FUNCTIONAL NANO- AND MICROPARTICLES FOR DRUG, NUTRITION, AGRO AND ENVIRONMENTAL APPLICATIONS

FUNCTIONAL NANO- AND MICROPARTICLES
FOR DRUG, NUTRITION, AGRO AND
ENVIRONMENTAL APPLICATIONS
O. Kammona, K. Kotti, E. Dini, O. Kotrotsiou, S. Alexandridou and C. Kiparissides*
Chemical Engineering Department and Chemical Process Engineering Research
Institute, Aristotle University of Thessaloniki, P.O. Box 472, 54124, Thessaloniki,
Greece
Abstract
The rapid evolution of nanotechnology is aiming to fulfill the goal of optimal drug delivery, for various
types of diseases, through the development of advantageous targeted drug carriers (e.g., nanoparticles,
liposomes, micelles) with properly modified surfaces in order to avoid interactions with other vehicles,
cells and proteins and thus with increased lifetimes, as well as through the attachment of model ligands
to drug vesicles for increased targeting efficiency and the synthesis of molecularly imprinted polymers
(MIPs). In addition, nanotechnology is expected to meet the societal requirements for high-quality
potable water and environmentally friendly industrial processes with minimal solid/liquid wastes
through the development of specially designed functional nanoparticles, and their subsequent
impregnation into inorganic substrates.
Keywords
Targeted drug delivery, functional nanoparticles, liposomes, molecular imprinting, channel proteins,
water purification, electrodeposition.
Introduction
The on-going discovery of novel phenomena and
processes at the nanometer scale is providing science with
a wide range of tools, materials, devices and systems with
unique
characteristics.
Nanostructured
materials,
nanodevices and novel nanofabrication processes have
created great excitement in biomedical and environmental,
research and technologies because of their numerous and
diverse applications. The capability of synthesizing and
processing nanoparticles with tailored structures and
enhanced properties provide tremendous opportunities for
designing novel materials of exceptional promise for
biomedical and environmental applications. In the field of
biomedicine, nanotechnology will help reach the elusive
goal of active drug targeting to specific cells within the
body by the development of miniature drug-carriers (e.g.,
nanoparticles, liposomes, micelles) with increased
lifetimes, Alexandridou and Kiparissides (2002), as well
as through the synthesis of molecularly imprinted
polymers (MIPs). In the field of environmental
technologies, nanotechnology is expected to contribute to
a safer environment through the application of functional,
tailor-made nanoparticles to water treatment processes and
* To whom all correspondence should be addressed
to various industrial processes (e.g., production of
electrogalvanized steel, miniature connectors, etc).
In the present study, some of the on-going and novel
research activities of the Laboratory of Polymer Reaction
Engineering in the field of biomedicine and environmental
technologies are presented.
Biomedical Applications
Liposomes - Composite PLGA Microparticles
Liposomes are microscopic and submicroscopic
vesicles with sizes ranging from 10nm to 20µm. They are
usually made up of phospholipids, although other
amphiphiles such as nonionic surfactants can also be
employed for their construction. When phospholipids are
hydrated, they spontaneously form spherical lipid bilayers
enclosing the aqueous medium and the solute. Liposomes
offer several advantages over other delivery systems
including biocompatibility, control of biological properties
via modification of physical properties (e.g., lipid
composition, vesicle size, lipid membrane fluidity etc.)
and several modes for drug delivery to cells (e.g.,
absorption, fuse, endocytosis, phagocytosis) (Figure 1).
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Liposomes can be classified according to the number of
the lipid bilayers as unilamellar vesicles (ULVs) and
multilamellar vesicles (MLVs).
fuse
endocytosis
absorption
of hydroquinone or of hydroquinone-loaded liposomes
was added to a PLGA solution in dichloromethane
resulting in the formation of a w/o emulsion, Hans and
Lowman, (2002). The latter was then added to an aqueous
PVA solution leading to the formation of a w/o/w
emulsion. Simple and composite (Figure 3b), spherical
PLGA microparticles were formed by solvent evaporation
from the w/o/w emulsion at increased temperature. The
release rate of hydroquinone from the composite PLGA
microparticles was compared to that from the simple ones
and was found to be significantly retarded.
phagocytosis
Figure 1. Drug delivery modes
Functionalized liposomes can be synthesized using
peptides and oligosaccharides (Figure 2) in order to
achieve both targeting and circulation longevity. Peptides
can be used in order to guide liposomes to desired
receptors whereas, PEO-grafted phospholipids are known
to dramatically increase liposome survival in the
circulation. A surface modified liposomal drug delivery
vehicle can be developed for selective targeting by
coupling an RGD peptide to the liposome through a PEO
spacer, Lestini et al., 2002.
Hydrated
oligosaccharide
interface
Drug
Covalently
coupled
peptides
8080-100 nm
Figure 2. Functionalized liposome
In the present study, MLVs were synthesized using
hydration, followed by sonication and extrusion. Various
types of phospholipids (e.g., Phospholipon 80, 80H, 90
and 90H) and cholesterol were employed for their
synthesis. Hydroquinone, a hydrophilic drug used for skin
whitening was employed as the active ingredient. The
morphology of the MLVs after the hydration step was
examined by means of optical microscopy (Figure 3a) and
their size distribution was measured using dynamic light
scattering. The size of the MLVs was found to depend on
the preparation method, the type of the phospholipid and
the pore size of the membrane used during the extrusion
process.
The hydroquinone-loaded MLVs were subsequently
encapsulated in PLGA microparticles employing a
complex
solvent
evaporation
process.
PLGA
microparticles containing hydroquinone were also
prepared using the same technique. An aqueous solution
2
(a)
(b)
Figure 3. Optical micrograph of (a) MLVs prepared
by hydration and (b) composite PLGA particles
Antibody-directed Enzyme Prodrug Therapy(ADEPT)
Antibody-directed enzyme prodrug therapy (ADEPT)
is a two-step, therapeutic strategy, which aims to improve
the selectivity of anticancer drugs. In ADEPT, an enzyme
is linked to an antibody (Ab) (Ab-enzyme conjugate) that
binds to an antigen preferentially expressed on the surface
of tumor cells. Subsequently, the enzyme activates and
converts a nontoxic prodrug injected at the tumor, into a
cytotoxic drug (Figure 4).
The enzymes used for ADEPT must be stable under
physiological conditions and able to catalyze a scission
reaction of the prodrug. In addition, their catalytic
properties should be different from those of any
circulating endogenous enzyme and ideally, they should
be able to activate a panel of anticancer prodrugs. The
main requirement of Ab-conjugates is that they must
localize on the tumor with high affinity and have
minimum binding to normal sites. In addition, the covalent
binding of the enzyme should not destroy the ability of the
Ab to bind to its associated antigen, nor should it alter the
enzyme activity and there should be a rapid clearance of
the Ab-enzyme conjugate from the body fluids. Finally,
the prodrugs designed for ADEPT must be chemically
stable with good pharmacological and pharmacokinetic
properties, less cytotoxic than their corresponding active
drugs and suitable substrates for the activating enzyme,
Niculescu-Duvaz and Springer (1997).
Advanced Materials and Nanotechnology
immobilized
enzyme
inactive
prodrug
immobilized
antibody
antigen
binding site
(a)
(b)
Figure 5. Reconstitution of channel proteins in (a) ABA
triblock copolymer membranes and (b) nanoreactors
active drug
target tumor cell
active drug inside the cell
Figure 4. Schematic representation of ADEPT
Channel Proteins
Spherically closed triblock copolymer membranes can be
prepared in dilute aqueous solutions using an amphiphilic
ABA triblock copolymer, consisting of a flexible,
hydrophobic poly (dimethylsiloxane) (PDMS) middle
block and two water-soluble poly(2-methyloxazoline)
(PMOXA) side blocks. The PMOXA-PDMS-PMOXA
triblock copolymer vesicles thus formed carry
methacrylate end groups, which can be polymerized
within these self-assembled structures under preservation
of the characteristic membrane structure. As a result of the
crosslinking polymerization, the individual triblock
copolymer molecules are covalently linked together,
which leads to a considerable mechanical stabilization of
the membranes. The PMOXA-PDMS-PMOXA triblock
copolymer membranes can be employed for the
reconstitution of transmembrane proteins (e.g., outer
membrane protein F (OmpF) and maltoporin) The latter
form trimeric channels which allow the diffusion of small
solutes like ions, nutrients or antibiotics across the
polymeric membrane (Figure 5a) (Meier et al., 2000).
Channel proteins can also be reconstituted in enzyme
containing polymer-stabilized liposomes or triblock
copolymer nanocapsules (e.g., nanoreactors) in order to
control the rate of the reaction in the interior (e.g.,
hydrolysis of β-lactam antibiotics like ampicillin by the
enzyme β-lactamase) by controlling the permeability of
the solute (e.g., ampicillin) (Figure 5b) (Winterhalter et
al., 2001).
Molecularly Imprinted Polymeric Nanoparticles
Molecular imprinting of synthetic polymers is a
process where functional and cross-linking monomers are
co-polymerized in the presence of the target analyte i.e.,
the imprint molecule, which acts as a molecular template.
The functional monomers initially form a complex
with the imprint molecule, and following polymerization,
their functional groups are held in position by the highly
cross-linked polymeric structure. Subsequent removal of
the imprint molecule reveals binding sites that are
complementary in size and shape to the analyte (Figure 6).
Three particular features have made molecularly imprinted
polymers (MIPs) the target of intense investigation: i) their
high affinity and selectivity, which are similar to those of
natural receptors, ii) their unique stability which is
superior to that demonstrated by natural biomolecules and
iii) the simplicity of their preparation. Molecularly
imprinted polymers can be prepared in a variety of
physical forms to suit the final application desired (Byrne
et al., 2002; Allender et al., 2000).
Complex
Formation
Functional
monomers
Template
molecule Polymerization
Extraction
Figure 6. Schematic representation of molecular
imprinting
In the present study, precipitation polymerization was
employed for the synthesis of MIP nanoparticles to be
used as synthetic receptors selective for theophylline (Ye
et al., 2000; Ciardelli et al., 2004) and simazine (Matsui et
al., 1995). Non-imprinted polymeric nanoparticles were
also prepared using the same technique. The surface
examination of the polymeric particles revealed that both
MIP and non-imprinted particles exhibit a rough, porous
surface (Figure 7) indicating that the presence of the
template does not influence significantly the polymer
morphology. UV spectroscopy was employed to measure
the affinity and selectivity of the MIP particles. A small
amount of nanoparticles (e.g., 0.1gr) were incubated
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2004, Workshop of CPERI
overnight at room temperature in print molecule/
acetonitrile solutions of known concentrations (e.g., 1.4
µmole of theophylline/ml of solvent and 0.8 µmole of
simazine/ml of solvent). The binding capacity of the MIP
particles was compared to that of the non-imprinted
polymeric nanoparticles. It was shown that the
nanoparticles, which were imprinted with theophylline
adsorb 14.57 µmole of theophylline per 1gr of polymer
whereas, those imprinted with simazine were found to
adsorb 2.2 µmole of simazine per 1gr of polymer. When
non-imprinted polymeric nanoparticles were used, 3.12
µmole of theophylline per 1gr of polymer were adsorbed,
whereas, in the case of simazine, minimal binding of the
target analyte was observed. Competitive analysis was
also performed employing caffeine, an analyte which is
chemically-related to theophylline, in order to examine the
selectivity of the theophylline imprinted polymeric
receptors. It was shown that the MIP nanoparticles adsorb
1.79 µmole of caffeine per 1gr of polymer thus, proving
the selectivity of the artificial receptors towards the
template molecule.
(a)
In the present study, poly (styrene/β-cyclodextrin)
P(St/β-CD) and highly crosslinked poly(styrene/metadiisopropylbenzene) P(St/mDIB) porous nanoparticles
were prepared employing emulsifier-free emulsion
polymerization and a single-step swelling and
polymerization process (Cheng et al., 1992; Ogino et al.,
1995) to be used as hosts for the recovery of organic
components from potable water. The effect of the
crosslinker concentration on the particle morphology was
examined experimentally. The surface morphology of the
polymeric particles was assessed by scanning electron
microscopy (SEM) (Figure 8) and their pore size
distribution was determined by nitrogen adsorption. A
GC-FID method was employed to measure the adsorption
efficiency of the particles in various pollutants. The
adsorption experiments were carried out in a batch mode
and the Freundlich constant (KF) was calculated in terms
of the initial and equilibrium pollutant concentrations,
volume of the aqueous solution and mass of the adsorbent
(Jung et al., 2001). Adsorption measurements with
activated carbon (AC) were also performed for
comparison purposes. It was shown that the particles
examined have a moderate affinity for styrene, a low
affinity for chloroform and dibromochloromethane and a
high affinity for trichloro-ethylene and tetrachloroethylene
higher than that of activated carbon (Table 1).
(b)
(a)
(b)
(c)
Figure 7. SEM photomicrographs of (a) non-imprinted
polymeric nanoparticles and nanoparticles imprinted with
(b) theophylline and (c) simazine
(c)
Environmental Applications
Water Purification
Activated carbon has been traditionally used for water
purification. However, despite its relatively broad range of
effectiveness in adsorbing organic substances from
aqueous solutions, activated carbon cannot be considered
as a water treatment panacea, Weber (1973). Thus, there is
an emerging need for the development of improved,
alternative purification systems (e.g., porous polymeric
nanoparticles, composite membranes etc.).
4
Figure 8. SEM photomicrographs of the (a,b) P(St/mDIB)
and (c) P(St/βCD) nanoparticles
The porous nanoparticles were subsequently deposited
onto ceramic carriers (e.g., SiC/TiO2, alumina), resulting
in the formation of hybrid membranes. It was shown that
the P(St/mDIB) and P(St/β-CD) particles were distributed
rather homogeneously in the ceramic filters and a high
percentage of coverage was achieved (Figure 9).
Advanced Materials and Nanotechnology
Table 1. Adsorption efficiency of the polymeric
nanoparticles in various pollutants
Sam ple
Kf
1/n
Styrene
EP-PSmD IB -009
38.6456
SW P-PSm D IB -001 58.3579
EP-PSβCD -001
27.7140
0.88694
0.57390
0.92570
Trichloroethylene
EP-PSmD IB -009
203.376
SW P-PSm D IB -001 156.460
EP-PSβCD -001
132.620
Activated Carbon
89.39
0.43484
0.78340
0.44104
0.61253
unfriendly pre-treatment process, presently used to ensure
good paint adhesion onto electrogalvanized steel. The
polymerization experiments were carried out in
laboratory-scale glass reactors and the most promising
recipes were successfully scaled-up in a fully automated
pilot-scale reactor. The polymer containing zinc coatings
were produced at K.U. Leuven by electrolytic
codeposition of the particles from an acid zinc plating bath
using a rotating disk electrode (RDE). The coatings thus
prepared (Figure 11), were subsequently painted and
subjected to a number of corrosion resistance and paint
adhesion tests, which gave rather promising results.
Tetrachloroethylene
EP-PSmD IB -009
201.604
EP-PSβCD -001
155.310
SW P-PSm D IB -001 62.216
Activated Carbon
111.276
0.4408
0.9283
0.8284
0.7913
Chloroform
EP-PSmD IB -009
EP-PSβCD -001
Activated Carbon
3.3083
0.1332
5.9786
1.2812
1.5630
0.9854
D ibrom ochlorom ethane
EP-PSmD IB -009
EP-PSβCD -001
Activated Carbon
10.0299
9.9977
4.6419
0.86406
0.76424
1.2024
(a)
(b)
(c)
(a)
Figure 10. SEM photomicrographs of the (a) PS, (b)
P(MMA/DMAEMA) and (c) PGMA nanoparticles
(b)
Figure 9. Alumina filter containing P(St/β-CD)
particles: (a) peripheral surface, (b) horizontal section.
Figure 11. Codeposition of P (St/2-HEMA)
nanoparticles from an acid zinc-plating bath using an
RDE
Electrogalvanized Steel with Improved Properties
Monodisperse polymeric nanoparticles with diameters
in the range of 60 - 1400 nm, with various surface charges
and functional groups were prepared by (emulsifier-free)
emulsion polymerization (Figure 10) and incorporated into
electrolytic zinc coatings aiming to improve the corrosion
resistance of painted and unpainted electrogalvanized steel
and to eliminate phosphating, an environmentally
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2004, Workshop of CPERI
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