Biomedical Engineering Reference
In-Depth Information
Generally, MBG with high contents of SiO 2 has a more ordered mesopore
structure, and higher specific surface area and pore volume than those of
low-SiO 2 MBG. The incorporation of Ca or P into a mesoporous SiO 2 sys-
tem significantly decreased its surface area and pore volume. Similarly, the
incorporation of divalent ions (Mg, Zn, Cu, or Sr), trivalent ions (Ce, Ga, or
B), and tetravalent ions (Zr) into a SiO 2 -CaO-P 2 O 5 MBG system also signifi-
cantly decreased its mesoporous properties (surface area and pore volume)
(see Table 1.1). It is interesting that the composition of MBG seems to have no
significant effect on the mesopore size, which is usually in the range of 3 to
5 nm. The results indicated that the incorporation of additional ions into an
MBG system may disrupt the ordered orientation of SiO 4 4- during the self-
assembly reaction, which may result in potential structural defects in the
atomic array and further change the shape and structures of mesopores (Wu,
Fan, et al. 2011). However, the MBG with varied components still possesses
high surface area (in the range of 150 to 500 m 2 /g) and pore volume (in the
range of 0.2 to 0.6 cm 3 /g; see Table 1.1) (Wu and Chang 2012).
1.2.2 Different Forms of MBG: Particles, Fibers,
Scaffolds, and Composites
MBG has been prepared as particles, fibers, spheres, 3D scaffolds, and com-
posites with a well-ordered mesoporous channel structure and excellent
bioactivity for drug delivery and bone regeneration application (Wu and
Chang 2012). MBG particles were first synthesized in 2004 by Yan and col-
leagues. The size of the obtained MBG particles was around several tens
of micrometers. The particles contained highly ordered mesoporous chan-
nels (5 nm) with high surface area and pore volume. After that, Lei, Chen,
Wang, Zhao, Du, et al. (2009) synthesized MBG powders with high specific
surface area by using acetic acid as a structure-assisted agent and hydrolysis
catalyst. MBG powders with different compositions (58S and 77S) were pre-
pared using P123 and hydrothermal treatment, both of which were shown
to have excellent in vitro bioactivity (Xia and Chang 2006, 2008). By using the
same method, Li, Wang, He, et al. (2008) prepared Mg-, Zn-, or Cu-containing
multicomponent MBG particles. Wu, Wei, et al. (2010) synthesized CaO-SiO 2
mesoporous MBG particles for hemostatic application. Recently, our group
developed a simple method to prepare MBG particles without hydrother-
mal treatment, which is suitable for large-mass production of MBG particles
(Feng and Chang 2011). Nanosized mesoporous MBG particles with a size
of around 100 nm were prepared and could be used as bioactive fillers to
infiltrate into dentinal tubules, carry/release antibiotics, and induce in vitro
mineralization (see Figure 1.1).
Hong, Chen, Jing, Fan, Guo, et al. (2010) prepared ultrathin MBG fibers
by electron spin techniques. In their study, ultrathin MBG fibers, with hier-
archical nanoporosities and high matrix homogeneities, were synthesized
using electrospinning techniques and P123-PEO cotemplates. At the same
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