Fast prototyping using 3D printed templates and flexible fluoropolymer microcapillary films offers enhanced micromixing in immobilised (bio)catalytic reactions

Microreactors offer large surface-area-to-volume (SAV) ratios and short diffusion distances, yet, even at sub-millimetre space, there remains a level of mass transfer control of reactions. This can be minimised using passive micromixers currently requiring access to advanced microfabrication techniques. We report the fast fabrication and in-depth micromixing characterisation of inexpensive non-linear microstructure prototypes using, for the first time, a flexible fluoropolymer microcapillary film (MCF) re-shaped, post-extrusion, with 3D printed templates offering in-flow enhancement of mass transfer in immobilised (bio)catalytic reactions not previously studied for this type of micro-engineered material. The versatile “push-and-click” 3D printed templates allow one-step production of multi-bored, non-invasive micromixers with simple architectures, namely ‘square’, ‘zigzag’ and ‘wavy’ geometries without the limitations of conventional microfluidic devices. The passive micromixers were numerically evaluated using Computational Fluid Dynamics (CFDs) and extensively validated experimentally using novel Residence time distribution (RTD) data which assessed the role of Reynold numbers (0.6 – 60) and molecular diffusion coefficients (10⁻⁶ –10⁻¹¹ m²/s), providing significant in-depth understanding of fluid flow distribution. By evaluating the in-flow oxidative coupling reaction of o-phenylenediamine (OPD, a chromogenic substrate) to 2,3-diaminophenazine (DAP) with an immobilised enzyme, horseradish peroxidase (HRP), we demonstrated the reaction rates in the ‘square’ and ‘zigzag’ (sharp bends) were improved by ∼43 and ∼46% respectively, compared to straight microcapillaries. This is linked to enhanced radial fluid movement. The proposed prototypes can be readily tailored for facilitated fabrication of practical high-performance microreactors suited for heterogeneous assays or in-flow (bio)catalytic reactions in non-microdevice dedicated labs.