Monolithic 3D-printed split-and-recombine micromixer integrated into a microfluidic concentration gradient generator

Efficient micromixing in enclosed microchannels is essential for reliable lab-on-a-chip operation but typically requires planar or multilayer soft-lithographic fabrication, limiting geometric freedom and increasing production complexity. Here, we report a fully monolithic split-and-recombine (SAR) micromixer fabricated in a single step using stereolithography digital light processing (SLA-DLP), eliminating molds, bonding, and cleanroom processing. The three-dimensional SAR architecture systematically divides, reorients, and recombines fluid streams, enabling high mixing performance over a wide range of operating conditions. Computational fluid dynamics simulations and experimental validation show excellent agreement, achieving mixing efficiencies above 0.90 across Reynolds numbers from 0.1 to 100. Leveraging its compact and robust performance, the micromixer was integrated into a five-output microfluidic concentration gradient generator, which produced stable and reproducible concentration profiles for both fluorescent tracers and protein solutions. The complete device, including microchannels and functional fluidic features, was printed in under 1.5 h using a standard desktop SLA-DLP system. These results demonstrate that additive manufacturing can deliver high-performance micromixing capabilities, establishing a rapid, accessible, and fully digital route for the fabrication of advanced microfluidic systems.