Frictional-anisotropy-based systems in biology: structural diversity and numerical model

Abstract

There is a huge variety in biological surfaces covered with micro- and nanostructures oriented at some angle to the supporting surface. Such structures, for example snake skin, burr-covered plant leaves, cleaning devices and many others cause mechanical anisotropy due to different friction or/and mechanical interlocking during sliding in contact with another surface in different directions. Such surfaces serve propulsion generation on the substrate (or within the substrate) for the purpose of locomotion or for transporting items. We have theoretically studied the dependence of anisotropic friction efficiency in these systems on (1) the slope of the surface structures, (2) rigidity of their joints, and (3) sliding speed. Based on the proposed model, we suggest the generalized optimal set of variables for maximizing functional efficiency of anisotropic systems of this type. Finally, we discuss the optimal set of such parameters from the perspective of biological systems.

Enhanced Locomotion Efficiency of a Bio-inspired Walking Robot using Contact Surfaces with Frictional Anisotropy

“…In general, anisotropy of surface micro- and nanostructures in biological surfaces are wide-spread and serve a variety of different functions6 such as locomotion, fluid/particle transportation, fixation, etc. Although we have observed promising results employing shark skin to enhance locomotion efficiency of our walking robot, we have to stress that we do not propose employing shark skin in future industrial robotic applications.…”

“…These attachment devices can provide optimal friction for forward motion, protect animals from slipping on a surface, and even allow them grip surfaces firmly. From this point of view, several works have investigated biological materials678910 and used them as an inspiration to develop materials1112 for robotic applications1314151617.…”

A glimpse of superb tribological designs in nature

“…these hairy systems is strongly dependent on the stiffness of the joints between directional hairs and supporting layers, which could be optimized (54). The frequency and velocity of sliding movement also remarkably affects the degree of friction anisotropy (54).…”

Remarkable Natural Material Surfaces and Their Engineering Potential

“…Frictional anisotropy can be found in a plethora of natural and artifi cial systems, ranging from burr-covered plant leaves and global plate tectonics to the textures and structures of certain solids at the molecular level. In snakes, frictional anisotropy is considered to be a result of preferred orientation of the micro-scale surface (Filippov and Gorb 2013 ). Frictional anisotropy plays a critical role in snake motion and the mechanics of its propulsion.…”