Friction modulation in limbless, three-dimensional gaits and heterogeneous terrains

Xiaotian Zhang,Noel Naughton,Tejaswin Parthasarathy,Mattia Gazzola

doi:10.1038/s41467-021-26276-x

Abstract

Motivated by a possible convergence of terrestrial limbless locomotion strategies ultimately determined by interfacial effects, we show how both 3D gait alterations and locomotory adaptations to heterogeneous terrains can be understood through the lens of local friction modulation. Via an effective-friction modeling approach, compounded by 3D simulations, the emergence and disappearance of a range of locomotory behaviors observed in nature is systematically explained in relation to inhabited environments. Our approach also simplifies the treatment of terrain heterogeneity, whereby even solid obstacles may be seen as high friction regions, which we confirm against experiments of snakes ‘diffracting’ while traversing rows of posts, similar to optical waves. We further this optic analogy by illustrating snake refraction, reflection and lens focusing. We use these insights to engineer surface friction patterns and demonstrate passive snake navigation in complex topographies. Overall, our study outlines a unified view that connects active and passive 3D mechanics with heterogeneous interfacial effects to explain a broad set of biological observations, and potentially inspire engineering design.

Highlights

Motivated by a possible convergence of terrestrial limbless locomotion strategies determined by interfacial effects, we show how both 3D gait alterations and locomotory adaptations to heterogeneous terrains can be understood through the lens of local friction modulation
Limbless locomotion is exhibited by a wide taxonomic range of slender creatures and has been observed in water[1], land[2,3,4,5], and even air[6]
Motivated by a possible evolutionary convergence of limbless movements determined by interfacial effects, the roles of both 3D body deformations and environmental heterogeneities are connected through, and modeled as, planar friction modulations

Summary

Introduction

Motivated by a possible convergence of terrestrial limbless locomotion strategies determined by interfacial effects, we show how both 3D gait alterations and locomotory adaptations to heterogeneous terrains can be understood through the lens of local friction modulation. The function Nðs; tÞ 1⁄4 ηN^ ðs; tÞ, with η being a normalization factor, models body lift as local weight redistribution, leading to effective-friction modulation along the snake.

Results

Conclusion