Microencapsulation

Sadgir . Pooja. B.
M. Pharm.
(pharmaceutics)
1

CONTENTS-
Introduction .
Advantages of microencapsulation technique.
Application of microencapsulation.
Material use for coating the drug.
Properties of coating material.
Microencapsulation techniques.
Kinetics properties of microencapsulation.
Characterization of microcapsules.
Evaluation of microencapsulation.
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INTRODUCTION
Microencapsulation is the process in which small droplets or particles of liquid or
solid materials are surrounded or coated by a continuous film of polymeric
materials.firstly,the microencapsulation procedure was discovered by Bungen burg
de jon and kan in 1931 and which included the preparation of gelatin spheres and
the use of a gelatin coacervation process.microencapsulation process helps in
converting the liquids to solids,changing the collidal and surface properties,
providing enviromental protection.
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Advantages of microencapsulation techniques-
1.The important resason for microencapsulation is found to be either for
sustained or prolonged drug release .
2.This technique has been widely used for masking the taste and odour of
many drugs to improve patient compliance .
3.The drugs,which are sensitive to oxygen ,moisture or light,
can be stabilized by microencapsulation.
4.Incompatability among the drugs can be prevented by
microencapsulation.
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Fig(a)-Mononuclear Fig(b)-Multinuclear
Scanning electron (Microsphers)
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Materials Used for coating the drug-
Two types of material are used as follows .
1.Core material.
2.Coating material.
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1.Core material-
The coare material is defiend as the specific material to be coated which can be
liquid or in nature.The composition of the core material can be varied. The liquid
core can include dispersed and dissolved materials. The solid core may be active
constituents , stabilizerdiluents, exicipients, and release-rate retardants or
accelerators.The ability to vary the core material composition provides a definite
flexibility and utilization of these chacteristics which often allows effectual design
and develoopment of the desierd microcapsule properties.
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2.Coating materials-
The coating material should be capable of forming a film that is cohesive
with the core material. The coating material should be chemically
compatible and non -reactive with the core material and provide the desired
coating properties ,such as stength, flexibility, impermeability, optical
properties, andstability.
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Properties of coating materials-
1.Stabilization of coare material.
2.Inert toward acctive ingredients.
3.Controlled release under specific conditions.
4.Film-forming, pliable, tastelee, stable.
5.Non-hygroscopic, low viscosity, and economical.
6.Soluble in anaqueous media or solvent.
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Example of coating material
The coating material is most important in the preparation of
microencapsulation .
1.Water soluble resins:- Gelatin, gum arabic,polyvinylpyrrolidone,
methylcellulose ,carboxy methylcellulose , PVP etc.
2.Water insoluble resins:- Ethylcellulose, polyamide(nylon) etc.
3.Waxes and lipids:-Paraffin, beeswax , stearic acid etc.
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Microencapsulation Techniques:-
Air suspension technique
Coacervation phase sepration technique
Spray drying and spray congealing method
Multiorifice centrifugal process
Pan coating method
Solvent evaporation techniques
Polymerization
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 Air suspension technique -
Fig- Wurster air suspension apparatus
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Working-
Air-suspension coating of particles by solutions or melts give a better control
and flexibility.the particles are coated, while being suspended in an upward-
moving air stream. they are supported by a perforated plate having diffferent
patterns of holes inside and outside a cylindrical insert. just sufficient air is
permitted to rise through the outer annular space to fluidize the settling
prticles. most of the rising air flows inside the cylindercausing the particles to
rise rapidly. at the top, as air stream diverges and slow, they settle back onto
the bed and move downward to repeat the cycle.
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The variables that can affect the air suspension process are as
follows:-
1. Concentration of the coating material or if in solution form then melting
point.
2.Solubility, surface area, density, melting point and volatility.
3. Temperature of air stream.
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 Coacervation-phase separation techinque :-
Fig:-coacervation phase separation technique
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Schematic representation of the coacervation process -
a)Core material dispersion in solution of shell polymer .
b)Separation of coacervate from solution .
c)Coating of core material by microdroplets of coacervate .
d)Coalescence of coacervaate to form continuous shell around core particles .

Coacervation-phase separation consists of three steps carried out
under continuous agitation:-
1.Formation of three immiscible chemical phases:- liquid manufacturing
vehicle phase, core material phase and coating material phase.
2.Deposition of coating:- core material is dispersed in the coating polymer
solution. Coating polymer material coated around core. Deposition of liquid
polymer coating around core by polymer adsorbed at the interface formed
between core material and vehicle phase.
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3.Rigidization of coating:- coating material is immiscible in vehicle phase and is
made rigid. This is done by thermal, cross-linking, or dissolution techniques.
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 Spray drying and spray congealing -

Spray-congealing –
 The coating solidification is effected by thermally congealing a molten
coating material .
Removal of the non-solvant or solvent from the coated product by sorption ,
extraction or evaporation technique .
Spray –drying –
The coating solidification effected by rapid evaporation of solvent in which
coating material is dissolved .

 Pan coating
 The pan coating process, widely used in the pharmaceutical industry, is among
the oldest industrial procedures for forming small, coated particles or
tablets.
 Suitable for relatively large particles .
 Solid particles greater than 600 microns in size are generally coated by pan
coating .
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 Solvent evaporation process -
Core material
Dissolved or dispersed
Coating polymer solution
With agitation
Form core coating material mixture
Liquid manufacturing vehicle phase
Heating (if necessary )
Evaporation of polymer solvent
Microencapsulation ( matrix type )

 Polymerization -
 A relatively new microencapsulation method utilizes polymerization
techniques to form protective microcapsules coating in situ .
 The reaction of monomeric units located at the interface existing between a
core material substance and a continuous phase in which core material is
dispersed .
 The core material supporting phase is usually a liquid or gas , and therefore
the polymerization reaction occurs at a liquid –liquid , liquid –gas , solid –
liquid , solid –gas interface .

Kinetics of the drug release from microencapsulation:-
Major mechanism of drug release from micro -capsules includes Difusion,
dissolution, osmosis,and erosion.
1)Diffusion:-
Diffusion is the most common mechanism of drug release in which the
dissolution fluid penetrates the shell and then the core material comes in contact
with the disssolutin fluid and lick out the through the inerstital channels or
pores. Bascally rate of pentration, and the rate at which the dissolved drug
escape fro the microcapsule.
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The release of drug from the microcapsule depends on the dissolution rate
of polymer coate, and the solubility of the coat in the dissolution fluid.
Generally the solubility in the dissolution fluid and thickness of coat
influence the release rate.
3) Osmosis-
Another method of drug release is through osmosis.The essential
requirement of osmosis is semi-permeable membrane and a microcapsule
polymer coat serve the purpose.
2)Dissolution
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As the process progresses an osmotic pressure is created between the
outside and inside membrane of microcapsule which results in the release
of drrug through small pores.
4) Erosion-
Erosion of coat generally occurs due to the pH or enzymatic hydrolysis
and caues the release of drug with ccertain coat materials like beeswax,
stearyl alcohol.the drug release from icrocapsules has become
complicated because of the diversity in the physical forms of
microcapsules with shape, size and arrangement of the coat and core
materials.
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Physicochemical propertise:-
Core materials like partition coefficient diffusibility and solubility and
coating materials like variable porosity, thikness and interness make it
difficult to model drug release .
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Evaluation of microencapsulation :-
1. Characterization
2. Sieve analysis
3. Morphology of microsphere
4. Polymer solubility in the solvent
5. Viscosity
6. Density determination
7. Bulk density
8. In vitro methods
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Reference
Dr. D T. Bviskar , Dr. D.K.jain “Novel Drug Delivery System” 1st
ed,
july 2012,published by Nirali Prakashan.p.-3.1-3.2,3.15-3.16
Jain NK.Controlled and Novel Drug Delivery. 1st
ed.CBS Publisher
1997.p236-37
Leon L,Herbert AL,The therory and practice of industrial pharmacy.2rd
ed. Vaghese Publishing House;1996.p-412-28.
Microencapsulation :a review international journal of pharmaceutical
sciences review and research volume 1, marches- April 2010 .
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Microencapsulation

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