Multi-stimuli responsive and reversible soft actuator engineered by layered fibrous matrix and hydrogel micropatterns

Soft actuators enable the motion of soft materials such as living organisms, biomaterials, and flexible materials in environments where multiple stimuli are simultaneously present. Although various fast, reversible, and direction-guided actuators exist, their material and structural complexity hinder the construction of a simple fabrication platform for actuators responsive to various environmental conditions with reversible and controlled actuation dynamics. We propose an engineered multi-responsive actuator fabrication platform by combining electrospinning and hydrogel lithography techniques. The fabricated soft actuator is composed of stimuli-responsive hydrogel fibers as an active layer, non-responsive fibers as a passive layer, and a micropatterned hydrogel coupling layer to combine those layers. We demonstrate the reversible bending and unbending of the actuator in response to changes in pH and temperature for less than 2 min. The computational modeling is used to elucidate the bending mechanism of the layered actuator and obtain the key parameters to determine its characteristics. The bending direction is regulated by modulating the mechanical properties of the actuator materials and dimensions of hydrogel micropatterns. The fabrication process is versatile and multi-responsive actuation is achieved by adding another active fiber layer without modifying it. Our study provides an insight into the design of a stimulus-specific, multi-scale, multi-functional soft actuator.