Spatiotemporal Distribution of Calcium Oxalate Crystals in a Microchannel

The formation of crystals under physicochemical and flow dynamic conditions in constrained dimensions is ubiquitous in nature and of great interest to different disciplines in science. In this report, using a physicochemical approach, we investigated the spatiotemporal precipitation of calcium oxalate (CaOx) crystals, the most common chemical compound found in kidney stones, at the dynamic interface generated by the interdiffusion of oxalate and calcium ions in a microchannel. Spatiotemporal crystal habit distributions were mapped and analyzed using scanning electron microscopy, and their formation was correlated to a numerical model that accounts for supersaturation and gravity. We show that while monohydrated CaOx crystals are the most frequent with random distribution in the channel, the dihydrated CaOx phase crystals are mainly formed at the contact line between oxalate and calcium at the oxalate side, where gradients are large and supersaturation is low. In addition, the size of the crystals correlates well with the supersaturation with increasing monodispersity over time. These results are supported by the numerical model. The simulations also show that nucleation can occur everywhere in the channel; however, with time, nucleation is limited to the upper level of the channel, while crystals on the bottom continue to grow from the reactants.