Biomedical Engineering Reference
In-Depth Information
layer on uniform Fe
3
O
4
particles. Second, through a surfactant templating
approach with CTAB as the template, mesoporous silica shells were depos-
ited on the nonporous silica/Fe
3
O
4
nanoparticles. Third, the CTAB templates
were removed by extraction to form perpendicularly aligned mesoporous
silica shells with thickness of around 70 nm. Gai et al. (2011) designed novel
fibrous-structured magnetic mesoporous silica particles with a core-shell
structure (denoted as Fe
3
O
4
/FMSMs). The Fe
3
O
4
/FMSMs exhibit a sustained
drug release profile, sufficient magnetic responsibility, and redispersibility
to the external magnetic field. Also, the Fe
3
O
4
/FMSMs nanoparticles could
be used as a therapeutically effective intracellular drug delivery system for
doxorubicin (DOX) delivery.
For the aforementioned magnetic mesoporous silica nanoparticles with
a core-shell structure, the magnetic cores are compactly stuck to the silica
shells, and therefore their magnetic properties may be compromised to some
extent. Magnetic mesoporous silica nanoparticles with rattle-type or yolk/
shell structure can prove to be a solution to this problem (Zhao et al. 2008; Lin
et al. 2009; Zhu et al. 2009; Chen, Chen, Zeng, et al. 2010; Liu et al. 2010; Tan et
al. 2010; Zhu, Fang, and Kaskel 2010; Zhu, Ikoma, et al. 2010; Chen, Chen, Ma,
et al. 2011; Wu et al. 2011; Zhang et al. 2011; Zhu, Jian, and Wang 2011; Zhu,
Meng, Gao, et al. 2011; Zhu, Meng, and Hanagata 2011), as such nanoparticles
possess unique structures with interstitial spaces between mesoporous silica
shells and magnetic cores, that is, movable magnetic nanoparticles encapsu-
lated in hollow mesoporous silica nanoparticles. Also, rattle-type magnetic
mesoporous silica nanoparticles are designed and applied as controlled drug
delivery carriers, because the large cavity volume between yolk and shell
can provide more space for loading drug molecules. Therefore, rattle-type
magnetic mesoporous silica nanoparticles can be used as multifunctional
platforms for biomedical applications, such as diagnostic agent and tar-
geted drug delivery. Shi's group has prepared a series of rattle-type Fe
3
O
4
@
mSiO
2
mesoporous ellipsoids/spheres with a single or double mesoporous
silica shells by using the so-called etching approach (Zhao et al. 2008; Chen,
Chen, Guo, et al. 2010; Chen, Chen, Zeng, et al. 2010; Chen, Chen, Ma, et
al. 2011; Wu et al. 2011). For example, Wu et al. (2011) first prepared Fe
2
O
3
/
SiO
2
/mSiO
2
core-shell structures, and rattle-type Fe
3
O
4
@mSiO
2
mesoporous
spheres were obtained by hydrothermally treating the Fe
2
O
3
/SiO
2
/mSiO
2
core-shell structures and following the reduction in an H
2
/N
2
atmosphere.
They proved that the saturation magnetization value of rattle-type Fe
3
O
4
@
mSiO
2
mesoporous spheres (35.7 emu/g) is evidently higher than that of the
corresponding core-shell structure with an intact middle silica layer (28.8
emu/g) due to the removal of the in-between silica layer (Wu et al. 2011). In
addition, surface area and pore volume of the rattle-type Fe
3
O
4
@mSiO
2
mes-
oporous spheres are calculated to be 435 m
2
/g and 0.58 cm
3
/g, respectively,
which are significantly higher than the sample with an intact middle silica
layer (274 m
2
/g and 0.38 cm
3
/g). Furthermore, these rattle-type Fe
3
O
4
@mSiO
2
mesoporous spheres possess high efficiency docetaxel (DOC) loading ability
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