4D printing with smart materials for soft robots
Creators: name: Wang, Yueping
Publisher: name: No Publisher Supplied
Year: 2023

description: Soft robotics is an emerging research field that considers the design, fabrication, and control of robotic systems by involving compliant materials that offer benefits such as excellent conformability and high safety. Though the traditional cast-molding method could enable the easy realization of soft robots based on silicone rubber, their geometric complexity and functional versatility were extremely limited. Taking advantage of additive manufacturing (AM) or three-dimensional (3D) printing, rapid prototyping, structural sophistication, and functional enrichment can be ensured as well as a broader selection of materials. To date, smart materials such as hydrogel, shape memory polymer (SMP), and liquid crystal elastomer (LCE) are gaining growing attention for their extensive employment in soft robotics and 3D printing. The combination of smart materials and 3D printing is referred to as four-dimensional (4D) printing because the form of printed objects, such as shape and properties, can be transformed over time, the fourth dimension. In order to explore the improvement toward robotic performance and printing capability, this dissertation focuses on endowing extraordinary features of SMP and LCE to soft robots and 4D printing. On the one hand, the great temperature-responsive tunable stiffness of SMP was exploited to produce a large-scaled soft robot with reconfigurable and deactivatable skeletons so that the robot can exhibit either gravity resistance or flexibility depending on requirements. Instead of adopting exterior heat convection, a micro-sized liquid metal was embedded into the SMP skeleton to enable efficient resistive heating. Equipped with the proposed soft robots, a robotic gripper with a high aspect ratio of 15:1 was highlighted to grasp large-sized objects, and an amphibious robot with reconfigurable limbs capable of swimming underwater and fast-moving on rugged or flat lands was demonstrated. On the other hand, LCEs exhibit reversible mechanical deformation along the direction of LC (i.e., mesogen) alignment in response to various external stimuli, indicating huge potential in the development of smart products. To highlight the advancement of LCEs in 4D printing, in addition to an innovative LCE material formulation to provide the printable resin, a contactless magnetic-field alignment strategy was incorporated with a customized digital light processing (DLP) printing system to enable the effective programmed LC alignment and photopolymerization. The resulting LCEs could exhibit a large reversible actuation strain of more than 35 %. Moreover, the capability of local LC alignment and selective polymerization was characterized so that constructing smart structures with more delicate shape-morphing were accessible. Several proof-of-concept LCE prototypes such as flowers and photo-activated crawlers were demonstrated to have as-expected reversible behaviors. Through exploring the advancement of smart materials in 4D printing and soft robotics, this dissertation presents several structures/devices with extraordinary functionalities using SMP and LCE, revealing a broad spectrum of smart materials’ applications in the future world.