Artificial Tendrils Mimicking Plant Movements by Mismatching Modulus and Strain in Core and Shell

Abstract

Motile organs have evolved in climbing plants enabling them to find a support and, after secure attachment, to reach for sunlight without investing in a self-supporting stem. Searching movements, the twining of stems, and the coiling of tendrils are involved in successful plant attachment. Such coiling movements have great potential in robotic applications, especially if they are reversible. Here, the underlying mechanism of tendril movement based on contractile fibers is reported, as illustrated by a function-morphological analysis of tendrils in several liana species and the encoding of such a principle in a core-shell multimaterial fiber (MMF) system. MMFs are composed of a shape-memory core fiber (SMCF) and an elastic shell. The shape-memory effect of the core fibers enables the implementation of strain mismatch in the MMF by physical means and provides thermally controlled reversible motion. The produced MMFs show coiling and/or uncoiling behavior, with a high reversible actuation magnitude of ≈400%, which is almost 20 times higher compared with similar stimuli for sensitive soft actuators. The movements in these MMFs rely on the crystallization/melting behavior of oriented macromolecules of SMCF.

Liquid Crystal Elastomer Artificial Tendrils with Asymmetric Core–Sheath Structure Showing Evolutionary Biomimetic Locomotion

“…Besides the asymmetric LC mesogen orientation, other biomimetic dorsiventral asymmetries, such as the noncentric semi‐ellipse cross‐section, may also contribute to asymmetric contraction and helical deformation via a synergistic effect. It should be noted that similar helical winding/coiling deformations are found in other multimaterial systems with mismatching strain, such as core–shell multimaterial fibers [ 18 ] and hydrogel/gold bilayer ribbons. [ 65 ] The difference in the shape‐changing mechanism of the multimaterial systems is that the helical winding/coiling deformations are induced by mismatching strain/stress generated in different materials during the shape‐memory/elastic recovery 18 or swelling and deswelling process.…”

“…[ 3 ] Through learning from natural intelligence and studying the basic principle of structure–functions of biology, materials scientists and engineers have recently started to devise and fabricate various stimuli‐responsive shape‐morphing materials for envisioned applications in a wide range of areas such as soft robots and artificial muscles. [ 7–18 ] Among these stimuli‐responsive materials, liquid crystal elastomers (LCEs) [ 17,19–22 ] have been recognized as the most promising candidate for mimicking the haptonastic movements of living organisms because of their versatility in creating shape‐morphing modes, such as bending, [ 23–26 ] oscillating, [ 27–32 ] rotation, [ 28,32,33 ] rolling, [ 34–37 ] swimming, [ 38–40 ] twisting, [ 41,42 ] crawling, [ 43 ] jumping [ 44,45 ] and lift‐off and landing. [ 46 ] For example, Priimagi and coworkers [ 47 ] demonstrated a light‐powered LCE flytrap that is capable of executing spontaneous snapping and intelligent recognization of different micro‐targets via perceiving their physical properties.…”

Bio-Inspired Magnetically Controlled Reversibly Actuating Multimaterial Fibers

“…Formation of MMFs: A process similar to the one defined in [18] was adopted. Two PTFE tubes with 1 and 2 mm diameter were used as molds.…”

“…These approaches not only require complex synthesis strategies, but mostly allow only one-way movements, where the material can take the shape of a contracted, coiled spring upon the application of external stimuli. Most recently, we reported multimaterial fibers based on a shape-memory core fiber (SMCF) and an elastomeric shell, where the reversible movements were reported upon cyclic heating and cooling, i.e., a reversible contracting-expanding spring-like movement [18]. The reversible shape-memory effect in semi-crystalline polymer networks is their ability to actuate between two temporary shapes upon programming and the subsequent stimulation by an external stimulus.…”

From Nature to Technology: Exploring Bioinspired Polymer Actuators via Electrospinning

“…They possess specialized fibrous structures, such as tendrils, which wrap Climbing plants, like vines, employ thigmotropism to sense and respond to physical contact [47]. They possess specialized fibrous structures, such as tendrils, which wrap around support structures when they come into contact with them [48]. By doing so, these plants can grow and climb upward, utilizing external structures for stability and support.…”