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By
SARADA ANEPU
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Microencapsulation is a process by which very tiny droplets or particles of
liquid or solid material are surrounded or coated with a continuous film of
polymeric material.
The product obtained by this process is called as micro particles.
Particles having diameter between 3 - 800µm are known as micro particles or
microcapsules or microspheres.
Particles larger than 1000µm are known as Macroparticles .
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To mask the bitter taste of drugs
To reduce gastric irritations
A liquid can be converted to a pseudo-solid for easy handling and storage
Hygroscopic properties of core materials may be reduced bymicroencapsulation
To reduce their odor and volatility.
Protection to the core materials against atmospheric effects
Separation of incompatible substance
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Generally Micro particles consist of two components
a) Core material
b) Coat or wall or shell material
1.Microcapsules: The active agent forms a core surrounded by an inert
diffusion barrier.
Microcapsules have well defined core and well defined envelope
2.Microspheres: The active agent is dispersed or dissolved in an inert polymer
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RELEASE MECHANISMSDisruption of the coating by pressure, shear or abrasive force
Permeability change brought about by enzymatic fluid
The wall melts away from the core releasing the core in an environment such as
that occurring during baking
The core diffuses through the wall at a slow rate due to the influence of an
exterior fluid such as water or by an elevated temperature
Rate of release depends on
Permeability of coating material to extraction fluid
Dissolution rate of core
Coating thickness
Concentration across the membranes
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o The material to be coatedo It may be liquid or solid or gas.
o Liquid core may be dissolved or dispersed
materialCOMPOSITION OF CORE MATERIAL:
o Drug or active constituent
o Additive like diluentso Stabilizers
o Release rate enhancers or retardants
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Inert substance which coats on core with desired
thickness
IDEAL CHARACTERISTICS:o Capable of forming a film cohesive with core
materialo Chemically compatible with the core materialo Should be stable, non reactive & cheapo Provide desired coating properties like strength,
flexibility& impermeability
COMPOSITION OF COATINGo Inert polymer o Plasticizer o Coloring agent
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Non biodegradable
Acrolein
Epoxy polymers
Biodegradable
Polyesters
Poly ortho esters
Poly anhydrides
Polyphosphazenes
SyntheticProteins
Albumin
Gelatin
collagen
Carbohydrates
Starch
AgaroseCarragreen
Chitosan
Natural
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Physical
• Pan Coating• Fluidized bed
• Multi orifice-centrifugalprocess
• Spinning disc• Spray drying
Physicochemical
• Coacervation• Single
emulsion
• Doubleemulsion
• RESS method• SAS method
Chemical
• SolventEvaporation
• Interfacialpolymerisation
• Matrix
Polymerisation
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Pan Coating
Air suspension
Centrifugalextrusion
Spinning disc
Spray drying
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Two steps;
Preparation of core Coating procedure
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Air suspension process:
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Multiorifice-centrifugal process, developed by the SouthwestResearch Institute as a mechanical process for producingmicro-capsules that utilizes centrifugal forces to hurl a corematerial particle trough an enveloping microencapsulationmembrane thereby affecting mechanical microencapsulation.
The factors that affect process include the rotational speed of the cylinder, the flow rate of the coating and core materials andthe concentration, viscosity and surface tension of the corematerial.
This process is capable of producing the microencapsulation of the liquids and solids of varied size ranges, by applying thedifferent coating materials.
The encapsulated product can be supplied as slurry in thehardening media
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In rotational suspension separation, or thespinning disk method internal phase is dispersedinto the liquid wall material and the mixture isadvanced onto a turning disk.
Droplets of pure shell material are thrown off of the rim of the disk along with discrete particles of core material enclosed in a skin of shell material.
After having been solidified by cooling, themicrocapsules are collected separately from theparticles of shell material
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An emulsion is prepared by dispersing thecore material, immiscible with water, intoa concentrated solution of wall materialuntil the desired size of oil droplets areattained.
The resultant emulsion is atomized into aspray of droplets by pumping the slurrythrough a rotating disc into the heatedcompartment of a spray drier.
There the water portion of the emulsion isevaporated, yielding dried capsules of variable shape containing scattered drops
of core material. The capsules are collected through
continuous discharge from the spraydrying chamber
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Coacervation
Single emulsionDouble emulsion
RESS method
SAS method
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Polymeric
Membrane
DropletsHomogeneous
Polymer SolutionCoacervate
Droplets
PHASE
SEPARATION
MEMBRANE
FORMATION
1.Formation of three immiscible phases
2.Deposition of coating
3.Rigidization of coating.
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Deposition of coating
This step consits of depositing liqudpolymer on core
Deposition ocuurs onthe interface which ispromoted by decrease
in interfacial energy
Rigidization of coating
Rigidisation of coatingoccurs by
thermal cross linking or desolvation technique
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Natural polymers are
dissolved in aqueous
medium followed by
dispersion in aqueousnon aqueous medium
For dispersion cross
linking is carried out byheat or chemical
agents
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Involves preperation of
multiple emulsions,
water soluble drugs
Primary emulsionprepared subjected to
homogenisation
Aq. Solution of polyvinyl alcohol added
At reduced pressure
solvent is removed
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Pressurized supercritical
solvent containing the shellmaterial and the active
ingredient is released througha small nozzle
The abrupt pressure drop
causes the desolvation of the
shell material and theformation of a coating layer
around the active ingredient.
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This process is also called supercriticalfluid anti-solvent (SAS) method. Wheresupercritical fluid is added to a solutionof shell material and the activeingredients and maintained at highpressure.
This leads to a volume expansion of thesolution that causes super saturationsuch that precipitation of the soluteoccurs.
Thus, the solute must be soluble in the
liquid solvent, but should not dissolve inthe mixture of solvent and supercriticalfluid.
On the other hand, the liquid solventmust be miscible with the supercriticalfluid.
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Solvent Evaporation
Interfacial polymerization
Matrix Polymerization
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Polymer
+ Volatile organic solvent
Organic Polymeric Phase
Formation of Oil-in-Water
Emulsion
Solvent Evaporation
Particle Formation by
Polymer Precipitation
RECOVERY OF POLYMERIC
MICROPARTICLES
Temperature increase
Active
Ingredient
Addition into an aqueous
phase (+o/w stabilizer)
SOLVENT EVAPORATIONS
Step 1:
Formation of a solution/dispersion of
the drug into an organic polymer
phase.
Step 2:
Emulsification of the
polymer phase into an aqueous phase
containing a suitable stabilizer, thus,forming a o/w emulsion.
Step 3:
Removal of the organic
solvent from the dispersed phase by
extraction or evaporation leading to
polymer precipitation and formationof the microspheres.
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Reaction of monomeric
units
Drug is dispersed in thepolymeristion mixture
Alcoholic solution isused as initiator
Polymers precipitate
Microparticles
recovered
Drug
Addition of the alcoholic solution
of the initiator (e.g., AIBN)
8 hrs Reaction time
Monomer(s) (e.g. acrylamide, methacrylic acid)
+ Cross-linker (e.g. methylenebisacrylamide)
Alcohol
T (reaction) = 60 °C
Nitrogen Atmosphere
Preparation of the
Polymerization Mixture
Initiation of
Polymerization
Monodisperse Latex
Formation by Polymer
Precipitation
RECOVERY OF POLYMERIC
MICROPARTICLES
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Proceeds with reaction of monomers at theinterface between two immisible liqud phases toform a film of polymer which envelops dispersedphase
One monomer is dissolved and other is dispersedContinuous phase is usually aqueous in which 2nd
monomer is emulsified
Monomers at either phase diffuse rapidly andpolymerise at interface of core particles
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In a number of processes, a core material isimbedded in a polymeric matrix duringformation of the particles.
A simple method of this type is spray-drying, inwhich the particle is formed by evaporation of the solvent from the matrix material.
The solidification of the matrix also can becaused by a chemical change.
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Process Coating material Suspended medium
Interfacial polymerisation Water-soluble andinsoluble monomers
Aqueous/organic solvent
Complex coacervation Water-solublepolyelectrolyte
Water
Coacervation Hydrophobic polymers Organic solvent
Solvent evaporation Hydrophilic orhydrophobic polymers
Organic or water
Spray drying Hydrophilic orhydrophobic polymers
Air, nitrogen
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Stability testing
Size of microcapsules- Sieving Method
Amount of drug present In microcapsules
Viscosity of polymer solutions
Dissolution test- In vitro drug release
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Separation of the microspheres into various sizefractions can be determined by using amechanical sieve shaker
The sieves (20, 30, 45, 60 and 80 mesh) arearranged in the order of decreasing aperturesizere shaken for a period of about 10 min, and
then the particles on the screen are weighed
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The surface morphologies of microspheresare examined by a scanning electronmicroscope
Nature of the microspere is examinedThe microspheres are mounted onto a copper
Cylinder by using a double-sided adhesive
tape.
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Bulk density tapped density are determined
The Hausner ratio of the microcapsules is
determined by the following relationshiphr = ρ tapped/ρ bulk
Where ρ tapped is tapped density
ρ bulk is bulk density.
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The absolute viscosity, kinematic viscosity,and the intrinsic viscosity of the polymersolutions in different solvents can be
measured by a U-tube viscometerThe polymer solutions are allowed to stand
for 24 h prior to measurement to ensure
complete polymer dissolution
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Standard USP or BP dissolution apparatus areused to study in vitro release profiles
Dissolution medium used for the study varied
from 100-500 ml and speed of rotation from50-100 rpm.
Dissolution medium is decided from the drug
being encapsulated
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Targeted drug delivery to Peyer’s patch
Live cell encapsulation
Bioadhesive microparticles show enhanced oralbio availability of insulin, dicumarol
DNA vaccines with prolonged immunoresponses
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Ansel,H.C., Pharmaceutical dosage form anddrug delivery system.
Lehman Leon, Lieberman A. Herbert and
KanigL.Josep. The Theory and Practice of IndustrialPharmacy
S.P.Vyas and R.K.Khar, Targeted
andControlled drug delivery
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