From micro to nano contacts in biological attachment devices

Abstract

Animals with widely varying body weight, such as flies, spiders, and geckos, can adhere to and move along vertical walls and even ceilings. This ability is caused by very efficient attachment mechanisms in which patterned surface structures interact with the profile of the substrate. An extensive microscopic study has shown a strong inverse scaling effect in these attachment devices. Whereas m dimensions of the terminal elements of the setae are sufficient for flies and beetles, geckos must resort to sub-m devices to ensure adhesion. This general trend is quantitatively explained by applying the principles of contact mechanics, according to which splitting up the contact into finer subcontacts increases adhesion. This principle is widely spread in design of natural adhesive systems and may also be transferred into practical applications.walking ͉ adhesion ͉ locomotion ͉ legs ͉ insects A ttachment structures have independently developed several times in animal evolution (1, 2). Setose or hairy systems of various animal groups, such as insects, spiders, and lizards contain surfaces covered by fine patterns of protuberances of different origin. These highly specialized structures are not restricted to one particular area of the leg and may be located on different derivatives of the tarsus and pretarsus (3). Even among insects, the protuberances belong to different types: representatives of the Coleoptera and Dermaptera have setae with sockets providing additional mobility of setae, whereas representatives of Diptera have setae without sockets (acanthae). Setae range in their length from several millimeters to a few micrometers (4).Despite Ͼ300 years of studies on hairy attachment systems, there is still a debate concerning the attachment mechanism of animals walking on smooth walls or ceilings. Different hypotheses have been proposed to explain the mechanism of attachment: sticking fluid, microsuckers, and electrostatic forces (5). Based on experimental data, some of these theories have been rejected, and adhesion has been attributed to a combination of molecular interactions and capillary attractive forces mediated by secretions (6) or purely van der Waals interactions (7). Because some animals produce secretory fluids (insects) (8-10) in the contact area, whereas others do not (spiders, geckos) (11, 12), one can expect different basic physical forces contributing to the overall adhesion. Recently, strong evidence has been presented (13) that the adhesion of gecko setae is caused by van der Waals interaction, rejecting mechanisms relying on capillary adhesion. Elements of contact mechanics have also been applied to this problem (13,14); it was predicted that arrays with smaller setae endings should result in greater adhesive strength. In the present study, we combine an extensive microscopical study ¶ of biological surface devices with the theory of contact mechanics based on molecular adhesion. We will show that the scaling of the surface protuberances, for animals differing in weight by 6 orders of magnitude, ca...

Fabrication and adhesion of hierarchical micro-seta

“…For the secondary setae samples, the adhesion strengths of sample 3 are larger than those of sample 2, which are larger than those of sample 1. These results are consistent with the "contact splitting" principle [37]. If one spherical large contact area is subdivided into n smaller contacts, with an identical apparent contact area, the adhesion force rises by a factor n 1/2 .…”

Wet Chemical Processing

“…This theory states that adhesive force is proportional to the length of the contact; therefore, by splitting up the contact zone into many small areas of contact, the total adhesive force can be increased by the square root of the density of these small areas [23]. This principle clearly applies to wet adhesion.…”

Addressing Grand Challenges In Organismal Biology: The Need For Synthesis

“…A new moreexpansive systems biology that extends from genes through development, organismal phenotypes and function in natural settings demands that we approach our discipline using a much broader set of tools, including modeling and engineering approaches (figure 1). For example, biologists examining the ability of gecko lizards to run on walls and across ceilings collaborated with engineers to understand nanoscale adhesion and how toe pad orientation and gait allow the toes to repeatedly grip and release (Autumn et al 2000, Arzt et al 2003, Tian et al 2006, Wan et al 2012). This knowledge stimulated engineers and material scientists to develop novel types of dry adhesives (Ge et al 2007, Lee HS et al 2007, Lee JH et al 2009, Murphy et al 2009, Filippov et al 2011.…”