Mechanically Robust Anisotropic Hydrogel–Organogel Conjugates for Soft Actuators with Fast Response Time and Diverse Bi-Axial Programmable Folding Ability

Anisotropic soft materials possessing adequate mechanical strength and hysteresis-free actuation with fast response time are necessary to mimic the actuation ability of natural systems. Furthermore, the ability of these systems to modulate the directionality of anisotropic behavior is desirable to realize multi-axial folding patterns. In this report, a general yet scalable strategy involving physical interpenetration of independent hydrogel and organogel networks is utilized to develop strong (strength ≤0.35 MPa) and stretchable (elongation ≤490%) structurally anisotropic hydrogel–organogel conjugates (HOCs) that display solvent-induced low-hysteresis bi-axial folding behavior and diverse folding patterns. The actuation stress (44 kPa) and response time (∼1 min) values of HOCs are comparable to that of selective naturally occurring systems. Moreover, the strategy allows us to control the orientation of the hydrogel segment in a parallel or orthogonal manner with respect to the principal plane (x-y) of the organogel film to realize the bi-axial folding patterns. Structurally anisotropic actuation systems possessing solvent-adaptable segment distribution ability have not been demonstrated before to the best of our knowledge. The generality of the approach is demonstrated by synthesizing different anisotropic HOCs based on various hydrogel and organogel segments. These HOCs hold promise in soft robotics, sensors, and biomedical applications.