Large-Scale Spinning Approach to Engineering Knittable Hydrogel Fiber for Soft Robots

Abstract

Efforts to impart responsiveness to environmental stimuli in artificial hydrogel fibers are crucial to intelligent, shape-memory electronics and weavable soft robots. However, owing to the vulnerable mechanical property, poor processability, and the dearth of scalable assembly protocols, such functional hydrogel fibers are still far from practical usage. Herein, we demonstrate an approach toward the continuous fabrication of an electro-responsive hydrogel fiber by using the self-lubricated spinning (SLS) strategy. The polyelectrolyte inside the hydrogel fiber endows it with a fast electro-response property. After solvent exchange with triethylene glycol (TEG), the maximum tensile strength of the hydrogel fiber increases from 114 kPa to 5.6 MPa, far superior to those hydrogel fiber-based actuators reported previously. Consequently, the flexible and mechanical stable hydrogel fiber is knitted into various complex geometries on demand such as a crochet flower, triple knot, thread tube, pentagram, and hollow cage. Additionally, the electrochemical-responsive ionic hydrogel fiber is capable of acting as soft robots underwater to mimic biological motions, such as Mobula-like flapping, jellyfish-mimicking grabbing, sea worm-mimicking multi-degree of freedom movements, and human finger-like smart gesturing. This work not only demonstrates an example for the large-scale production of previous infeasible hydrogel fibers, but also provides a solution for the rational design and fabrication of hydrogel woven intelligent devices.

Recent Advances on Designs and Applications of Hydrogel Adhesives

“…Simple parts of complicated hydrogel structures can be achieved by physically cross-linking the dissipative networks with a flat plane or curved tube wall (Figure 18a). [148,149] Such a poor heterointerface provided by physical attachment is reliable for limited individual motion (Figure 18b) but is insufficient for sophisticated and synergetic exercise because skeleton joints require a constantly cyclic and frictional stretch. Unlike hydrogel-porous surface, where interlock of hydrogels with irregular channels contributes to interfacial toughness, gel-substrate interfaces for smooth substrate, especially containing water, [150] are too weak because of the low surface sliding friction coefficient.…”

Kinetically Tunable, Active Auxetic, and Variable Recruitment Active Textiles from Hierarchical Assemblies

“…The material filament composition—the foundation of the hierarchy—determines the base mechanical properties. [ 11 ] Active properties, such as variable stiffness and shape recovery, can be embedded within the textile hierarchy through the inclusion of an active filament, such as a hydrogel or shape memory polymer (SMP) filament, [ 12–14 ] or active bimorph/composite filament. [ 15–18 ]…”

“…[23,24] Woven and braided textile geometries, which are opposing rows of interlocked filaments or yarns, aggregate active 1D elements to produce a scalable and distributed surface that closely resembles the mechanical characteristics of the single active 1D element. [12,25,26] Alternatively, knitted textile geometries, which are loop-based structures, have been shown to behave like origami tessellation patterns, embedding variable surface topography and shapes into the textile geometry. [27][28][29][30][31] Active filaments reconfigured into weft knit geometries can accomplish complex actuation motions, include folding, curling, contraction, and corrugation.…”

“…The material filament composition-the foundation of the hierarchy-determines the base mechanical properties. [11] Active properties, such as variable stiffness and shape recovery, can be embedded within the textile hierarchy through the inclusion of an active filament, such as a hydrogel or shape memory polymer (SMP) filament, [12][13][14] or active bimorph/composite filament. [15][16][17][18] Yarn spinning-step two in the hierarchy-alters the mechanical properties of the original material filament by pre-stressing and constraining the materials in a helical geometry.…”

Smart Hydrogel Bilayers Prepared by Irradiation

“…Chen and co-workers designed a novel thermal-/NIR-responsive double network structure of hydrogel bilayers [ 9 ]. Many researchers developed soft actuators made by smart hydrogels, which will provide potential benefits for soft robots [ 10 , 11 , 12 ], artificial muscles [ 13 , 14 , 15 ], and drug delivery [ 16 ]. However, most of the existing studies used chemical reagents for cross-linking, and the preparation of hydrogel bilayers by gamma ray is rarely reported.…”