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.

We detail the analysis of centrifugal homogenization process by a hydrodynamic model and the model-guided design of a low-cost centrifugal homogenizer. During operation, centrifugal force pushes a multiphase solution to be homogenized through a thin nozzle, consequently homogenizing its contents. We demonstrate and assess the homogenization of coarse emulsions into relatively monodisperse emulsions, as well as the application of centrifugal homogenization in the mechanical lysis of mpkCCD mouse kidney cells. To gain insight into the homogenization mechanism, we investigate the dependence of emulsion droplet size on geometrical parameters, centrifugal acceleration, and dispersed phase viscosity. Our experimental results are in qualitative agreement with models predicting the droplet size. Furthermore, they indicate that high shear rates kept constant throughout operation produce more monodisperse droplets. We show this ideal homogenization condition can be realized through hydrodynamic model-guided design minimizing transient effects inherent to centrifugal homogenization. Moreover, we achieved power densities comparable to commercial homogenizers by model guided optimization of homogenizer design and experimental conditions. Centrifugal homogenization using the proposed homogenizer design thus offers a low-cost alternative to existing technologies as it is constructed from off-the-shelf parts (Falcon tubes, syringe, needles) and used with a centrifuge, readily available in standard laboratory environment.

The bleaching efficacy of common bleaching agents and deionized water treated with non-thermal atmospheric pressure plasma in the pulp chamber for nonvital tooth bleaching was evaluated. A total of 120 extracted human maxillary first incisors were stained using human blood. Teeth were randomly divided into eight groups (n = 15). In the first four groups, teeth were bleached using 35% hydrogen peroxide gel, 37% carbamide peroxide gel, 2:1 (w/v) sodium perborate paste, and deionized water for 30 min. In the remaining groups, bleaching agents were treated with non-thermal atmospheric plasma for 5 min inside the pulp chamber. Overall color changes (∆E) were determined using Commission Internationale de L’Eclairage Lab Colour System. The plasma-assisted tooth bleaching has not increased tooth temperature beyond 37°C. Bleaching efficacies of bleaching agents were significantly improved when treated with non-thermal atmospheric plasma compared to their application (P < 0.05). A remarkable bleaching effect was obtained when bleaching agents were substituted with water and when treated with non-thermal atmospheric plasma. Non-thermal atmospheric plasma treatment could be a novel tool for activation of bleaching agents in the pulp chamber for nonvital tooth bleaching procedure. Moreover, water could be used as a novel bleaching agent when treated with the non-thermal atmospheric plasma to eliminate possible risks which might arise from peroxide-containing agents.