Biomimetic Synthesis of Multilayered Aragonite Aggregates Using Alginate as Crystal Growth Modifier

Polysaccharides were believed to play an important role in the mineralization process of many organisms. As the source of continuously and uniformly releasing alginate molecules and Ca2+, alginate/Ca nanospherical gel was employed in the solution to induce the nucleation and growth of CaCO3. Time-resolved transmission electron microscopy (TEM) was applied to study the crystallization at a very early stage. It was found that the initially formed lens-like vaterite particles gradually dissolved from the middle of the particle and released alginate molecules and Ca2+ back into the system. As reaction time increased, the released substances were involved in the next stage of crystallization of CaCO3, in the form of needle-like and shuttle-like aragonite particles sequentially depending on the concentration of alginate molecules and Ca2+. Egg-box conformation of alginate and Ca2+ was considered a skeleton for the growth of such aragonite particles. Notably, shuttle-like aragonite particles were composed of bricks of several hundred nanometers in size, which were very similar to biogenetic nacreous layers in shells.