Control of Calcium Carbonate Crystallization in an Orthogonal Diffusion System

Crystallization in living organisms is highly regulated by both passive diffusion and active transport across the cellular membrane or plasm. There have been studies that mimic slow diffusion in a biological system to control crystallization using microfluidic devices and diffusion-limiting media. This study introduced an orthogonal diffusion system in which the outer calcium and carbonate ions were perpendicularly diffused into a hydrogel. This orthogonal setup opens up a new possibility in designing and engineering crystalline materials than traditional techniques utilizing collinear orthogonal diffusion fluxes of the reagents. Various microenvironments could be formed two-dimensionally in a hydrogel according to the ion flux and calcium to carbonate ratio in an orthogonal diffusion system. Through this, it was possible to systematically investigate the effect of different levels of ion flux and ratio on crystallization. Different ion fluxes and ratios resulted in different morphologies of calcium carbonate, such as otoconia-, rhombohedron-, rosette-, and sphere-shaped calcites. In addition, the crystallization process is supported by a numerical simulation.