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Nephrolithiasis is a major health concern in western countries. Herein, we propose a microfluidic based approach to mimic the physical and physicochemical conditions encountered in the collecting duct in a nephron where calcium oxalate (CaOx) precipitation occurs. Our objective is to understand the parameters involved in the formation of such crystals. The microfluidic platform is reversible, allowing interfacial characterizations using scanning electron microscopy imaging and Raman spectroscopy. CaOx crystalline phases and morphologies were studied with respect to hydrodynamics and physicochemical conditions within the channel and at the outlet. While calcium oxalate monohydrate (COM) crystals were dominant within the channel, at the outlet, the crystals were calcium oxalate dihydrate (COD) crystals, which agrees with medical observations. Decreasing the flow rate lowered down the induction time for CaOx formation and enhanced the occurrence of COD crystals. The kinetics of COM crystals growth studied in situ showed two regimes, an initial surface-limited reaction, followed by a transport-limited growth with a dependency of the kinetics on the position of the crystal in the channel. Numerical modeling of CaOx formation in a microchannel using an in-house model considering the chemical reactions involved allowed to confirm the experimental observations on the location of precipitate formation but also to quantitatively match the scaling law related to the early growth of precipitate particles. Finally, the effect of polyphenols naturally found in green tea (GT) on modulating CaOx crystallization was studied in the microfluidic device in different scenarios where GT was initially mixed in solution with the Ca and/or the Ox precursors. The formation of COD crystals rather than COM ones was always predominant; however, depending on the conditions, CaOx crystals of different morphologies could be observed, including COD crystals with an elongated (100) crystalline face and COM crystals with a round-shaped morphology with a concave crystalline face.

Quasiclassical trajectory computations are performed for the F – + CH 3 I( v = 0, JK ) → I – + CH 3 F (S N 2) and HF + CH 2 I – (proton-transfer) reactions considering initial rotational states characterized by J = {0, 2, 4, 6, 8, 12, and 16} and K = {0 and J } in the 1–30 kcal/mol collision energy ( E coll ) range. Tumbling rotation ( K = 0) counteracts orientation effects, thereby hindering the S N 2 reactivity by about 15% for J = 16 in the 1–15 kcal/mol E coll range and has a negligible effect on proton transfer. Spinning about the C–I bond ( K = J ), which is 21 times faster than tumbling, makes the reactions more direct, inhibiting the S N 2 reactivity by 25% in some cases, whereas significantly enhancing the proton-transfer channel by a factor of 2 at E coll = 15 kcal/mol due to the fact that the spinning-induced centrifugal force hinders complex formation by breaking H-bonds and activates C–H bond cleavage, thereby promoting proton abstraction on the expense of substitution. At higher E coll , as the reactions become more direct, the rotational effects are diminishing.

The evolution of different confined precipitation patterns is determined by the ratio of the chemical and hydrodynamic time scales.

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Controlling self-organization in precipitation reactions has received growing attention in the efforts of engineering highly ordered spatial structures. Experiments have been successful in regulating the band patterns of the Liesegang phenomenon on various scales. Herein we show that by adjusting the composition of the hydrogel medium we can switch the final pattern between the classical band structure and the rare precipitate spots with hexagonal symmetry. The accompanying modeling study reveals that besides the modification of gel property, the tuning of the time scale of diffusional spreading of hydroxide ion with respect to that of the phase separation drives the mode selection between one-dimensional band and two-dimensional spot patterns.

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