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Mesoporous Silica in Biomedical
Applications
Luigi PASQUA
Department of Environmental and
Chemical Engineering
University of Calabria
Rende, ITALY
During the last 20 years an evolution towards
materials with larger pores than zeolites has been
obtained.
Ordered silica-based mesoporous materials named
M41s were introduced at the beginning of the 1990s.
Most of the synthesis approaches to form inorganic
mesoporous materials are generally based on the use
of organic template molecules.
They organize themselves in sopramolecular formation
around which the silica condensation occurs.
The knowledge of several synthesis methods and of the
parameters that affect the properties of the final material
that constitutes the
“field of existence of the mesoporous materials ”
give the material chemist the possibility to engineerize in
detail the system that he needs.
Synthesis of mesoporous materials
Choice a surfactant
type and the specific
synthesis mechanism
A mesoporous materials is produced
starting from the interaction of the
silica source with the template molecules
The first ordered mesoporous materials
(IUPAC: 2 nm <dp < 50 nm) that were
reported are known as the M41S-type of
silica mesophases. They were first reported
in 1992 by Mobil.
The Mobil researchers introduced selfassembling surfactants as structure directing
agents to direct the formation of the SiO2
mesostructured materials.
The key parameters for the M41S synthesis are
•the
•the
•the
•the
•the
hydrogel composition,
type and length of the surfactant,
alkalinity,
temperature and
synthesis time.
All M41S materials have well-defined uniform
pores that are ordered in the long range.
Among the applications:
catalysis , sorption,
separations, sensing, optics , drug delivery, drug
targeting
and
several
other
biomedical
applications can be cited.
Synthesis Mechanism of Mesoporous
Materials (S+ I-)
Silica oligomers
surfactant
micelles
Cylindric
Aggregates
Mesophase
MCM-41
Calcination
Micelles as templates for the addressing
of silica condensation.
MSU materials are prepared with nonionic polyethylene glycol
polymers in neutral environment.
Properties of Mesoporous Materials
Silica framework
High loading capacity (pore volume 0.5 – 1
cm3/g)
Homogeneous and tunable pore size
Versatile funtionalization
Tunable surface properties
(hydrophobic/hydrophilic)
Basic/acid groups
Hybridization of mesoporous silica
Hybrid inorganic-organic materials are produced
when chemically active groups are linked to the
inorganic framework of mesoporous materials
BY
1) Post Synthetic Grafting
Or
2) Simultaneous condensation of siloxane and
organo-siloxane precursors
Chem. Commun., (1996) p.1367;
Chem. Mater., 11 (1999) p. 3285;
Microp. and Mesop. Mater.,27 (1999) p. 329.
Post synthetic grafting
Co-Condensation
Pore system are suitably modified by chemicals
Modifying agents have to be reactive toward silica
walls
Modifying agents can carry, other than the binding
group, every kind of organic group on the opposite
side of the molecule
Appropriate active sites in terms of size polarity,
presence of chelating agents or metals can be
created.
Surface properties of calcined and
surfactant-extracted mesoporous
materials
Thermal treatment during calcination
induces dehydroxylation making
the surface strongly hydrophobic
3
Adsorbed volume (cm /g STP)
560
480
Des Aextr
Ads Aextr
Des Aextr Bz
Ads Aextr Bz
400
320
240
160
80
0.0
0.2
0.4
0.6
Relative pressure P/P0
0.8
1.0
Sample Bz/(SiO2 +
OH
Bz + ads.
conc.
H2O)
mol/100
(mass
g
ratio)
Dry
SiO2
Bz/(SiO2 +
Bz)
(mass
ratio)**
Bz/SiO2 + % of
Bz
OH
(mol/100g) reacte
d with
Bz
Acalc Bz 4.30·10-4 *
0.23
4.12·10-2
0.042
18
AextrBz 6.95·10-2 *
0.56
2.30·10-1
0.23
41
Table. Quantitative data on benzoyl and hydroxyl modification
*Data obtained from UV quantitative measurements of hydrolysis solution
**Data obtained from TG analyses
Drug targeting devices with mesoporous
materials
Design of a multifunctional device able to target a
drug:
The device is provided, on the external surface, with
a fluorescent marker and with a biological function
whose receptors are overexpressed from the most
type of human cancer cells;
The drug is loaded in the pores, the release
mechanism can be based on diffusion if adsorbed or
on the pH differences between extracellular
environment and endosomes if bonded.
Bifunctional hybrid mesoporous silica
potentially useful for drug targeting
has been synthesized starting from
neutral
surfactant-templated
mesoporous silica and covalently
coupling folic acid preferentially on
the external surface of the particles
Folic acid is the tested receptor-specific ligand
Folic acid, shows a great promise
as a tumour-homing agent in the
preparation of devices for drug
targeting to cancer cells.
This essential vitamin has a high affinity for
FR (Folate Receptors), which can actively
internalize bound folates and folate
conjugated
compounds
via
receptormediated endocytosis.
Furthermore, FR are over-expressed by
several kinds of cancer cells.
Thus folate conjugation to anti-cancer drugs
will improve drug selectivity and decrease
negative side effects.
Preparation of bifunctional mesoporous
silica potentially useful for drug targeting
L. PASQUA, F. TESTA, R. AIELLO, S.
CUNDARI and J. B.NAGY, Microporous and
Mesoporous Materials 103 (2007), 166-173.
Luigi Pasqua, Flaviano Testa, Rosario
Aiello, Umberto Maione,
PCT/IT2006/000167
Functionalization of mesoporous silica
with APTES
OCH2CH3
CH3CH2O
Si
CH3CH2O
CH2CH2CH2NH2
N
N
C
N
b
a
H
N
C
N
O H
f
C
N
O H
R
O
c
R-COOH
R
O
Si O
O
+ H2N
d
O
Si O
O
HN
O
e
The use of dicyclohexylcarbodiimides for
folic acid coupling (DCC or DIPC)is an
heritage of solid phase peptide synthesis
Folic acid is retained on the
surface of mesoporous silica also
when the same coupling reaction is
carried out without DCC or DIPC
This is due to ammonium salt
formation between amino group and
carboxilic group of folic acid.
The single reflection of XRD pattern of APMS1 and
surfactant extracted FAPMS1 are shown. The uniform
mesoporous structure of APMS1 is quite maintained after
coupling reaction and extraction procedure although a
partial broadening of silica as a consequence of the
different chemical treatments can be noted
Nitrogen adsorption–desorption isotherms of FAPMS1
before (bottom curve) and after surfactant extraction
(top curve). As expected, the pore volume increases
considerably after surfactant removal.
The chemical characterization of the folatederivatized material cannot be unambiguously carried
out because of the complexity of the hybrid material.
FT-IR spectrum of FAPMS2 sample ( 793 cm-1 N–H
out of plane wagging; 1417 cm-1 C–N amides stretching;
1531, 1608 cm-1 N–H bending; 1670–1700 cm-1 CO
amides stretching; 3106 cm-1 C–H aromatic stretching)
gives strong evidence of the association of folic acid
on the functional silica matrix.
To overcome this problems a series of parallel
experiments has been carried out in order to
reveal the chemical structure of the folatederivatized material.
The coupling reaction was carried out on
unfunctionalized mesoporous silica and on the
aminopropyl mesoporous silica without the use of
DCC so disabling, in the latter case, the reaction
system to produce amide bond with alpha or
gamma carboxylic groups of folic acid.
Furthermore, in order to subtract the
contribution of the surfactant during
chemical characterization of the material, a
pure silica matrix (BDH silica) functionalized
with aminopropyl groups (BDH silica and
APTES in refluxing toluene for 7 h) has been
employed, as reference, in the coupling
reaction with folic acid, (with and without
DCC) .
BDH silica functionalized with aminopropyl groups has
been coupled with heptanoic acid, a simple molecule
able to condense with amide bond formation
Folic acid is associated to the silica matrix
(mesoporous materials and BDH silica) both during
the coupling reaction with and without DCC (blank
proof); in the latter case the interaction is of
electrostatic.
Folic acid is retained on the material obtained
from
coupling reaction with DCC upon acid
treatment (HCl 0.3 M in EtOH) while it is
removed, by the same treatment, from the
material obtained from blank proof.
The acid solution is not able to hydrolyse the
amide bond at room temperature while
protonation is able to labilize the electrostatic
interaction between folic acid and the 3aminopropylsilica.
3-aminopropylsilica (BDH) (curve I); 3-aminopropylsilica
(BDH) coupled with folic acid without DCC after acid
treatment (curve II) and with DCC after acid treatment
(curve III).
Drug release profiles of CP. As expected, the
release is faster from MS compared to APMS1 and
FAPMS1. This behaviour is probably due to both to
steric hindrance and chemical interaction between
CP and functionalised matrices.
Preparation Steps
Synthesis of PEG-templated mesoporous silica
1 SiO2-0.52 decane - 0.324 Triton X-100-126.2 H2O
MSN
3-aminopropyltriethoxysilane functionalization
MSN-AP
Functionalization with folic acid
MSN-FOL
Cisplatin loading
MSN-FOL-Cp
N2 adsorptiondesorption
isotherms and
BJH adsorption
pore size
distribution
(insets) of
MSNs: a MSNExtracted and b
MSN-Fol
MSN SBET of 778 m2g-1 and PV at P/P0=0.9 of 0.50 cm3g-1.
MSN-FOL SBET of 460 m2g-1, PV at P/P0=0.9 of 0.48 cm3g-1
TEM micrographs of MSN-FOL material exhibits a
porous texture in adherence with materials of the
MSU family .
SEM images show that this synthesis procedure
yields nanoscaled particles without a regular
morphology appearing as aggregates of up to 500
nm.
Dynamic light scattering (DLS) measurements of
all functionalized particles showed that, when
suspended in water, their average size
distribution ranges between 100 to 300 nm
Fluoresceina
Cisplatino
C. Morelli, P. Maris, D. Sisci, E. Perrotta, E. Brunelli, I.
Perrotta, M. L. Panno, A. Tagarelli, C. Versace, M. F. Casula,
F. Testa, S. Ando, J. B. Nagy ,L. Pasqua*
Nanoscale, 2011, 3, 3198
Interestingly, MSN never entered HeLa , nor other
cancerous (T47D, MCF-7 and SKBR3) and normal
(HEK293) cell lines, indicating that calcined, non
functionalized, particles are inert and do not interact
with the biological systems.
Successively, we questioned whether the cellular
uptake depends on the electrostatic interactions
between the protonated aminopropyl (AP) groups
bound to the particles surface and the negatively
charged cell membranes. The results showed that
AP groups do not significantly affect the
endocytotic process,
In all cell lines, particle uptake occurs as soon as
after 1 h of incubation and the majority of cells
appear free of particles within 96 h, clearly
underlining MSNs biocompatibility.
Colloidal-gold labelling for FR unambiguously
demonstrated that MSN-FOL enter HeLa cells
through FR mediated endocytosis.
As expected, a
strong growth arrest
was observed after
one day in MSNFOLCp treated HeLa
cells, if compared to
the less dramatic
growth retardation
caused by comparable
amounts of free Cp
1) Intravenous administration of highly fluorescent FITC-MS in
healthy mices.
2) Intraperitoneal administration of highly fluorescent FITC-MS in
healthy mices.
Luigi PASQUA
Antonella LEGGIO
Catia MORELLI
NanoSiliCal Devices is a recently founded spin-off
company in the University of Calabria devoted to the
production of mesoporous silica-based smart devices for
targeting and release of biologically active molecules.
PRODUCTS:
-Patent licensing
-MSN provided with a mechanism able to release a drug in
intracellular compartment and a targeting function;
-Mesoporous silica-based systems for controlled drug release;
-Fluorescent MSN as imaging diagnostics;
-MSN for gene therapy
Bibliography
Pasqua L, Testa F, Aiello R, Cundari S, Nagy JB. Micropor Mesopor Mat.
2007;103:166-73.
Pasqua L, C. Morelli, F. Testa, D. Sisci, E. Brunelli, R. Aiello, S. and, J.
B.Nagy (2007). Stud. Surf. Sci. Catal., vol. 170, ISSN: 0167-2991
Pasqua L, Cundari S., Ceresa C., Cavaletti G. (2009). Curr Med Chem
vol. 16, p. 3054-3063, ISSN: 0929-8673
C. Morelli, P. Maris, D. Sisci, E. Perrotta, E. Brunelli, I. Perrotta, M.L.
Panno, A. Tagarelli, C. Versace, M.F. Casula, F. Testa,S. Andò, J.B. Nagy
and L. Pasqua. Nanoscale. 2011;3:3198-207.
Ceresa C, Nicolini G, Rigolio R, Bossi M, Pasqua L, Cavaletti. G. Curr
Med Chem. 2013;20:2589-600.
AIELLO R, MAIONE U, PASQUA L, TESTA F (2006). PCT/IT2006/000167,
UNIVERSITA' DELLA CALABRIA