Theory of competitive adsorption-nucleation in polypeptide-mediated biomineralization

The process of biomineralization occurs in various natural organisms with astonishing ease by the interplay between polymers and mineralization but eludes a fundamental understanding. In addressing how specific polymers direct selection of mineral morphologies and their growth kinetics, we present a new model based on a competition between adsorption of polymers onto selective interfaces and nucleation growth of minerals. The model is couched in the context of zinc oxide, crystallized from solutions containing polypeptides, where systematic experimental data are available. Adsorption of the polymer onto certain crystallographic planes leads to poisoning of the surfaces, and as a result these surfaces are arrested from further growth. By this mechanism, originally disfavored growth sectors are promoted to grow by suppressing the initial faster growing sectors. Our theory predicts the relative growth rates of different sectors altered by selective adsorption of polymers. Theoretical prediction of the dependence of the aspect ratio on polypeptide concentration is in agreement with experimental results, providing credence to the applicability of adsorption-nucleation models to polymer-mediated biomineralization.