Biomedical Engineering Reference
In-Depth Information
Fig. 5.3
Model of crystal formation in solution supersaturated with OCP: (a) without amelogenin,
random aggregates of OCP form. (b) With amelogenin, organized microstructures form: (1)
assembly of CaP clusters (red balls) and amelogenin oligomers (small nanospheres, gray ball);
(2) formation of amelogenin-CaP nanocrystallites as building units; (3) organized assembly of
building units into HAP nanocrystallites. (Reproduced with permission from ref. [
95
]) (Copyright
2007, American Chemical Society)
(CaP clusters) bind with amelogenin nanospheres and form amelogenin (amel)-
CaP clusters as basic building units. These clusters form amel-CaP nanocrystallites,
which subsequently assemble and form HAP nanocrystallites. The specific binding
is ascribed to the charged COOH-terminal region. An important point is that amel-
CaP nanocrystallites find the low-energy configurations needed to bind with the
adjacent crystallite. An NMR study revealed a direct amelogenin-HAP interaction
through the C-terminal region that oriented the C-terminal region on the HAP crystal
[
97
]. Without amelogenin, spherical aggregates of OCP nanocrystallite formed.
Ya n g
et al
. used a solution with H-Ap stoichiometry and undersaturated with
respect to OCP to analyze the nucleation process:
15.1, pH 7.4, 37
ı
C, ionic
HAP
D
strength
g/mL [
96
]. The reactions in solution with
lower supersaturation revealed the initial nucleation process. The newly observed
crystal formation process comprises five steps: (1) CaP clusters pre-nucleate with
adiameteroflessthan1nm.(2)Thepre-nucleated clusters are captured by
amelogenin, causing them to form amel-nano-CaP clusters, 2-10 nm in size, which
in turn form nanoparticles, 30-50 nm in size. The amel-CaP nanocluster compos-
ites transform into amel-ACP nanospherical building blocks. (3) The amel-ACP
nanospherules gradually assemble into nanochains. (4) The nanochains co-assemble
into nanorods or nanoribbons. (5) Ostwald ripening leads to elongated HAP.
Without amelogenin, random-sized CaP clusters formed and assembled into
globular ACP with an irregular size distribution. This globular ACP aggregated
D
0.15 M, with rP172 of 25
