Biodegradable, Sustainable Hydrogel Actuators with Shape and Stiffness Morphing Capabilities via Embedded 3D Printing

Abstract

Despite the impressive performance of recent marine robots, many of their components are non‐biodegradable or even toxic and may negatively impact sensitive ecosystems. To overcome these limitations, biologically‐sourced hydrogels are a candidate material for marine robotics. Recent advances in embedded 3D printing have expanded the design freedom of hydrogel additive manufacturing. However, 3D printing small‐scale hydrogel‐based actuators remains challenging. In this study, Free form reversible embedding of suspended hydrogels (FRESH) printing is applied to fabricate small‐scale biologically‐derived, marine‐sourced hydraulic actuators by printing thin‐wall structures that are water‐tight and pressurizable. Calcium‐alginate hydrogels are used, a sustainable biomaterial sourced from brown seaweed. This process allows actuators to have complex shapes and internal cavities that are difficult to achieve with traditional fabrication techniques. Furthermore, it demonstrates that fabricated components are biodegradable, safely edible, and digestible by marine organisms. Finally, a reversible chelation‐crosslinking mechanism is implemented to dynamically modify alginate actuators' structural stiffness and morphology. This study expands the possible design space for biodegradable marine robots by improving the manufacturability of complex soft devices using biologically‐sourced materials.

Recent Progress in 3D Printing of Polymer Materials as Soft Actuators and Robots

“…The ink for extrusion-based printing should have shear-thinning behavior or sol-gel transition, which can be achieved through solvent exchange, charge shielding, temperature variation, and post-curing. − While extrusion-based printing has been extensively used in various hydrogel systems, it suffers low printing efficiency, relatively poor accuracy, and challenges in printing small and high-precision structures . In contrast, photocuring printing, especially voxel printing achieved by precise light source control, offers high precision and efficiency and favors printing more complex structures. ,,, The most widely used hydrogel systems for printed soft actuators and robots include polyacrylic acid (PAAc) gels, polyacrylamide (PAAm) gels, poly­( N -isopropylacrylamide) (PNIPAm) gels, , hyaluronic acid gels, chitosan gels, and alginate gels …”

Three-Dimensional Printing Strategies for Enhanced Hydrogel Applications

“…The field of soft and marine robotics has also seen innovative applications of 3D printing technologies. The fabrication of jellyfish-mimic soft robot actuators [4] and biodegradable hydrogel actuators [46] illustrates the potential of these technologies in developing devices that operate effectively in challenging environments. Furthermore, the advancement in material properties, such as full-color luminescence and opacity tuning [3], enhances the adaptability and utility of robotic systems.…”

Sustainable Morphing Matter: Design and Engineering Practices

“…For example, self‐healing materials can be used to fix damages on wearable devices and allow for new shape and function reconfigurations of a handheld controller by breaking and rejoining the dynamic bonds. [ 21,94,95 ] (iii) Systems designed with morphing matter that evolve over time, through techniques such as self‐organizing, [ 96 ] phase shifting, [ 97 ] self‐growth, [ 98,99 ] and controlled degradation, destruction, and evolution [ 100,101 ] may also achieve multi‐functionalities. Additionally, morphing matter can promote sustainability by serving ecological purposes.…”