Phylogenetic analysis of the scaling of wet and dry biological fibrillar adhesives

Abstract

Fibrillar, or ''hairy,'' adhesives have evolved multiple times independently within arthropods and reptiles. These adhesives exhibit highly desirable properties for dynamic attachment, including orientation dependence, wear resistance, and self-cleaning. Our understanding of how these properties are related to their fibrillar structure is limited, although theoretical models from the literature have generated useful hypotheses. We survey the morphology of 81 species with fibrillar adhesives to test the hypothesis that packing density of contact elements should increase with body size, whereas the size of the contact elements should decrease. We test this hypothesis in a phylogenetic context to avoid treating historically related species as statistically independent data points. We find that fiber morphology is better predicted by evolutionary history and adhesive mechanism than by body size. As we attempt to identify which morphological parameters are most responsible for the performance of fibrillar adhesives, it will be important to take advantage of the natural variation in morphology and the potentially suboptimal outcomes it encompasses, rather than assuming evolution to be an inherently optimizing process.contact splitting ͉ fibrillar adhesion ͉ setae ͉ phylogeny ͉ independent contrasts

Run don't walk: locomotor performance of geckos on wet substrates

“…Geckos have adapted their adhesive morphology in order to exploit various niches, perhaps not unlike Anolis, another pad-bearing group with clearly defined ecomorphological variation (Losos, 1990b;Vitt et al, 2003). Unlike Anolis, however, very few studies have focused on the relationship between gecko morphology and ecological niche, despite significant variation in digital and setal morphology (Gamble et al, 2012;Peattie and Full, 2007), both of which may be significant to the gecko's interaction with surface water. For instance, in this study we found that sprint performance on wet substrates is comparable among five taxonomically distinct species.…”

“…There are more than 1400 species of gecko, inhabiting many ecological niches and the gecko adhesive system has evolved multiple times (Gamble et al, 2012), with gains and losses correlated with habitat preference in at least one group (Lamb and Bauer, 2006). Despite this diversity, very few studies of adhesion have investigated species other than the Tokay gecko (Irschick et al, 1996;Niewiarowski et al, 2008;Russell and Higham, 2009), even though species of gecko do vary in several conspicuous ways related to adhesion, including morphology and behavior (Williams and Peterson, 1982;Peattie and Full, 2007;Gamble et al, 2012). Our primary goal with this study is to investigate the interaction between water and the gecko adhesive system under conditions that relax some of the standardized conditions typical of gecko laboratory performance studies.…”

Laser printing hierarchical structures with the aid of controlled capillary-driven self-assembly

“…One possible application of these structures is in microobject trap-release systems, which are intensively demanded in the fields of chemical analysis and biomedical devices and have drawn considerable attention from researchers. Some studies have revealed that the fibrillar structures exhibit wondrous adhesive or trapping properties in biological systems such as those of the beetle (28) and gecko (29,30). These kinds of bioinspired adhesive filaments can be developed in various technical applications.…”

An Internally Heated Shape Memory Polymer Dry Adhesive

“…Substantial investments in the study and development of dry adhesives have been made in recent years, spurred in large part by the discovery of the exceptional adhesive capabilities of gecko lizards [1]. The majority of this work has focused on the study of fibrillar, or "hairy", dry adhesives; natural examples such as OPEN ACCESS the gecko [2][3][4][5][6], or the development and characterization of artificial systems meant to mimic those found naturally [7][8][9][10].…”

“…Fibrillar structures are one possible solution to this problem; the slender fibrillar structures maximize compliance at the microscale to generate a large contact area, while the underlying structure supplies adequate rigidity to suppress peeling. Fibrillar adhesives are particularly effective when adhering to microscopically rough, irregular surfaces due to the extreme compliance of the fibers and their inherent contact splitting nature [6]. In addition, careful design of the fibers can allow for a large ratio of maximum adhesion to minimum adhesion, often termed adhesion "reversibility", which is typically highly desirable for dry adhesive systems and is essential for locomotion-based applications [8].…”