also found that Mg
2+ combination could defer ACC transformation for the most
part, and such effect improved with the increase of Mg
2+ amount.
In biomineralization processes, the formation of inorganic crystals is controlled
by organic macromolecules such as proteins ((Mann 1996); (Addadi & Weiner
1985)). Collagen is the most important water-insoluble fibrin which represents the
framework of extracellular matrix. The basic structure of collagen is tropocollagen,
and its primary structure has a repetitive sequence of (Gly-x-y) n , of which x usually
represent Pro, and y of Hy-Pro of Hy-Lys. Shen et al. (2002) studied collagenmediated calcium carbonate crystal in vitro in order to reveal the principle of
protein-mediated mineralization process. The results of XRD and SEM of calcium
carbonate crystal deposition showed that only calcite was formed, and the calcite
growth is more and more inhibited as collagen is increased in concentration
(Fig. 6.17). It means that collagen does not change the polymorph of calcium
carbonates. With the increasing concentration of collagen, the morphology of calcite
changed from perfect rhombohedral to well-faceted rhombohedral crystals with
little disfigurement, and then to overgrown calcite crystals with new planes. The
thickness of new layers became thinner with the increasing of collagen, some of
calcite crystal planes would develop into a flowerlike form, and they become
spherulites as the concentration further increases (>10 g/l). They provided an
explanation, why collagen would absorb on the edges of {1 0 4} planes of calcite,
which are parallel to the c-axis, and inhibited its growth, thus new planes appeared.
The new planes started to appear at the edges of rhombohedral calcite crystals when
collagen was present in the solution, since crystal growth starts at edges and corners,
which provided good attachment sites; it led to the decrease of growth rate and new
plane growth on such positions. New planes formed have better attraction for
collagen, which would eventually alternate the morphologies. Collagen additives
not only influenced morphology of the crystals, but also the quantity. Number of
crystals increased, while size diminished with the increase of the protein concentration. The adsorption of protein from solution onto a solid plane is determined by the
stability of its structure. One unique characteristic of collagen is its structure
stability, and behaves as colloidal particles and only adsorbs onto ionic planes.
Jiao et al. (2006) studied the joint influence of Mg
2+ and collagen. It was confirmed
that Mg
2+ could stabilize amorphous calcium carbonate and control calcite
morphologies. They also found that Mg
2+ could induce spherical aragonite and
vaterite (small amount), and such action was amplified by collagen. But collagen
alone had no significant influence on calcium carbonate crystals, and almost all calcite
crystals were formed, which showed that collagen has a promotional effect on
magnesium ions in controlling the polymorph of CaCO 3 crystals (Fig. 6.18). They
also provided an explanation; magnesium is likely to react with collagen to change the
stereochemical structure of collagen molecules, and thus induced aragonite or vaterite.
As a summary of the above discussion, we think that polymorphs of the formed
crystals essentially lie on their nucleation energies in the system. There are three
ways to change nucleation priority: influence on DG surface like glycine, influence on
DG bulk like Mg ions, and influence on the relationship between DG surface and DG bulk
(influence on the nucleation type) like choosing low solution height.
176
Q. Feng
2+ combination could defer ACC transformation for the most
part, and such effect improved with the increase of Mg
2+ amount.
In biomineralization processes, the formation of inorganic crystals is controlled
by organic macromolecules such as proteins ((Mann 1996); (Addadi & Weiner
1985)). Collagen is the most important water-insoluble fibrin which represents the
framework of extracellular matrix. The basic structure of collagen is tropocollagen,
and its primary structure has a repetitive sequence of (Gly-x-y) n , of which x usually
represent Pro, and y of Hy-Pro of Hy-Lys. Shen et al. (2002) studied collagenmediated calcium carbonate crystal in vitro in order to reveal the principle of
protein-mediated mineralization process. The results of XRD and SEM of calcium
carbonate crystal deposition showed that only calcite was formed, and the calcite
growth is more and more inhibited as collagen is increased in concentration
(Fig. 6.17). It means that collagen does not change the polymorph of calcium
carbonates. With the increasing concentration of collagen, the morphology of calcite
changed from perfect rhombohedral to well-faceted rhombohedral crystals with
little disfigurement, and then to overgrown calcite crystals with new planes. The
thickness of new layers became thinner with the increasing of collagen, some of
calcite crystal planes would develop into a flowerlike form, and they become
spherulites as the concentration further increases (>10 g/l). They provided an
explanation, why collagen would absorb on the edges of {1 0 4} planes of calcite,
which are parallel to the c-axis, and inhibited its growth, thus new planes appeared.
The new planes started to appear at the edges of rhombohedral calcite crystals when
collagen was present in the solution, since crystal growth starts at edges and corners,
which provided good attachment sites; it led to the decrease of growth rate and new
plane growth on such positions. New planes formed have better attraction for
collagen, which would eventually alternate the morphologies. Collagen additives
not only influenced morphology of the crystals, but also the quantity. Number of
crystals increased, while size diminished with the increase of the protein concentration. The adsorption of protein from solution onto a solid plane is determined by the
stability of its structure. One unique characteristic of collagen is its structure
stability, and behaves as colloidal particles and only adsorbs onto ionic planes.
Jiao et al. (2006) studied the joint influence of Mg
2+ and collagen. It was confirmed
that Mg
2+ could stabilize amorphous calcium carbonate and control calcite
morphologies. They also found that Mg
2+ could induce spherical aragonite and
vaterite (small amount), and such action was amplified by collagen. But collagen
alone had no significant influence on calcium carbonate crystals, and almost all calcite
crystals were formed, which showed that collagen has a promotional effect on
magnesium ions in controlling the polymorph of CaCO 3 crystals (Fig. 6.18). They
also provided an explanation; magnesium is likely to react with collagen to change the
stereochemical structure of collagen molecules, and thus induced aragonite or vaterite.
As a summary of the above discussion, we think that polymorphs of the formed
crystals essentially lie on their nucleation energies in the system. There are three
ways to change nucleation priority: influence on DG surface like glycine, influence on
DG bulk like Mg ions, and influence on the relationship between DG surface and DG bulk
(influence on the nucleation type) like choosing low solution height.
176
Q. Feng