Formation of Single-Crystalline Aragonite Tablets/Films via an Amorphous Precursor

Abstract

Thin tablets and films of calcium carbonate have been grown at the air-water interface via an amorphous precursor route using soluble process-directing agents and a Langmuir monolayer based on resorcarene. By using appropriate concentrations of poly(acrylic acid-sodium salt) in combination with Mg2+ ion, an initially amorphous film is deposited on the monolayer template, which subsequently crystallizes into a mosaic film composed of a mixture of single-crystalline and spherulitic patches of calcite and aragonite. Of particular importance is the synthesis of single-crystalline "tablets" of aragonite (approximately 600 nm thick), because this phase generally forms needle-like polycrystalline aggregates when grown in vitro. To our knowledge, a tabular single-crystalline morphology of aragonite has only been observed in the nacreous layer of mollusk shells. Therefore, this in vitro system may serve as a useful model for examining mechanistic issues pertinent to biomineralization, such as the influence of organic templates on nucleation from an amorphous phase.

Amorphous Phase Mediated Crystallization: Fundamentals of Biomineralization

“…Amorphous calcium carbonate (ACC) is the precursor phase for many invertebrate biomineralizations, such as in the formation of sea urchins [35,36], mollusk shells [23,[37][38][39], and coral skeletons [40]. The transformation of amorphous phases to crystalline phases (Table 1) can occur via several crystallization pathways [21,24,[41][42][43][44][45], such as surface-mediated heterogeneous nucleation [11,[46][47][48], dissolution/re-precipitation [49][50][51][52][53][54][55][56], and solid-solid phase transformation (structure reorganization) [19,33,[57][58][59][60][61][62]. The transformation mechanism and crystallization kinetics depend vitally on the detailed crystallization pathway and on the solution environment [52].…”

“…In the absence of the organic matrix, polyelectrolytes can also guide the formation of various hierarchically structured CaP and CaC crystals. Gower and co-workers have fabricated a variety of non-equilibrium (i.e., non-faceted) morphologies of minerals by using PILP as the precursor, including crystal drops [21], thin films/tablets [62,140,141], and fibers [142,143]. With the help of polyelectrolytes, Cölfen and co-workers have made varied CaC mesocrystals (superstructured nanocrystals with a common crystallographic orientation) (see the review of mesocrystals in biominerals [144]).…”

Biomimetic synthesis of calcite films by a polymer-induced liquid-precursor (PILP) process

“…The overall effect of adding these minute quantities of polymer is that it transforms the solution crystallization into a solidification process, in which non-equilibrium crystal morphologies are generated because the crystals retain the shape of the precursor. The formation of thin mineral tablets and films [34][35][36], as well as the ability to ''mold'' and shape crystals [37][38][39], are characteristics of biologically formed minerals, thus we have proposed the PILP process may play a fundamental role in natural biomineralization.…”

Usage of polymer brushes as substrates of bone cells

“…The skeletal calcium carbonate hard part forms in this organism through an amorphous precursor phase. ACC as a transient precusor could be observed also in vitro to produce microstructured single-calcite crystals [59,60] or aragonite tablets [61].…”