Abstract
Millions of years’ evolution has imparted life on earth with excellent environment adaptability. Of particular interest to scientists are some plants capable of macroscopically and reversibly altering their morphological and mechanical properties in response to external stimuli from the surrounding environment. These intriguing natural phenomena and underlying actuation mechanisms have provided important design guidance and principles for man-made soft robotic systems. Constructing bio-inspired soft robotic systems with effective actuation requires the efficient supply of mechanical energy generated from external inputs, such as temperature, light, and electricity. By combining bio-inspired designs with stimuli-responsive materials, various intelligent soft robotic systems that demonstrate promising and exciting results have been developed. As one of the building materials for soft robotics, hydrogels are gaining increasing attention owing to their advantageous properties, such as ultra-tunable modulus, high compliance, varying stimuli-responsiveness, good biocompatibility, and high transparency. In this review article, we summarize the recent progress on plant-inspired soft robotics assembled by stimuli-responsive hydrogels with a particular focus on their actuation mechanisms, fabrication, and application. Meanwhile, some critical challenges and problems associated with current hydrogel-based soft robotics are briefly introduced, and possible solutions are proposed. We expect that this review would provide elementary tutorial guidelines to audiences who are interested in the study on nature-inspired soft robotics, especially hydrogel-based intelligent soft robotic systems.
Highlights
As Charles Darwin once said, it is not the strongest of the species that survives, nor the most intelligent; it is the one most adaptable to change [1]
We aim to summarize recent progress on the development of hydrogel-based soft robotics with plant-inspired designs and actuation mechanisms
We models for the design and fabrication of soft robotics [25]
Summary
As Charles Darwin once said, it is not the strongest of the species that survives, nor the most intelligent; it is the one most adaptable to change [1]. In response to changes in relative humidity, pinecone [9] opens/closes its scales to release its seeds, while wheat awn [10] does so by bending/unbending its seed dispersal units. Instead of responding to the humidity change, ice plant opens its protective valves to release the seeds only when the seed capsule is sufficiently hydrated with liquid water, which ensures that the seeds are dispersed under favorable conditions for germination [11] Another fascinating nastic movement of plants is the folding/unfolding response to external mechanical stimulus (e.g., touch or vibration). The underlying actuation mechanism for each type of nastic movement and the derivation of the design principles for biomimetic soft robotics are discussed
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