4D Printing of Humidity‐Driven Seed Inspired Soft Robots

Abstract

Geraniaceae seeds represent a role model in soft robotics thanks to their ability to move autonomously across and into the soil driven by humidity changes. The secret behind their mobility and adaptivity is embodied in the hierarchical structures and anatomical features of the biological hygroscopic tissues, geometrically designed to be selectively responsive to environmental humidity. Following a bioinspired approach, the internal structure and biomechanics of Pelargonium appendiculatum (L.f.) Willd seeds are investigated to develop a model for the design of a soft robot. The authors exploit the re‐shaping ability of 4D printed materials to fabricate a seed‐like soft robot, according to the natural specifications and model, and using biodegradable and hygroscopic polymers. The robot mimics the movement and performances of the natural seed, reaching a torque value of ≈30 µN m, an extensional force of ≈2.5 mN and it is capable to lift ≈100 times its own weight. Driven by environmental humidity changes, the artificial seed is able to explore a sample soil, adapting its morphology to interact with soil roughness and cracks.

A Bioinspired Plasmonic Nanocomposite Actuator Sunlight‐Driven by a Photothermal‐Hygroscopic Effect for Sustainable Soft Robotics

“…[ 54 ] Finally, the proposed technology could be used to also develop energy harvesting applications based on photomechanical effects [ 55 ] stimulated by daily environmental variations, as well as bioinspired systems for environmental exploration, including, e.g., artificial seeds able to adaptively explore soils. [ 56 ]…”

Recent Advances in the Additive Manufacturing of Stimuli‐Responsive Soft Polymers

“…[377][378][379] These polymers offer fascinating dynamic and biomimetic responses, which permit them to develop structures for sensors, soft robots, artificial muscles, and smart electronic devices. [291,[380][381][382] 3D printing of humidity-responsive polymers enables the development of intricate and programmable structures. [383][384][385] Sometimes, humidity-responsive polymers are designed to enhance the mechanical properties of 3D-printed structures.…”

“…[530][531][532][533] Recent studies showed the development of smart grippers, actuators, and robots for different applications. [534][535][536][537][538][539][540] For instance, Cecchini et al [381] exploited the reshaping ability of humidityresponsive materials to develop a seed-like soft robot by using FDM printing, as illustrated in Figure 17A. In this approach, PCL-based filament were used to print a passive layer and electrospun cellulose nanocrystals (CNCs)/polyethylene oxide (PEO)based was used as an active layer to develop bilayer hygroscopic structures.…”

“…[ 377–379 ] These polymers offer fascinating dynamic and biomimetic responses, which permit them to develop structures for sensors, soft robots, artificial muscles, and smart electronic devices. [ 291,380–382 ]…”

“…Reproduced under the terms of the CC‐BY license. [ 381 ] Copyright 2023, The Authors, Advanced Science published by Wiley‐VCH GmbH. B) Rolling direction of LCE‐based robot fabricated by using DIW printing.…”