Bioinspired fibrillar adhesives: a review of analytical models and experimental evidence for adhesion enhancement by surface patterns

Abstract

Fibrillar structures are found on the attachment pads of insects and small reptiles. These structures enable exquisite conformation to rough surfaces, increase the number of van der Waals interactions between the structure and the target surface, and thus enhance adhesion.Biomimetic adhesives replicate this effect by patterning polymer films with micron-or submicron-sized protrusions. Numerical contact-mechanics models as well as experimental adhesion measurements have been reported for a variety of protrusion shapes including flat, rounded, mushroom and spatula geometries. Although superior adhesion has been reported for the mushroom and spatula tip geometries, straight, flat-tipped pillars offer the potential for much simpler mass-production such as by injection moulding and are thus the focus of this review.Existing models for straight, flat-tipped pillar arrays do not fully agree with reported experimental results. Analytical models are generally limited to elastic materials, and inherently assume that neighbouring pillars behave independently. For elastic pillars in close proximity, however, pillars do in fact interact mechanically, affecting adhesion. Moreover, visco-and hyper-elastic materials are often used in practice, yet dissipative effects receive little attention in analytical models. We find that no study has conclusively investigated the limit of adhesive strength achievable by fibrillar adhesives. It also remains unclear what happens to the adhesive strength as the areal density of contacting regions approaches 100%.

The multiple V-shaped double peeling of elastic thin films from elastic soft substrates

“…To this regard, several studies have been devoted to soft elastic contacts in presence of adhesion [11,[22][23][24][25], and specifically to the detachment process [26][27][28]. Experimental observations of insects and spiders [29][30][31] and theoretical studies [32][33][34] have made clear the crucial role played by highly flexible terminal spatula-shaped substructures attached to their legs, which finally allows them to easily climb on surfaces with different properties in terms of roughness and compliance.…”

Biomimetic wall-shaped adhesive microstructure for shear-induced attachment: the effects of pulling angle and preliminary displacement

“…Thin-film-ended hairy adhesive structures have evolved independently in insects, arachnids and reptiles to secure their locomotion on substrates of arbitrary orientation, geometry and chemical composition [1]. Since it was revealed that terminal thin-film elements operate using intermolecular [2,3] and, possibly, also capillary [4,5] forces, which allowed these structures to be replicated with engineering materials, much effort has been put into the development of biomimetic adhesive surfaces [6,7]. This led to the introduction of mushroom-shaped microstructures [8,9] mimicking the hairs evolved in male leaf beetles for passive long-term attachment during pairing [10,11].…”

Addressing Unmet Clinical Needs with UV Bioadhesives

“…The result is exquisite contact between adhesive and substrate and, subsequently, strong adhesion from weak interactions such as hydrogen bonding, exemplified in biomimetic dry adhesives. 75 Such intimate contact is shown in histology micrographs 21,27,68 in Figure 5. Physical adhesion can be enhanced via entanglement of polymer chains and collagen fibers, 54 which can occur in such close proximity.…”