Hierarchical structures of cactus spines that aid in the directional movement of dew droplets

Abstract

Three species of cactus whose spines act as dew harvesters were chosen for this study: Copiapoa cinerea var. haseltoniana , Mammillaria columbiana subsp. yucatanensis and Parodia mammulosa and compared with Ferocactus wislizenii whose spines do not perform as dew harvesters. Time-lapse snapshots of C. cinerea showed movement of dew droplets from spine tips to their base, even against gravity. Spines emanating from one of the areoles of C. cinerea were submerged in water laced with fluorescent nanoparticles and this particular areole with its spines and a small area of stem was removed and imaged. These images clearly showed that fluorescent water had moved into the stem of the plant. Lines of vascular bundles radiating inwards from the surface areoles (from where the spines emanate) to the core of the stem were detected using magnetic resonance imaging, with the exception of F. wislizenii that does not harvest dew on its spines. Spine microstructures were examined using SEM images and surface roughness measurements ( R a and R z ) taken of the spines of C. cinerea . It was found that a roughness gradient created by tapered microgrooves existed that could potentially direct surface water from a spine tip to its base. This article is part of the themed issue ‘Bioinspired hierarchically structured surfaces for green science’.

Elastic and collapsible: current understanding of cell walls in succulent plants

“…Another disadvantage of CoMPP is the difficulty of isolating succulent tissues within a succulent organ, which is not feasible in most cases and requires whole organs. The latest technological developments include imaging techniques that allow for three-dimensional visualization of cell wall structure, composition, and connectivity, including serial-sectioning scanning electron microscopy (ssSEM; Oi et al , 2017 ; Harwood et al, 2020 , 2021 ; Antreich et al , 2021 ) among other high-resolution microscopy techniques ( Zeng et al , 2017 ; Haas et al , 2020 ), X-ray microcomputed tomography (X-ray microCT; Théroux-Rancourt et al , 2017 ; Earles et al , 2018 ), and magnetic resonance imaging (MRI; Malik et al , 2016 ; Hesse et al , 2020 ; Mylo et al , 2021 ). These methods have the potential to elucidate how succulent tissues are built and to reveal their anatomical complexity from a three-dimensional perspective.…”

Direct force measurement of microscopic droplets pulled along soft surfaces

“…Wetting is a phenomenon ubiquitous in both nature and industry, ranging from dew collection in cacti 1 to flexible printable electronics 2 . While research on droplet-surface interactions has been an active field of research for decades, much of the work has focussed on droplets on a stiff substrate, where surface tension forces are unable to deform the substrate beyond the atomic scale 3 .…”

Grooves Accelerate Dew Shedding

“…Previous studies have developed ultrasmooth or micropatterned coated substrates [14][15][16][17][18][19][20][21][22] which favor drop nucleation and reduce R c , but these studies have only considered a steady condensation. Here, we focus on the transient regime and study how micro-grooves, inspired by observations of condensation on horizontal grooved surfaces [14,16] and natural organisms living in arid environments [23][24][25], allow us to reach R c earlier. Presumably, such microgrooves without chemical coating and manufacturable as one piece of strong material [26] could be made resilient to weathering.…”