Controllable Fabrication of Functional Microhelices with Droplet Microfluidics.

Microhelices with unique three-dimensional (3D) helical structures have attracted great attention due to applications in various fields, especially magnetic microhelices can be applied as microrobots for removal of clogging substance in microchannels, cargo transport, cell manipulation, and so on. Here, a facile and flexible strategy is developed to controllably fabricate microhelices with droplet microfluidics. On-flow fabrication of microhelices is simply achieved by generating monodisperse droplets first, transforming the spherical droplets into helical templates subsequently due to the liquid rope coiling effect, followed by polymerizing monomers in the templates via on-line UV irradiation and then degrading the shells of helical fibers. Benefitting from the flexible controllability of microfluidics, the morphologies of microhelices can be precisely controlled by adjusting the flow rates of fluids and the structures of microfluidic devices. Functional microhelices can be easily prepared by introducing functional components or elements into inner fluids. By introducing magnetic nanoparticles into inner fluids, magnetic microhelices are easily fabricated as microrobots that featured with magnetic-field-driven corkscrew-like motion for efficient cargo transport and removal of clogging substance in microchannels. This novel microfabrication method allows a precise morphological control and easy functionalization of microhelices, providing a flexible and versatile strategy for fabricating designer functional microhelices for diverse applications.