Programmable Twisted Microchannels in Polymer Fibers via Rotational Thermal Drawing for Enhanced Micromixing.

Micromixers are essential components of microfluidic systems, enabling rapid and homogeneous mixing at microliter and submicroliter scales. Although three-dimensional (3D) microchannel geometries can significantly enhance mixing performance, their broader adoption has been limited by fabrication challenges that restrict geometric control, scalability, and system integration. Here, we report an in-fiber twisted micromixer, termed the Fiber-μMixer, fabricated by rotational thermal drawing (rTDP). By introducing controlled rotation and revolution during drawing, this method enables scalable fabrication of microchannels with centered and off-centered geometries, feature sizes down to 100 μm, and twist pitches as small as 4 mm. The resulting twisted and helical channel architectures enhance microscale mixing through the combined effects of swirl-induced advection and Dean-vortex-driven secondary flows. Numerical simulations and experiments demonstrate strong mixing performance across a range of Reynolds numbers, with mixing efficiencies exceeding 75% and negligible pressure penalty in the intermediate regime (1 ≤ Re ≤ 30), where conventional passive micromixers typically underperform. This in-fiber micromixing platform provides a practical and scalable route toward compact, flexible, and multifunctional microfluidic systems, opening opportunities for lab-in-fiber technologies and advanced microscale fluid handling.