Oriented Calcite Micropillars and Prisms Formed through Aggregation and Recrystallization of Poly(Acrylic Acid) Stabilized Nanoparticles

Abstract

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 Ca 2+ 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.

Amorphous Phase Mediated Crystallization: Fundamentals of Biomineralization

“…A mesocrystal can be obtained by the oriented attachment of crystalline precursors [16,[145][146][147]. However, the amorphous phase or poorly crystalline particles can also be the precursor phase for forming mesocrystals [148][149][150]. It should be noted that the exact crystallization pathway cannot be judged only by the mineral morphologies [14].…”

“…CCT assumes monomer addition during the crystal nucleation and the crystal growth processes. However, other crystallization pathways might happen in biomimetic mineralization systems [14], such as prenucleation clusters [17][18][19][20]166], amorphous phase mediated crystallization, and aggregation-based crystallization [16,[145][146][147][148][149][150]. For these non-classical crystallization pathways, many unexpected crystallization behaviors have been reported, such as faster nucleation of HAP at lower pH with lower supersaturation [10] and the formation of abnormally high Mg-calcite [132].…”

Anisotropic nanowire growth via a self-confined amorphous template process: A reconsideration on the role of amorphous calcium carbonate

“…Moreover, ACC emerges frequently in the formation of CaCO 3 fibers [24,28,34,38,39]. Accordingly, in immature nanowires, we found an ACC layer (Figs.…”

“…The stabilization and transformation of the ACC phase has been studied [31][32][33][34][35][36][37][38][39][40][41]. Gower et al proposed a so-called polymer induced liquid precursor (PILP) process which has been found in many mineralization processes where polymers were used as stabilizers [10,31].…”

“…According to their observations, the wick effect, which was proposed for the vapor-liquid-solid process of other kinds of nanowires [42], could explain the anisotropic growth of CaCO 3 nanowires [10]. Qi et al reported the growth of calcite micropillars through the assembly of polymer-stabilized nanoparticles into pure amorphous precursor nanofibers that then crystallized into the calcite form [38]. They suggested that the anisotropic growth was induced by the dipole-dipole effect or the fusion of the nanoparticles.…”