Solution rheological parameters modulate calcium phosphate mineralization in a microfluidic device.

Mineralization of calcium phosphate and other materials in vivo and in natural water sources occurs in solutions that are not stagnant, but are flowing. Flow conditions could influence solution mixing and, therefore, mineralization kinetics or mechanism. This work describes the design and characterization of a multi-stream parallel flow microfluidic device that allows for controlled solution mixing and indirect control of laminar flow by altering the microfluidic device width, shape, length, flow rate, and flow velocity. Measurement of solution mixing was accomplished using the protonation of quinine to produce a fluorescent molecule and the rate of calcium phosphate mineralization was monitored by optical microscopy and analysis with Image J software. Experiments were designed to hold the flow rate constant, allowing the solution velocity to vary and to hold the velocity constant, allowing the flow rate to vary. It was found that small changes in laminar flow conditions do not correlate to mineral growth, but solution velocity and flow rate have a substantial effect on calcium phosphate mineralization. AFM and SEM characterization of the mineral produced shows an amorphous material and varying degrees of mineralization possibly due to variation in supersaturation conditions across the solution mixing area. This microfluidic device and analysis procedure allows for improved study of mineralization and the effect of flow conditions relevant to those seen in biological settings.