Magnetic Janus origami robot for cross-scale droplet omni-manipulation

In Situ Multi-Directional Liquid Manipulation Enabled by 3D Asymmetric Fang-Structured Surface

Decorating surfaces with wetting gradients or topological structures is a prevailing strategy to control uni-directional spreading without energy input. However, current methods, limited by fixed design, cannot achieve multi-directional control of liquids, posing challenges to practical applications. Here, a structured surface composed of arrayed three-dimensional asymmetric fang-structured units is reported that enable in situ control of customized multi-directional spreading for different surface tension liquids, exhibiting five novel modes. This is attributed to bottom-up distributed multi-curvature features of surface units, which create varied Laplace pressure gradients to guide the spreading of different-wettability liquids along specific directions. The surface's capability to respond to liquid properties for multimodal control leads to innovative functions that are absent in conventional structured surfaces. Selective multi-path circuits can be constructed by taking advantage of rich liquid behaviors with the surface; surface tensions of wetting liquids can be portably indicated with a resolution scope of 0.3-3.4 mN m-1 using the surface; temperature-mediated change of liquid properties is utilized to smartly manipulate liquid behavior and achieve the spatiotemporal-controllable targeted cooling of the surface at its heated state. These novel applications open new avenues for developing advanced surfaces for liquid manipulation.

Magnetic-actuated hydrogel microrobots with multimodal motion and collective behavior

Magnetic-actuated miniature robots have sparked growing interest owing to their promising potential in biomedical applications, such as noninvasive diagnosis, cargo delivery, and microsurgery. Innovations are required to combine biodegradable materials with flexible mobility to promote the translation of magnetic robots towards in vivo application. This study proposes a biodegradable magnetic hydrogel robot (MHR) with multimodal locomotion and collective behavior through magnetic-assisted fabrication. The MHRs with aligned magnetic chains inside their structures have more significant maximum motion speeds under rotating magnetic fields than the robots without magnetic alignment. By reconfiguring the external magnetic fields, three types of stable motion modes (tumbling, spinning, and wobbling modes) of the individual MHRs can be triggered, while flexible conversion can be achieved between each motion mode. The motion mechanism of each motion mode under diverse rotating magnetic fields has been analyzed. The collective behavior of the MHRs, which is triggered by the magnetic dipole force, can enhance the motion performance and pass through sophisticated terrains. Furthermore, the experimental results demonstrate that the assembled MHRs can execute complicated tasks such as targeted cargo delivery. The proposed MHRs with multimodal locomotion and assembled behavior show effective motion efficiency, flexible maneuverability, and remarkable targeting ability, providing a new choice for magnetic robots in biomedical applications.

Infinite Self-Propulsion of Circularly On/Discharged Droplets

Self-propulsion of droplets in a controlled and long path at a high-speed is crucial for organic synthesis, pathological diagnosis and programable lab-on-a-chip. To date, extensive efforts have been made to achieve droplet self-propulsion by asymmetric gradient, yet, existing structural, chemical, or charge density gradients can only last for a while (<50 mm). Here, this work designs a symmetrical waved alternating potential (WAP) on a superhydrophobic surface to charge or discharge the droplets during the transport process. By deeply studying the motion mechanisms for neutral droplets and charged droplets, the circularly on/discharged droplets achieve the infinite self-propulsion (>1000 mm) with an ultrahigh velocity of meters per second. In addition, after permutation and combination of two motion styles of the droplets, it can be competent for more interesting work, such as liquid diode and liquid logic gate. Being assembled into a microfluidic chip, the strategy would be applied in chemical synthesis, cell culture, and diagnostic kits.