Mechanical Innovations of a Climbing Cactus: Functional Insights for a New Generation of Growing Robots.

Patricia Soffiatti,Nick P Rowe

doi:10.3389/frobt.2020.00064

Abstract

Climbing plants are being increasingly viewed as models for bioinspired growing robots capable of spanning voids and attaching to diverse substrates. We explore the functional traits of the climbing cactus Selenicereus setaceus (Cactaceae) from the Atlantic forest of Brazil and discuss the potential of these traits for robotics applications. The plant is capable of growing through highly unstructured habitats and attaching to variable substrates including soil, leaf litter, tree surfaces, rocks, and fine branches of tree canopies in wind-blown conditions. Stems develop highly variable cross-sectional geometries at different stages of growth. They include cylindrical basal stems, triangular climbing stems and apical star-shaped stems searching for supports. Searcher stems develop relatively rigid properties for a given cross-sectional area and are capable of spanning voids of up to 1 m. Optimization of rigidity in searcher stems provide some potential design ideas for additive engineering technologies where climbing robotic artifacts must limit materials and mass for curbing bending moments and buckling while climbing and searching. A two-step attachment mechanism involves deployment of recurved, multi-angled spines that grapple on to wide ranging surfaces holding the stem in place for more solid attachment via root growth from the stem. The cactus is an instructive example of how light mass searchers with a winged profile and two step attachment strategies can facilitate traversing voids and making reliable attachment to a wide range of supports and surfaces.

Highlights

Plants have recently become a focus of interest as potential bioinspired models for soft robotics (Mazzolai et al, 2014; Walker, 2015; Mazzolai, 2017; Del Dottore et al, 2018)
The stem biomechanics in climbing and searching stems of this plant are characterized by a light-biomass architecture of thinwalled tissue which needs to be turgescent to retain stiffness
The combination of succulence and turgescence, searchers with star-shaped geometries as well as a two-step attachment strategy, provides a novel combination of functional traits that might be considered as potential innovations for new climbing plant-like robots

Summary

Introduction

Plants have recently become a focus of interest as potential bioinspired models for soft robotics (Mazzolai et al, 2014; Walker, 2015; Mazzolai, 2017; Del Dottore et al, 2018). Plants offer a rich source of potential innovations because of (i) their many kinds of growth and movement by growth (ii) their modular construction and strategically positioned functional structures and specialized organs and (iii) their morphological and functional plasticity—in particular their ability to make simple changes in developmental to profoundly change structural properties and functionality. The combination of these life history processes bestows high levels of adaptability in biological contexts and offers a wide adaptive potential for technological applications. Climbing plants are providing a lot of choice for bioinspired technologies in robotics (Mehling et al, 2006; Wooten and Walker, 2016, 2018; Fiorello et al, 2018, 2019, 2020; Wooten et al, 2018; Must et al, 2019)

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