Abstract
Stimuli-responsive hydrogels are candidate building blocks for soft robotic applications due to many of their unique properties, including tunable mechanical properties and biocompatibility. Over the past decade, there has been significant progress in developing soft and biohybrid actuators using naturally occurring and synthetic hydrogels to address the increasing demands for machines capable of interacting with fragile biological systems. Recent advancements in three-dimensional (3D) printing technology, either as a standalone manufacturing process or integrated with traditional fabrication techniques, have enabled the development of hydrogel-based actuators with on-demand geometry and actuation modalities. This mini-review surveys existing research efforts to inspire the development of novel fabrication techniques using hydrogel building blocks and identify potential future directions. In this article, existing 3D fabrication techniques for hydrogel actuators are first examined. Next, existing actuation mechanisms, including pneumatic, hydraulic, ionic, dehydration-rehydration, and cell-powered actuation, are reviewed with their benefits and limitations discussed. Subsequently, the applications of hydrogel-based actuators, including compliant handling of fragile items, micro-swimmers, wearable devices, and origami structures, are described. Finally, challenges in fabricating functional actuators using existing techniques are discussed.
Highlights
Recent advances in 3D printing have enabled the production of customizable hydrogel-based actuators with a variety of applications
A focused synopsis of the fabrication techniques and challenges for 3D printing hydrogel-based actuators has not been previously reported. This mini-review presents recent advancements in 3D printing for fabricating hydrogel actuators, either as a standalone manufacturing process or integrated with traditional fabrication techniques, where actuators are defined as any components that perform defined movements or geometric changes
We provide a focused survey on the challenges and limitations in fabricating hydrogel actuators using existing 3D printing techniques to inspire future hydrogel fabrication advances that improve the performance of hydrogel-based actuators
Summary
Recent advances in 3D printing have enabled the production of customizable hydrogel-based actuators with a variety of applications. Hydrogels are hydrophilic and porous crosslinked polymer networks whose mechanical, chemical, and stimulation-responsive properties can be tuned based on composition and manufacturing processes (Shi et al, 2019) Such properties enable applications of hydrogels in several domains, including tissue engineering (Billiet et al, 2012), drug delivery (Li and Mooney, 2016), wound dressings (Varaprasad et al, 2020), and soft robotics (Lee et al, 2020; Wallin et al, 2018). To address this gap, this mini-review presents recent advancements in 3D printing for fabricating hydrogel actuators, either as a standalone manufacturing process or integrated with traditional fabrication techniques, where actuators are defined as any components that perform defined movements or geometric changes. We provide a focused survey on the challenges and limitations in fabricating hydrogel actuators using existing 3D printing techniques to inspire future hydrogel fabrication advances that improve the performance of hydrogel-based actuators
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