based on a combination of whole animal performance and morphology. Our review is by no means comprehensive of the literature regarding the form, function, and development of the adhesive setae of squamates and we do not address significant advances that have been made in many areas (e.g. cell biology of setae) that are largely tangential to their classification and identification. We contend that those who aspire to simulate the form and function of squamate setae will benefit from a fuller appreciation of the diversity of these structures, thereby assisting in the identification of features most relevant to their objectives.

It has been nearly 20 years since Autumn and colleagues established the central role of van der Waals intermolecular forces in how geckos stick. Much has been discovered about the structure and function of fibrillar adhesives in geckos and other taxa, and substantial success has been achieved in translating natural models into bioinspired synthetic adhesives. Nevertheless, synthetics still cannot match the multidimensional performance observed in the natural gecko system that is simultaneously robust to dirt and water, resilient over thousands of cycles, and purportedly competent on surfaces that are rough at drastically different length scales. Apparent insensitivity of adhesion to variability in roughness is particularly interesting from both a theoretical and applied perspective. Progress on understanding the extent to which and the basis of how the gecko adhesive system is robust to variation in roughness is impeded by the complexity of quantifying roughness of natural surfaces and a dearth of data on free-ranging gecko substrate use. Here we review the main challenges in characterizing rough surfaces as they relate to collecting relevant estimates of variation in gecko adhesive performance across different substrates in their natural habitats. In response to these challenges, we propose a practical protocol (borrowing from thermal biophysical ecological methods) that will enable researchers to design detailed studies of structure–function relationships of the gecko fibrillar system. Employing such an approach will help provide specific hypotheses about how adhesive pad structure translates into a capacity for robust gecko adhesion across large variation in substrate roughness. Preliminary data we present on this approach suggest its promise in advancing the study of how geckos deal with roughness variation. We argue and outline how such data can help advance development of design parameters to improve bioinspired adhesives based on the gecko fibrillar system.

The remarkable ability of geckos to adhere to a wide-variety of surfaces has served as an inspiration for hundreds of studies spanning the disciplines of biomechanics, functional morphology, ecology, evolution, materials science, chemistry, and physics. The multifunctional properties (e.g., self-cleaning, controlled releasability, reversibility) and adhesive performance of the gekkotan adhesive system have motivated researchers to design and fabricate gecko-inspired synthetic adhesives of various materials and properties. However, many challenges remain in our attempts to replicate the properties and performance of this complex, hierarchical fibrillar adhesive system, stemming from fundamental, but unanswered, questions about how fibrillar adhesion operates. Such questions involve the role of fibril morphology in adhesive performance and how the gekkotan adhesive apparatus is utilized in nature. Similar fibrillar adhesive systems have, however, evolved independently in two other lineages of lizards (anoles and skinks) and potentially provide alternate avenues for addressing these fundamental questions. Anoles are the most promising group because they have been the subject of intensive ecological and evolutionary study for several decades, are highly speciose, and indeed are advocated as squamate model organisms. Surprisingly, however, comparatively little is known about the morphology, performance, and properties of their convergently-evolved adhesive arrays. Although many researchers consider the performance of the adhesive system of Anolis lizards to be less accomplished than its gekkotan counterpart, we argue here that Anolis lizards are prime candidates for exploring the fundamentals of fibrillar adhesion. Studying the less complex morphology of the anoline adhesive system has the potential to enhance our understanding of fibril morphology and its relationship to the multifunctional performance of fibrillar adhesive systems. Furthermore, the abundance of existing data on the ecology and evolution of anoles provides an excellent framework for testing hypotheses about the influence of habitat microstructure on the performance, behavior, and evolution of lizards with subdigital adhesive pads.