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

A new class of molecular modifiers, i.e. natural polyphenols, inspired from Chinese tea has been discovered for CaOx crystallization inhibition. These polyphenol modifiers display a unique dual action of growth promoter and inhibitor dependent upon their concentrations. The unexpected, remarkable growth promotion reaches a new record up to 75%, leading to the formation of macroscopic crystal whiskers by change in growth mode from spiral-mediated to generation of 2D islands and layer spreading mechanism and concurrent growth of step bunches (not seen commonly). • Calcium oxalate crystal whiskers were induced by natural polyphenols on COM (0 1 0) surfaces. • Step growth mode was changed from spiral dislocation to 2D layer growth. • Adsorbed polyphenols on surface inhibited step advancement and induced the formation of step bunches. • The governing regime of whisker formation is determined by inhibitors concentration and supersaturation. 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.