Preparation and Mechanism of Novel Bioceramics with Controllable Morphology and Crystal Growth - Advanced Bioactive Inorganic Materials for Bone Regeneration and Drug Delivery - page 165

(a)

(b)

FIGURE 6.8
SEM images of the (a) electrospun BGF and (b) the obtained NHAHF after hydrothermal treat-
ment at 150°C for 2 h.

glass nanofiber nonwoven membrane in (NH 4 ) 2 HPO 4 aqueous solution at
150°C, the hierarchically structured nanocrystalline HAp assembled hollow
fibers were fabricated (Figure 6.8). Analogous to conventional hard template,
the bioactive glass nanofibers in our method cannot only play the role of a
structure-directing scaffold and a precursor for the shell but also automati-
cally dissolve during the shell-forming process. The progress is therefore
more efficient and the resulting hollow structure is continuous, uniform in a
larger scale, and controllable by changing the reaction time (Wu et al. 2011).

6.2.3 Morphology Control of the Bioceramics with
Oriented Structures Similar to Bone and Tooth

The natural human bone and tooth possess a highly organized array of
HAp crystallites on the nanoscale level and bundles of aligned crystallites
woven into intricate architectures on the microscale level (Habelitz et al. 2001;
LeGeros 2008). Such a unique hierarchical structure plays a critical role in
determining the excellent mechanical properties and biological properties
of them. It is also a great challenge to develop facile methods to fabricate
HAp materials with oriented hierarchical structure similar to bone and tooth
(Chen et al. 2006; Yang et al. 2011). It is clear that the processes of HAp crys-
tal nucleation and growth in the extracellular matrix are highly controlled
and directed by proteins. Therefore, the most popular strategy to synthesize
bonelike and enamel-like HAp is based on the protein-directing process
(Moradian-Oldak 2001). In enamel, processing of the matrix is concomitant
with the growth and maturation of enamel crystallites, and perhaps the step-
wise processing of amelogenin is one of the key factors to control some pro-
cesses of crystal growth. Amelogenin sequences at both carboxy- and amino
terminal regions across species are highly homologous suggesting that these
regions play specific functional roles during matrix mediated enamel biomin-
eralization (Toyasawa et al. 1998; Moradian-Oldak 2001). Wen et al. (2000)