Post on 26-Mar-2015
Nanoparticles
1
Nanoparticles are the most extensively
investigated drug delivery systems.
This includes:
Polymeric nanoparticles
&
Liposomes
2
Nanoparticles are solid colloidal particles ranging insize from 10 to 1,000 nm. They are made of a macromolecular material which can be of synthetic or natural origin.Depending on the process used for their preparation, twodifferent types of nanoparticles can be obtained,nanospheres and nanocapsules. Nanospheres have a matrix-type structure in which a drug is dispersed,whereas nanocapsules exhibit a membrane-wall structurewith a core containing the drug. Because these systems have very high surface areas, drugs may also be adsorbed on their surface.
Polymeric nanoparticles
3
Methods of manufacturing nanoparticles
The choice of the manufacturing method depends on the raw material intended to be used and on the solubility characteristics of the active compound to be associated to the particles. The raw material, biocompatibility, the degradation behavior, choice of the administration route, desired release profile of the drug, and the type of biomedical application determine its selection.Thus nanoparticle formulation requires an initial and very precise definition of the needs and objectives to be achieved.
MANUFACTURE OF NANOPARTICLES
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1- In situ polymerization of a monomer
Nanospheres Two different approaches have been
considered for the preparation of
nanospheres by in situ
polymerization, depending on
whether the monomer to be
Polymerized:
is emulsified in a nonsolvent phase
(emulsification polymerization),
or dissolved in a solvent that is a
nonsolvent for the resulting polymer
(dispersion polymerization)
5
Emulsification Polymerization.
Depending on the nature of the continuous phase
in the
emulsion, whether, the continuous phase is
aqueous (o/w emulsion), or organic (w/o emulsion).
In both cases the monomer is emulsified in the
nonsolvent phase in presence of surfactant
molecules, leading to the formation of monomer-
swollen micelles and stabilized monomer droplets. 6
The polymerization reaction takes place in the
presence of a chemical or physical initiator.
The energy provided by the initiator creates free
reactive monomers in the continuous phase which
then collide
with the surrounding unreactive monomers and
initiate
the polymerization chain reaction.
The reaction generally stops once full consumption
of monomer or initiator is achieved.
7
The mechanism by which the polymeric particles are
formed during emulsification polymerization is by
micellar polymerization, where the swollen-monomer
micelles act as the site of nucleation and
polymerization.
Swollen micelles exhibit sizes in the nanometer range
and thus have a much larger surface area in
comparison with that of the monomer droplets.
Once generated in the continuous phase, free
reactive monomers would more probably initiate the
reaction within the micelles. 8
allowing the polymerization to be followed within
the micelles.
So, in this case, monomer droplets would essentially
act as monomer reservoirs.
As the monomer molecules
are slightly soluble in the
surrounding phase, they
reach the micelles by
diffusion from the monomer
droplets through the
continuous phase, thus
9
The drug to be associated to the nanospheres may be
present during polymerization or can be subsequently
added to the preformed nanospheres, so that the
drug can be either incorporated into the matrix or
simply adsorbed at the surface of the nanospheres.
10
Micellar polymerization mechanism.11
Dispersion Polymerization
The monomer is no more emulsified but dissolved in
an aqueous medium which acts as a precipitant for
the polymer to be formed.
The nucleation is directly induced in the aqueous
monomer solution.
For Production of Polymethacrylic Nanospheres, water
soluble methyl methacrylate monomers are dissolved
in an aqueous medium and polymerized by y-irradiation or by chemical initiation (ammonium or
potassium peroxodisulfate) combined with heating to
temperatures
above 650C. 12
In the case of chemical initiation, the aqueous medium
must be previously flushed with nitrogen for 1 h in
order to remove its oxygen content, which could
inhibit the polymerization by interfering with the
initiated radicals. Oligomers (primary polymer) are
formed and above a certain molecular weight
precipitate in the form of primary particles. Finally,
nanospheres are obtained by the growth or the fusion
of primary particles in the aqueous phase
13
The removal of detergents is very important that
produce very slowly biodegradable and
biocompatible nanoparticles The technique can be
used for vaccination purposes.
where initiation by y-irradiation can be useful for
the production of nanospheres by polymerization in
the presence of antigenic material at room
temperature,
thus preventing its destruction.
Examples of antigenic materials used to produce
nanoparticulate were different influenza antigens. 14
Nanocapsules
Nanocapsules is a colloidal carrier with a capsular
structure consisting of a polymeric envelope
surrounding
an oily central cavity containing lipophilic drugs.
Interfacial Polymerization Mechanism
The monomer (isobutyl cyanoacrylate) and a
lipophilic drug (progesterone) are dissolved in an
ethanolic phase containing an oil (Myglyol®,
Lipiodol®) or a non-miscible organic solvent
(benzylic alcohol).
15
This mixture is slowly injected through a needle into
a magnetically stirred aqueous phase (pH 4—10)
containing an nonionic surfactant (poloxamer 188).
Upon mixing with the aqueous phase, ethanol
rapidly
diffuses out of the organic phase giving rise to
spontaneous emulsification of the oil/monomer/drug
mixture.
Immediately the monomer molecules polymerize at
the water-oil interface, leading to the formation of
solid wall-structured particles. 16
The mixture immediately becomes milky and
nanocapsules with a mean diameter of 200-300 nm
are formed.
The colloidal suspension can then be concentrated
by evaporation under reduced pressure and filtered.
17
For encapsulate hydrophilic compounds such as
doxorubicin and fluorescein, inverse emulsification
polymerization
Technique can be used.
In this procedure, the drug was dissolved in a small
volume of water and emulsified in an organic
external phase
( hexane) containing a surfactant.
An organic solution of cyanoacrylate monomers is
added to the w/o emulsion.
Nanocapsules are formed, resulting from an
interfacial polymerization process around the
nanodroplets.
18
1.Most of the carriers produced by polymerization
have inadequate biodegradability properties
preventing their use for regular therapeutic
administration.
Only for vaccination purposes is being suitable
when
achievement of a very prolonged immune
response is desired.
2. The possible inhibition of drug activity due to
interactions with activated monomers present in
polymerization processes.
Disadvantages of preparation by
in situ polymerization of a monomer
19
3. It is very difficult to calculate the molecular
weight of the resulting polymerized material due
to the multicomponent nature of the
polymerization media. However, the
determination of molecular weight is very
important as it influences the biodistribution and
release
of the polymeric carrier.
4. The presence of toxic residues due to the
unreacted monomer, initiator, and surfactant
molecules whose elimination requires time-
consuming and not always efficient procedures.
20
In order to avoid those limitations and produce
biodegradable, well-characterized, and nontoxic
nanoparticles., already polymerized materials have
been used.
These materials include natural macromolecules
(biopolymers) and synthetic polymers.
21
2- Dispersion of a Preformed Polymer2- Dispersion of a Preformed Polymer
Nanospheres Prepared From Natural MacromoleculesNanospheres Prepared From Natural Macromolecules
Due to their biodegradability and biocompatibility,
example of natural macromolecules used for the
manufacture of nanospheres are:
Proteins as albumin, gelatin,
(the most widely used)
Polysaccharides as alginate or agarose
22
Two manufacturing techniques are used to produce
nanospheres from natural macromolecules.
1. The first technique is based on the formation
of a w/o emulsion followed by heat denaturation
or
chemical cross-linking of the macromolecule.
2.The second technique is a phase separation
process in an aqueous medium followed by
chemical crosslinking. 23
Emulsification-Based Methods
An aqueous solution of albumin is emulsified at
room temperature in a vegetal oil (cottonseed oil)
and homogenized either by a homogenizer or an
ultrasonication.
Once a high degree of dispersion is achieved, the
emulsion is added drop wise to a large volume of
preheated oil (>120°C) under stirring.
This leads to the immediate vaporization of the
water contained in the droplets and to the
irreversible denaturation of the albumin which
coagulates in the form of solid nanospheres. 24
The suspension is then cooled
at room temperature or in an
ice bath.
For complete removal of the
oil, wash the particles using
large amounts of organic
solvent (e.g., ether, ethanol,
acetone).
25
Large amounts of organic solvents are required
to obtain nanospheres free of any oil or
residues.
It is very difficult to produce small nanospheres
(<500 nm) with narrow-size distributions, due to
the instability of the emulsion prior to hardening
by heat or crosslinking.
Disadvantages of this technique:
The purification step may cause particle wastes.
The hardening step by heat denaturation may be
harmful to heat-sensitive drugs. This can be
avoided by the use of a crosslinking agent.
26
Preparation of nanospheres by thermal denaturation of Preparation of nanospheres by thermal denaturation of albuminalbumin
27
Phase Separation-Based Methods in an Aqueous Medium
The particles are formed in an aqueous medium by a
phase
separation process and are stabilized by cross linking
with
glutaraldehye.
Gelatin and albumin nanospheres can be produced
by the slow addition of a desolvating agent (neutral
salt or alcohol) to the protein solution to the form
protein aggregates
The nanospheres are obtained by crosslinking of
these aggregates with glutaraldehyde.
28
Preparation of nanospheres by desolvation of Preparation of nanospheres by desolvation of albumin.albumin. 29
The major disadvantage of this
technique is the necessity for
using hardening agents
(glutaraldehyde) that may react
with the drug and may cause
toxicity to the nanoparticle
formulations.
30
Nanospheres Prepared From Synthetic PolymersNanospheres Prepared From Synthetic Polymers
Examples of synthetic polymers used for the
preparation
of nanospheres:
Polylactic acid (PLA), poly(glycolic acid) (PGA),
polylactic-co-glycolic acid) (PLGA), poly(e-
caprolactone)
(PCL), and poly(Polyhydroxybutyrate) (PHB).
These polyesters polymers exhibit biodegradability
and biocompatibility.
Under physiological conditions, they are degraded
into safe products as glycolic acid and lactic acid.
31
Polyesters nanoparticles can be produced using two
different methods.
The method is based on the emulsification of an
organic solution of the polymer (chloroform,
methylene chloride, ethyl acetate), in an aqueous
phase (o/w emulsion) containing surfactants (e.g.,
polysorbate, poloxamer, sodium dodecyl sulfate).
The extraction of the solvent from the nanodroplets
is achieved by evaporation of the organic solvent at
room temperature under stirring.
Emulsification-Based Methods.
32
Emulsification-solvent evaporation method 33
A second method is based on the direct
precipitation of the solubilized polymer by salting
out process
Two different salting-out agents, magnesium
chloride and magnesium acetate, were used,
providing an acidic or a basic aqueous phase,
respectively.
Although the salting-out process has proved
suitable for
the production of large quantities of highly drug-
loaded
nanospheres, the use of large amounts of salts
may raise a problem concerning compatibility with
active compounds.
34
Salting-out process 35
This method allows nanospheres to be obtained
without prior emulsification.
This technique involves the use of an organic solvent
that is completely miscible with the aqueous phase,
typically (acetone, ethanol or methanol).
In this case, the polymer precipitation is directly
induced in an aqueous medium (non solvent), by
progressive
addition under stirring of the polymer solution.
This method is limited to drugs that are highly
soluble
in polar solvents, but only slightly soluble in water
(e.g.,
indomethacin).
Direct Precipitation-Based MethodDirect Precipitation-Based Method
36
Direct precipitation methodDirect precipitation method 37
There are some requirements for nanoparticles
intended to be used as pharmaceutical dosage forms
in humans:
(1)to be free of any potentially toxic impurities
(2)to be easy to store and to administer
(3)to be sterile if for parenteral administration.
38
Purification.
Depending on the preparation method, various
toxic impurities can be found in the
nanoparticulate suspensions including:
organic solvents, residual monomers,
polymerization initiators, electrolytes, surfactants,
stabilizers, and large polymer aggregates.
The necessity for and degree of purification are
dependent on the final purpose of the formulation
developed.
39
For example, the stabilizer PVA,
frequently used to prepare
polyester nanoparticles, is not
acceptable for parenteral
administration, whereas it is not so
critical for oral and ocular
administration. Polymer aggregates can be easily removed by
simple filtration.
The removal of other impurities requires more
complicated procedures as gel filtration, dialysis,
and ultracentrifugation. 40
However, these methods are incapable of
eliminating molecules with high molecular weight.
Using cross-flow filtration technique, the
nanoparticle suspension is filtered through
membranes, with the direction of the fluid being
tangential to the surface of the membranes to
avoid the clogging of the filters.
It was shown that by using a microfiltration
membrane (porosity of 100 nm), nanoparticles
produced by the salting out process could be
purified of the salts.41
Main Methods for the Purification of Nanoparticles on the Laboratory Scale
42
Freeze-drying (lyophilization) represents one of the
most useful methodologies to ensure the long-term
conservation of polymeric nanoparticles
This technique involves the freezing of the
suspension and the elimination of its water content
by sublimation under reduced pressure, where
nanoparticles are obtained in the form of a dry
powder that is easy to handle and to store. Freeze-
dried nanoparticles are usually readily redispersible
in water without modification of their
physicochemical properties
Freeze-drying.
43
Nanocapsules composed of an oily core surrounded
by a tiny polymeric wall tend to aggregate during
the freeze-drying process.
This problem can be solved by desiccating these
systems in the presence of an appropriate
lyoprotective and cryoprotection agent such as
mono- or disaccharides
(e.g., lactose, sucrose, glucose).
The mechanisms by which sugars protect
nanoparticles
during freeze-drying is that during freezedrying
sugars may interact with the solute of interest (e.g.,
liposome, protein) through hydrogen-bonding. 44
It has to be kept in mind that the addition of sugar
may affect the isotonicity of the final
nanoparticulate suspension, and that a subsequent
step of tonicity adjustment may be required prior to
any parenteral or ocular administration.
As a result, the solute
might be maintained in a
"pseudo-hydrated“ state
during the dehydrating
step of freeze-drying, and
would therefore be
protected from damage
during dehydration and
subsequent rehydration.
45
Nanoparticles intended to be used parenterally Nanoparticles intended to be used parenterally
are required to be sterile and apyrogenic.are required to be sterile and apyrogenic.
Filtration on 0.22 Filtration on 0.22 μμm m filters is not adequate for filters is not adequate for
nanoparticle suspensions because microorganisms nanoparticle suspensions because microorganisms
and nanoparticles are generally similar in size and nanoparticles are generally similar in size
(0.25-1 (0.25-1 μμm).m).
Sterilization may be achieved, either by using Sterilization may be achieved, either by using
aseptic conditions throughout formulation, or by aseptic conditions throughout formulation, or by
sterilizing treatments such as autoclaving or sterilizing treatments such as autoclaving or γγ--
irradiation.irradiation.
Sterilization
46
The choice of the sterilizing treatment depends on The choice of the sterilizing treatment depends on
the physical susceptibility of the system. the physical susceptibility of the system.
Autoclaving (moist heat sterilization) and Autoclaving (moist heat sterilization) and γγ -
irradiationirradiation
May alter the physicochemical properties of the May alter the physicochemical properties of the
particles in several systems. particles in several systems.
These modifications occur as a consequence of the These modifications occur as a consequence of the
cleavage or cross-linking of the polymeric chains.cleavage or cross-linking of the polymeric chains.
The final formulation would therefore result from a
rational balance between conditions maintaining
the formulation integrity upon sterilization and the
final purpose of the formulation.47
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