Oriented calcite micropillars and prisms formed through aggregation and recrystallization of poly(acrylic acid) stabilized nanoparticles

Though calcium carbonate crystals with various morphologies have been successfully fabricated via bioinspired methods, the mechanism underlying crystallization of one-dimensional (1D) calcite microstructures along defined crystallographic axes is poorly understood. In this paper, we first show that by combining the effects of poly(acrylic acid) (PAA) and calcite substrates we can direct the formation of calcite through an intermediate complex of PAA and Ca²⁺ into oriented calcite micropillars with {104} faceted coaligned platelike subunits. Moreover, in situ AFM studies under different conditions than those used in bulk experiments also lead to formation of 1D calcite microstructures. With a slight change in conditions, arrays of oriented calcite prisms with triangular cross sections are formed on calcite substrates. Though distinct in morphology, these pillars and prisms form in a similar way via anisotropic nanoparticle aggregation, growth, fusion, and reorganization. The results may provide new insights into mechanisms of biomineralization.