Asymmetric microfiber actuators with reciprocal deformation

With the trend towards miniaturization in soft robotics, most microactuators encounter challenges in achieving versatile deformations. Here, we present an innovative microactuator design featuring reciprocal deformation, activated solely by humidity changes. These microactuators adopt an asymmetric microfiber configuration, characterized by a core–shell structure with a hydrophilic shell encapsulating hydrophobic microparticles. Utilizing droplet microfluidics for fabrication enables precise control over microfiber morphology and internal microparticles. During hygroscopic actuation, these microactuators undergo a unique two-stage deformation, exhibiting opposite trends in curvature variation—a stark departure from the unidirectional deformations observed in previous microactuators. The anisotropy inherent in asymmetric microfibers governs water absorption and desorption, driving this distinctive reciprocal deformation. These microactuators demonstrate versatility in controlled droplet transport and solid cargo manipulation, expanding their potential applications. This study not only unveils novel mechanisms but also broadens the functional spectrum of microactuator. © 2024 The Author(s).