Mesoporous Bioactive Glasses for Drug Delivery and Bone Tissue Regeneration - Advanced Bioactive Inorganic Materials for Bone Regeneration and Drug Delivery - page 4

prepared mesoporous bioactive glasses (MBG) in 2004 by combining the sol-
gel method and supramolecular chemistry of surfactants. Their study has
opened a new direction for applying nanotechniques to regenerative medi-
cine by coupling drug delivery with bioactive materials. These materials are
based on a CaO-SiO 2 -P 2 O 5 composition and have a highly ordered mesopore
channel structure with a pore size ranging from 5 to 20 nm. Compared to
conventional nonmesoporous bioactive glass (NBG), the MBG possesses a
more optimal surface area, pore volume, ability to induce in vitro apatite min-
eralization in simulated body fluids, and excellent cytocompatibility (Yan et
al. 2006; Leonova et al. 2008; Garcia et al. 2009; Alcaide et al. 2010). The study
of MBG for drug delivery and bone tissue engineering has been becoming
a hot area of research during the past 5 years (Wu and Chang 2012). In this
chapter, we will highlight the recent advances of MBG materials for drug
and growth factor delivery and bone regeneration applications.
1.2 Preparation, Compositions, and Main Forms of MBG
1.2.1 Preparation Methods and Compositions of MBG
The preparation method of MBG is similar with that for mesoporous SiO 2 , in
which the supramolecular chemistry has been incorporated into the sol-gel
process. In this strategy, the incorporation of structure-directing agents (e.g.,
CTAB, P123, and F127) is essential for obtaining well-ordered structures.
Under appropriate synthesis conditions, these molecules self-organize into
micelles. Micelles link the hydrolyzed silica precursors through the hydro-
philic component and self-assemble to form an ordered mesophase (Arcos et
al. 2009; Arcos and Vallet-Regi 2010). Then the reaction mixture of bioactive
glasses and structure-directing agents underwent an evaporation-induced
self-assembly (EISA) process. A general definition of EISA is the spontane-
ous organization of materials through noncovalent interactions (hydrogen
bonding, van der Waals forces, electrostatic forces, etc.) with no external
intervention (Brinker et al. 1999). In the EISA process of MBG, the surfactants
assemble into micelles, spherical or cylindrical structures that maintain the
hydrophilic parts of the surfactants in contact with the composition of bio-
active glasses (Si, Ca, and P elements, etc.) while shielding the hydrophobic
parts within the micellar interior. Once the mixture is dried and the surfac-
tant removed, a well-ordered mesoporous structure will be obtained, exhib-
iting high surface area and porosity (Arcos and Vallet-Regi 2010; Wu and
Chang 2012).
As pure mesoporous SiO 2 lacks adequate bioactivity, MBG has been devel-
oped with multicomponents based on SiO 2 -CaO or SiO 2 -CaO-M x O y (M: P,
Mg, Zn, or/and Fe, etc.) to enhance their bioactivity and special functions.