One-step fabrication of moon-shaped microrobots through in situ solidification of magnetic Janus droplets in microchannels

Special-shaped microscale structures have shed light on new possibilities in key fields of chemistry, medicine, and energy. Asymmetrical microrobots with sensitive magnetic responses can be useful tools in controlled chemical reactions, drug delivery, and functional material synthesis. Microfluidic-based emulsion generation technology is adopted as a powerful platform for the fabrication of steerable microrobots with refined control. Specifically, Janus droplets are generated in microfluidic chips featuring a flow-focusing configuration. Asymmetrical morphologies of the Janus droplets are achieved by balancing the interfacial tensions, where the portion containing magnetic nanoparticles is solidified through the UV-initiated polymerization process right after the formation while the Janus structure is left intact. We succeed in controlling the morphology of the Janus droplet along with the moon-shaped robots hydrodynamically and applying them in flow control at the microscale under external magnetic fields, which are characterized and quantified by three-dimensional profile measurement and high-speed microparticle velocimetry measurement. Our proposed on-chip fabrication method using a microfluidic platform not only provides a method for fabricating magnetic robots but also enables tuning the complex morphologies and functionalities at the microscale, which could shed light on new possibilities in key fields of controlled chemistry reaction, medicine synthesis, and energy generation.