Functional Mesoporous Silica Nanoparticles with a Core-Shell Structure for Controllable Drug Delivery - Advanced Bioactive Inorganic Materials for Bone Regeneration and Drug Delivery - page 56

drug loading capacity. Therefore, the combination of iron oxide nanopar-
ticles and mesoporous silica to form magnetic mesoporous silica nanopar-
ticles would overcome the limitations and represent a significant advance in
the field of drug delivery (Liong et al. 2008; Zhang et al. 2008; Huang et al.
2012; Liu et al. 2012).
Recently, preparation of magnetic mesoporous silica nanoparticles has
received much interest. Different types of magnetic mesoporous silica
nanoparticles have been reported for controllable drug delivery, including
(1) embedding iron oxide nanocrystals into mesoporous silica matrices (Yiu
et al. 2010); (2) the core-shell structured nanoparticles with iron oxide core
and mesoporous silica shell (Wu et al. 2004; Zhao et al. 2005; Kim et al. 2006;
Deng et al. 2008; Kim et al. 2008; Zhao et al. 2008; Lin et al. 2009; Lin and
Haynes 2009; Zhu et al. 2009; Chen, Chen, Zeng, et al. 2010; Fu 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; Gai et al. 2011; Rosenholm, Sahlgren, 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); and (3) capping the pores of mes-
oporous silica with iron oxide nanocrystals for stimuli-responsive controlled
drug release (Giri et al. 2005; Gan et al. 2011). Among these magnetic meso-
porous silica nanoparticles, the core-shell structured nanoparticles with iron
oxide core and mesoporous silica shell are considered as the most important
and desirable structure for drug delivery combined with targeting or hyper-
thermia functions.
For the core-shell structure, the most straightforward synthetic strategy
is the so-called bottom-up approach, where the core and shell are prepared
in an inside-to-outside order. In 2004, Wu et al. for the first time reported
magnetic mesoporous silica particles with Fe 3 O 4 core and mesoporous sil-
ica shell, which are prepared via deposition of mesoporous silica film on
magnetic Fe 3 O 4 cores by using cetyltrimethylammonium chloride (CTACl)
micelles as structure-directing agents. Since then, different approaches have
been developed to prepare magnetic mesoporous silica nanoparticles with
a core-shell structure. Also, these magnetic mesoporous silica nanoparticles
have been used as carriers for application in drug delivery.
Self-assembly, phase transfer, and microemulsion techniques are effec-
tive routes to magnetic mesoporous silica nanoparticles with a core-shell
structure. For hydrophobic ligand-capped magnetic nanocrystals, they can
be successfully encapsulated into the mesoporous silica nanoparticles by
using CTAB surfactant as a structure agent and a coagent for transferring
the magnetic nanoparticles from oil to water, and the resulting nanoparticles
can be formed by encapsulating one to several magnetic nanocrystals into
one mesoporous silica nanoparticle. The size of these magnetic mesoporous
silica nanoparticles can be easily controlled. Kim et al. (2006) reported the
synthesis of monodisperse and size-controllable core-shell mesoporous sil-
ica nanoparticles by using single Fe 3 O 4 nanocrystals as cores (designated as
Fe 3 O 4 @mSiO 2 ) (see Figure 3.4). In this approach, hydrophobic ligand-capped