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.
Lab‐On‐A‐Chips promise solutions for high throughput and specific analysis for environmental and health applications, with the challenge to develop materials allowing fast, easy, and cheap microfabrication and efficient surface treatment. Cyclic olefin copolymer (COC) is a promising thermoplastic, easily microfabricated for both rapid prototyping and low‐cost mass production of microfluidic devices but still needing efficient surface modification strategies. This study reports for the first time the optimization of an easy COC silica coating process by plasma‐enhanced chemical vapor deposition at atmospheric pressure with plasma jet and tetraethylorthosilicate as precursor, leading to a 158 ± 7 nm thickness and a 14‐day‐stability of hydrophilic properties for a COC‐embedded microchannel (100 µm), paving the way for a simplified and controlled COC surface modification.
Off-stoichiometry thiol-ene polymer (OSTE) is an emerging thermoset with interesting properties for the development of lab-on-a-chip (LOAC), such as easy microfabrication process, suitable surface chemistry for modification and UV-transparency. One of the challenges for LOAC development is the integration of all the analytical steps in one microchannel, and particularly, trace level analytes extraction/preconcentration steps. In this study, two strategies for the immobilization of efficient tools for this purpose, thiol-modified (C3-SH) aptamers, on OSTE polymer surfaces were developed and compared. The first approach relies on a direct UV-initiated click chemistry reaction to graft thiol-terminated aptamers on ene-terminated OSTE surfaces. The second strategy consists of the immobilization of thiol-terminated aptamers onto OSTE substrates covered by gold nanoparticles. The presence of an intermediate gold nanoparticle layer on OSTE has shown great interest in the efficient immobilization of aptamers, preserving their interaction with the target, and preventing non-specific adsorption. With this second innovative strategy, we proved, for the first time the concept of creating multiple functional zones for sample treatment in an open OSTE-microchannel thanks to the immobilization of aptamers in consecutive areas by the simple droplet deposition methodology. This methodological development allows further consideration of OSTE material for lab-on-a-chip designs, integrating multiple zones for sample pretreatment, based on molecular recognition by ligands, such as aptamers, in a specific zone of the microchannel and is adaptable to a large range of analytical applications for LOAC industrialization.
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