Nucleation kinetics of calcium oxalate monohydrate as a function of pH, magnesium, and osteopontin concentration quantified with droplet microfluidics

Abstract

A droplet-based microfluidic platform is presented to study the nucleation kinetics of calcium oxalate monohydrate (COM), the most common constituent of kidney stones, while carefully monitoring the pseudo-polymorphic transitions. The precipitation kinetics of COM is studied as a function of supersaturation and pH as well as in the presence of inhibitors of stone formation, magnesium ions (Mg2+), and osteopontin (OPN). We rationalize the trends observed in the measured nucleation rates leveraging a solution chemistry model validated using isothermal solubility measurements. In equimolar calcium and oxalate ion concentrations with different buffer solutions, dramatically slower kinetics is observed at pH 6.0 compared to pHs 3.6 and 8.6. The addition of both Mg2+ and OPN to the solution slows down kinetics appreciably. Interestingly, complete nucleation inhibition is observed at significantly lower OPN, namely, 3.2 × 10−8 M, than Mg2+ concentrations, 0.875 × 10−4 M. The observed inhibition effect of OPN emphasizes the often-overlooked role of macromolecules on COM nucleation due to their low concentration presence in urine. Moreover, analysis of growth rates calculated from observed lag times suggests that inhibition in the presence of Mg2+ cannot be explained solely on altered supersaturation. The presented study highlights the potential of microfluidics in overcoming a major challenge in nephrolithiasis research, the overwhelming physiochemical complexity of urine.

Sex disparities and the risk of urolithiasis: a large cross-sectional study

“…Fatma et al. demonstrated that nucleation kinetics of calcium oxalate monohydrate was dramatically slower at pH 6.0 compared to pH 3.6 and pH 8.6 [ 32 ]. In our participants, the mean UpH was around 6.0 and a higher pH could be a risk factor for urolithiasis.…”

Role of Hyaluronic Acid on the Nucleation Kinetics of Calcium Oxalate Hydrates in Artificial Urine Quantified with Droplet Microfluidics

“…Three sections of the microfluidic device, namely, droplet formation, mixing, and storage & observation zones, are depicted in Figure 1b. A more detailed description of the microfluidic chip design and the optimization of the chip geometry is given in Ibis et al 88 and in the S.1 section in the SI. To acquire statistically significant nucleation kinetics measurements of COM and COD under understudied conditions, both the induction time, the first moment a crystal is observed, and the pseudo-polymorphic form of the crystal are identified.…”

“…The mold was then hydrophobized to minimize the PDMS adhesion. Uncured PDMS is poured into the mold, and the PDMS is cured for 24 h as described previously by Ibis et al 88 The cured PDMS is peeled from the mold to release the top PDMS section of the chip. The inlet and exit holes are prepared with a biopsy punch.…”

“…The microfluidic chip is produced by a soft lithography. ,,, The mold used in soft lithography was designed in SolidWorks, and then it is printed with a 3D printed (EnvisionTEC Micro Plus Hi-Res - 43 × 27mm). The mold was then hydrophobized to minimize the PDMS adhesion.…”

Molecular Mechanism of Organic Crystal Nucleation: A Perspective of Solution Chemistry and Polymorphism

“…A number of experimental techniques for measuring crystal nucleation rates have become available nowadays, such as the double-pulse technique [118,119], microfluidics [120,121], and the high-throughput setup [122,123]. These analytical techniques produce a large number of nucleation kinetics data.…”