Slug-flow microchannel enables efficient and controllable preparation of sensitive protein nanoparticles

Microreactors are valued for efficient mixing and precise control in nanoparticle synthesis. However, when encapsulating sensitive proteins and enzymes, conventional fluidic shear causes serious damage and activity loss. Critically, the interplay between mixing performance and shear effects within microreactors remains poorly understood, yet is pivotal for the successful preparation of protein-based nanoparticles. This study applied a gas-liquid slug-flow microchannel to synthesize protein nanostructures and enzyme nanocapsules, compared to the single-phase flow microchannel, microstructured continuous stirred-tank reactor (micro-CSTR), and batch reactor. Mixing, residence time distribution, and shear effects in these reactors were examined via experiments and computational fluid dynamics (CFD) simulations, linking them to the properties of prepared protein nanoparticles. Results show that the slug-flow microchannel provides efficient mixing, narrow residence time distribution, and suitable shear. This combination offers significant advantages for the uniformity of particle size distribution, drug release, enzyme activity, and stability in both the thermodynamically driven self-assembly of nanoparticles and kinetically driven synthesis of nanocapsules. Specifically, for catalase nanocapsules, this strategy achieved a low PDI of 0.165 (vs. 0.3-0.5 in references) and a productivity of 4 g·day^-1, equivalent to 100 lab-scale batch reactors. This demonstrates the strategy's strong potential for industrial-scale production and biomedical application of precious protein nanoparticles.