Preparation and Mechanism of Novel Bioceramics with Controllable Morphology and Crystal Growth - Advanced Bioactive Inorganic Materials for Bone Regeneration and Drug Delivery - page 166

found that after the addition of 1%~2% amelogenins to 10% gelatin gel the
OCP crystals became remarkably longer. The average aspect ratio (length/
width) of OCP increased remarkably with the increase of the concentration of
amelogenins, which suggested that the elongation effect was dose dependent
by amelogenin. Iijima et al. (2001) also found that the ratios of the length-
to-width and the thickness-to-width of the OCP crystals were increased in
the presence of amelogenins isolated from developing bovine enamel, as well
as recombinant amelogenins rM179 and rM166. These studies indicate that
amelogenin interacts more strongly with the (0 1 0) face, which inhibit the
growth of the crystals in the b-axial direction (the width). Analysis of the
particle size distribution of apatite crystal aggregates grown in the presence
of different amelogenins indicated that the full-length amelogenin caused
aggregation of apatite crystals more effectively than the C-terminally cleaved
amelogenin and other commercially available macromolecules (Moradian-
Oldak et al. 1998). The enamel-liked HAp aggregations were also reported
by using bovine amelogenin. The results also reveal that, as a well-known
effective modifier during in vivo tooth enamel formation, the amelogenin can
dramatically accelerate the kinetics of nanoassembly (Wang et al. 2007).
Tao et al. (2007) suggested a new model of ''bricks and mortar'' concern-
ing the biological aggregation of apatite nanoparticles. An inorganic phase,
amorphous calcium phosphate (ACP) acts as “mortar” to cement the crys-
tallized “bricks” of nano-HAp. Meanwhile, biological molecules control the
nanoconstruction. By using HAp nanospheres as the building blocks, highly
ordered enamel-like and bonelike apatite were hierarchically constructed in
the presence of glycine (Gly) and glutamate (Glu), respectively. It is interest-
ing that during the evolution of biological apatite, the amorphous mortar
can be eventually turned into the brick phase by phase transformation to
ensure the integrity of biominerals. Cai et al. (2009) simulated the assembly
of nanosized HAp crystals using the silk sericin (SS) as template. The SS con-
centration and mineralization time played important roles on crystal size,
morphology, and formation process (such as nucleation, growth, aggrega-
tion, especially assembly dynamics, etc.) of the products. When the concen-
tration of SS was kept at 1% (w/v) in the reaction system, the HAp crystals of
300 to 500 nm in length and 50 to 80 nm in diameter were assembled along
the c-axis and smaller crystals of about 20 nm were obtained. The size and
the assembled microstructures are similar to the natural enamel crystals.
The original self-assembled spherical-shape and subsequent conformational
transition of SS may be two major reasons to modulate the enamel prismlike
structure formation.
The enamel-like HAp crystals were synthesized by modifying the syn-
thetic HAp nanorods with a surfactant of AOT, which allowed the nanorods
to self-assemble into an enamel prismlike structure at the water-air interface
(Tornblom and Henriksson 1997). Ye et al. (2008) achieved highly oriented orga-
nization of HAp nanorods through a simple reflux method using mixtures of
triblock copolymer pluronic P123 and tween-60 as the mediated reagents.