Dual Mechanism of Natural Polyphenols on crystal whiskers formation on calcium oxalate monohydrate crystal surface

Designing (macro)molecules controlling crystallization is an essential approach to regulate structure and properties of crystalline materials and circumvent detrimental mineralization in nature, biological, and synthetic systems. Here we discovered four novel, natural polyphenols, including gallic acid, ellagic acid, punicalagin, and tannic acid, as a new class of inhibitors for nucleation and crystal growth of calcium oxalate (CaOx), a primary constitution of kidney stones. Study of time-resolved growth reveals that polyphenols regulate the kinetics of crystal-liquid interface acting as a dual role of growth promoter and inhibitor which displays a new record of growth promotion up to 75% or complete suppression, dependent upon the modifier concentration. Time-elapsed in situ atomic force microscopy measurements unveil these modifiers regulate the growth mode from spiral-mediated to generation of two-dimensional (2D) islands and layer spreading mechanism, leading to formation of step bunches growing out of (0   1   0) surface and forming macroscopically crystal whiskers. The governing regime between growth promotion and inhibition is determined by inhibitors concentration but can be influenced by crystallization driving force. Such unique growth mechanism of crystal whiskers may also provide potential implications for understanding and synthesizing branched and hierarchical structures of biomimetic materials.