Biomedical Engineering Reference
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Fig. 3.4 ( a ) Time-dependent amount of free calcium ions measured in the solution ( blue )
using calcium ion selective electrode in comparison with dosed amount of calcium ions ( red ).
( b ) Schematic image of novel nucleation process through thermodynamically stable calcium
carbonate clusters in comparison with classical nucleation process (reproduced with permission
from [ 87 ]) (copyright 2008, American Association of Advancement of Science)
however, in a supersaturated solution, immediately before nucleation, clusters with
a radius of 1 nm were detected. Furthermore, while the incidence was low, the
existence of clusters with a radius of about 2 nm was also suggested.
Immediately after nucleation, the clusters further increased in size. There was
variation in the structure of the clusters, meaning that it was possible that these
different clusters ultimately formed different polymorphs of calcium carbonate—
i.e., calcite, vaterite, and aragonite—through the formation of amorphous phases
differing in structure (Fig. 3.4 b). This idea clearly differs from classical models,
which assume that the final crystal polymorph types are determined after nucleation.
In terms of the association between the macroscopic morphology of the produced
crystal and the growth unit, Banfield et al. suggested that natural biomineralization
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