Biomedical Engineering Reference
In-Depth Information
also because it is a great source of inspiration for the design of
advanced materials.
29
-
34
Previous investigations on the mineralization of HA crystals on
collagen fibers have suggested that the binding of calcium ions on
the negatively charged carboxylate groups of collagen is one of the
key factors for the first-step nucleation of HA crystals.
35
Other par-
tially negatively charged functional groups on collagen have previ-
ouslybeenconsideredtobepossiblenucleationsitesforHAcrystals.
It has been demonstrated, however, that carboxyl groups (-COOH)
are the major nucleation sites for collagen fibrils. In a neutral solu-
tion,thecarboxylgroupsareionizedtoCOO-,whichfavorschelation
of calcium ions. The carboxyl groups on the outside of the collagen
threefold spiral are also onekindof site forcollagen mineralization.
Zhang
et al
. have reported some investigations on the mineral-
ization of calcium phosphate crystals on collagen fibers by using
Fouriertransforminfraredspectroscopy(FTIR).
36
Forthefirsttime,
theysuccessfullyshowedthatintheinitialstageofcollagenmineral-
ization, collagen prefers to chelate calcium ions in solution and that
these chelated ions subsequently form nucleation sites for calcium
phosphatecrystals.Moreover,inadditiontotheirimportanceforthe
interfacial interaction between calcium ions and carboxyl groups,
the carbonyl groups on the surface of collagen molecules also act as
nucleation sites of calciumphosphate crystals.
In the recent research, it is reported that the conformation of
collagen changes rapidly during the amorphous/crystalline conver-
sion and crystal ripening. The results show the characteristics of
cooperative interaction between calcium phosphate and collagen
molecules, that is, collagen molecules control the nucleation of cal-
cium phosphate through providing nucleation sites, while collagen
molecules adopt different conformations to adapt the formation of
biominerals.
37
ArecentreviewbyPalmer
et al
.
38
alsocomprehensivelypresents
protein-based mineralization, nonprotein biopolymers mineral-
ization, synthetic polymers mineralization, and organoapatites
mineralization. In addition, they still described several supramole-
cular systems that have been developed in their own laborato-
ries, both as biomimetic mineralization models and as matrices for
bone regeneration. Liao
et al
.
39
have investigated the fabrication of
Search WWH ::
Custom Search