Solute convection during the whole process of protein crystal growth

We numerically simulated sedimentation flow and buoyancy-driven convection during protein crystal growth in which the crystal size changes from 0.1 to 100 μm and clarified how gravitational fields affect the various stages of crystal growth. When the crystal size is below a few μm, most crystals are suspended in solution and solute transport near the crystal is mainly limited by diffusive transport. When the crystal size is above a few μm, sedimentation flow dominates near the crystal, but solute transport is still mainly limited to diffusive transport. When crystals grow to several μm, most of them settle to the bottom and continue to grow there. When the size is above several 10 μm, buoyancy-driven convection dominates solute transport near growing crystals at the bottom, and the contribution from buoyancy induced convection to crystal interfacial growth rate appears on Earth in comparison with that under zero-gravity condition and increases with increasing crystal size. During the whole crystal growth process, the crystal interface growth rate shows the tendency to decrease as the crystal grows under both normal and zero-gravity conditions. Moreover, our simulations of crystal sedimentation are consistent with experimental observations of lysozyme crystallization that most crystals settle to the bottom when their size reaches several μm.