Biomedical Engineering Reference
In-Depth Information
and the HAP nucleation rate increases when structural matching between HAP and
amelogenin takes place. It has been proposed that aligned crystals tend to be formed
more often at a lower degree of supersaturation [ 51 , 52 ].
A future objective is to elucidate the effect of amelogenin on the aggregation of
HAP crystals aligned along the c -axis. Yang et al. proposed a model regarding the
interaction between amelogenin and nanoclusters of calcium phosphate [ 53 ]. This
model will be described in detail in Chap. 5.
As described above, Tarasevich et al. accelerated OCP deposition using mouse
amelogenin, while Wang et al. formed HAP using porcine amelogenin under
supersaturated conditions with respect to both HAP and OCP. In both cases,
amelogenin-induced heterogeneous nucleation accelerated crystallization. Does
mouse amelogenin structurally match OCP, whereas porcine amelogenin struc-
turally matches HAP? Why did porcine amelogenin fail to form HAP deposits? And
why did mouse amelogenin fail to form OCP deposits? To understand the template
effect of the proteins, it is necessary to analyze the effect of various protein templates
under uniform experimental conditions.
4.5
Controlling Crystal Growth
As described in Chap. 3, by analyzing step velocities on the growing crystal face
in the presence or absence of different proteins, the effect of these proteins on
crystal growth can be quantitatively evaluated. However, such an attempt has not
been achieved with HAP. In this section, we describe the effect of amino acids,
peptides, and proteins on the growth of calcite, one of the crystal phases of calcium
carbonate.
In general, when an impurity adsorbs to a crystal surface, the incorporation of
the crystal unit at the kinked site is inhibited, and the growth of the crystal face is
slowed. It was found, however, that acidic proteins extracted from pearl layers of
abalone, AP
, accelerated crystal growth. Although these proteins were
originally extracted from aragonite layers, their effects on the crystal growth were
investigated using calcite (104) surface [ 54 ].
Elhadj et al. focused on aspartic acid residues in acidic proteins, and quantita-
tively analyzed the effects of aspartic acid polypeptides (monomers to hexamers
(Asp1, Asp2, Asp3, Asp4, Asp5, Asp6)) on crystal growth of the calcite surface by
using AFM [ 55 ]. The calcite (104) surface consisted of an acute step and an obtuse
step, and the step velocities were increased in the presence of peptides. Peptides
containing a large number of aspartic acid residues resulted in increased acceleration
of crystal growth, and the effect was dose dependent. All peptides accelerated
crystal growth at a concentration of less than 1
'
and AP
M, and inhibited growth at
high concentrations. Interestingly, each peptide exhibited step specificity for the
acceleration. The growth of the acute step was affected by Asp1 and Asp2, and that
of the obtuse step was affected by Asp3 to Asp6. The interaction between calcium
atoms and peptides on the calcite surface indicates that the interaction between Asp3
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