Bioinspired self-coiling Janus microfiber actuators for micro-lifter and humidity sensing

Many soft coiled actuators are mimic the desirable structures of plant tendril. Here, we present a facile microfluidic spinning method to fabricate self-coiling Janus microfiber actuator with tunable morphology, spontaneous coiling performance and reversible traction property. By adjusting the component of hydrogel Janus fiber in a microfluidic spinning device with theta-shaped channels, tens of hundreds of homogeneous coils can be spontaneously and rapidly generated due to asymmetric contraction upon dehydration process, and three different forms of coiled fibers with various screw diameters are presented. Furthermore, the coiled Janus microfiber with hygroscopic properties possesses a reversible coiling/uncoiling performance under humidity gradients, which can serve as a micro-actuator to lift a certain weight with enough tensile strain and long-range tractive displacement. In addition, local reversible coiling/uncoiling morphing is achieved under water contact and near infrared light optothermal stimulations. As a verification of this coiled microfiber actuator, a smart switch is designed to control different colored LED lights for sensing an ambient moisture content.