Hydrodynamic effects on calcium oxalate crystal growth kinetics probed by microfluidic chip platform

The effect of hydrodynamics on crystallization kinetics in confined flow systems (e.g., biological tubules) remains unclear. Herein, we developed a home-made microfluidic chip platform mimicking the curved, confined flow microenvironment of human renal tubules to investigate the growth kinetics and inhibition efficacy of calcium oxalate monohydrate (COM) crystals under controlled flow rates and constant supersaturation. Time-resolved imaging quantified COM growth rates at varied flow rates, identifying a transition from diffusion-controlled to reaction-controlled growth at 6 mL/h. COM growth is predominantly mediated by the screw-dislocation mechanism but shifts to 2D nucleation within the narrow supersaturation range of 1.8–2.1. The inhibition efficacy of polyphenols is regulated by the coupled effect of flow rate and concentration: decreasing flow rate either weakens or enhances inhibition depending on inhibitor concentration, with transition concentration thresholds varying among inhibitors and correlating with their crystal surface interaction strength. Simulations of pathological conditions showed reduced [Ca 2+ ]:[C 2 O 4 2− ] ratios diminish inhibitory efficacy via competitive adsorption between inhibitors and oxalate ions. However, ellagic acid outperforms citric and gallic acids, retaining over 95% inhibitory efficiency in high-calcium environments. This study highlights the key role of hydrodynamics and provides a theoretical basis for developing targeted, environment-adaptive strategies to prevent kidney stone formation.