Polymerization-induced phase separation fabrication: A versatile microfluidic technique to prepare microfibers with various cross sectional shapes and structures

Shaped microfibers have attracted great interests because of their broad applications. However, their preparation by microfluidic technique needs multi-phases by careful and accurate control of multi-flows. Here, we develop a simple polymerization-induced phase separation (PIPS) technique to fabricate microfibers with various cross-section shapes and structures. PIPS occurs when we transfer a single-phase flow of polyethylene glycol/acrylamide (PEG/AM) solution into a microchannel which is heated to initiate the polymerization of AM. This results in the formation of a polyacrylamide (PAM) core and a PEG solution layer between the microchannel wall and the core, thus facilitating the smooth spinning of the fibers and avoiding clogging of the microchannels. We designate microchannels with different shaped cross-sections to prepare PAM fibers which duplicate the shapes of the microchannels. In addition, we prepare fiber-in-tube fibers and biomimic fiber-in-matrice hybrid structures in the center of aligned capillaries. We use different acrylate monomers to prepare each fiber in the multiple-fibers, yielding fibers with stimulus responses. Further, each fiber can be functionalized by simple adding functional materials in the precursor solutions. This technique uses only a single phase solution and designated microchannels, providing a simple route to produce structured fibers with tailored shape and chemistry.