Biomimetic Preparation and Morphology Control of Mesoporous Silica - Biomimetics: Advancing Nanobiomaterials and Tissue Engineering - page 307

delivery nanodevices. In this work, an MSN-based, controlled-release
delivery system has been synthesized and characterized using surface-
derivatized cadmium sulfi de (CdS) nanocrystals as chemically removable
caps to encapsulate several pharmaceutical drug molecules and neu-
rotransmitters inside the organically functionalized MSN mesoporous
framework.
Zink et al. combined mesostructured functional silica with novel
supermolecular techniques and have proposed nanomachines based on
the MSN by surface modifying, which is hopefully the most important
improvement for the future of the nanobiomedical fi eld.[41]. They have
described a series of recent mechanized silica nanoparticles, which, under
abiotic conditions, are capable of delivering cargo molecules employing a
series of nanovalves. The key question for these systems has now become
whether they can be adapted for biological use through controlled nano-
valve opening in cells. Figure 13.4 shows that they report a novel MSNP
delivery system capable of drug delivery based on the function of β -cyclo-

dextrin ( -CD) nanovalves that are responsive to the endosomal acidifi ca-

tion conditions in human differentiated myeloid (THP-1) and squamous
carcinoma (KB-31) cell lines. Furthermore, they demonstrate how to opti-
mize the surface functionalization of the MSNP so as to provide a platform
for the effective and rapid doxorubicin release to the nuclei of KB-31 cells.

β

13.4 Biomimic Preparation and Morphology Control

of Mesoporous Silica

13.4.1 General Synthesis

Of the fi ve elements such as solvent, surfactant, silica source, catalyst
and the acid-base properties used in the synthesis of mesoporous silica,
surfactant plays an important role. Much of the synthesis of mesopo-
rous silica is based on a surfactant template method that determines
templating routes. This is because the surfactant self-assemblies can act
as organic supermolecular template similar to that in biomineralization,
and the surface can be the reactant site on which the silica precursor can
be deposited. The surfactants are usually classifi ed by the head group
and charge as: cationic surfactants (the hydrophilic group carries a posi-
tive charge, e.g., tetraalkylammonium salts), anionic surfactants (the
hydrophilic group carries a negative charge, e.g., sulfates, sulfonates,
etc.), and neutral surfactant (nonionic alkyl-poly(ethylene oxide) (PEO)
oligomeric surfactants and poly-(alkylene oxide) block copolymers
(PO), respectively).
The main formation mechanism has been proposed as liquid-crystal
templating (LCT) [42-44], cooperative formation mechanism [24], and the
deposition of self-assembled silicate surfactant rod-like micelles [29, 30].