Patterned Aluminum/Polydimethylsiloxane-Laminated Film for a Solvent-Driven Soft Actuator with Programmable and Multistable Shape Morphing

Recently, soft actuators capable of deforming in predictable ways under external stimuli have attracted increasing attention by showing great potential in emerging industries. However, limited efforts are being spent on the untethered actuators with multistable deformations. Also, there is a lack of mechanically guiding design principles for multistable structures. Here, the patterned aluminum/polydimethylsiloxane (Al/PDMS)-laminated films with surface wrinkles are fabricated by magnetron sputtering the Al layer on the PDMS substrate. By tuning the geometric parameters and surface constraints of the patterned Al/PDMS-laminated films, a series of solvent-driven actuators with multiform stable configurations (such as monostable arc, multistable cylinder, and monostable/bistable spiral) are proposed. The deformation mechanism is revealed using a linear elastic theory. Combined with the finite element analysis method, the deformations of Al/PDMS-laminated films with different surface constraints and geometric configurations are visually predicted. Besides, we modulate the deformation of different parts of the Z-shaped actuators by tuning the surface constraints in different regions of the Z-shaped Al/PDMS bilayer films to achieve multiple stable deformations in a single actuator. The concept offers a huge design scope for reconfigurable soft robots. Finally, two bionic applications are proposed to demonstrate the practical applications of the soft solvent-driven actuator based on the patterned Al/PDMS films in artificial muscles and bionic robotics. This work provides a strategy for the design and fabrication of programmable and controllable soft actuators, laying the foundation for a wide range of applications in smart materials.

Programmable Deformations of Biomimetic Composite Hydrogels Embedded with Printed Fibers

Shape deformations are prevalent in nature, which are closely related to the heterogeneous structures with a feature of fibrous elements embedded in a matrix. The microfibers with specific orientations act as either passive geometrical constraints in an active matrix or active elements in a passive matrix, which generate programmed internal stresses and drive shape morphing under external stimuli. Morphing materials can be designed in a biomimetic way, yet it is challenging to fabricate composite hydrogels with well-distributed fibers by a facile strategy. Here, we demonstrate the fabrication of microfiber-embedded hydrogels facilitated by the extrusion-based printing technology. Programmed deformations are achieved in these hydrogels with microfibers distributed in the upper and/or bottom layers of the gel matrix. Under external stimuli, the microfibers and the gel matrix have different responses that produce internal stresses and result in programmable deformations of the composite gel. Multiple shape transformations are realized in the hydrogel by embedding multiple types of responsive microfibers in the passive or active matrix, which is fabricated with the assistance of multinozzle printing. A soft hook is designed to show the capacity of the composite hydrogel to hold and move an object in a saline solution. This facile and versatile strategy provides an alternative way to prepare biomimetic hydrogels with potential applications in biomedical devices, flexible electronics, and soft robots.