Microencapsulation

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Microencapsulation
by Sampada Tamhankar

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Contents
1.1 DEFINITION, NEED, CONCEPTS OF CORE AND COAT
1.2 METHODS OF MICROENCAPSULATION
1.3 EVALUATION OF MICROCAPSULES
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1.1 DEFINITION
 Microencapsulation is a means of applying
relatively thin coatings to small particles of
solids or droplets of liquids and dispersions
 Microencapsulation is a process by which solids,
liquids and gases may be enclosed in
microscopic particles by formation of thin coats
around the core substance.
 Size of a microcapsule ranges from 50 nm to 2
mm
CORE
COATING

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1.1 NEED/ REASONS FOR MICROENCAPSULATION
 To overcome the problems of
conventional therapy
 To enhance the therapeutic
efficacy of given drug
 To retard quick evaporation of
volatile core material
 To prevent vitamins getting
degraded due to oxidation
 For safe handling of toxic
materials
 To ease handling of sticky
and greasy material core
 To prevent radio-active
material from chemical
attack
 To achieve controlled or
targeted release of drug
 To mask the odour and taste
of unpalatable drugs

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1.1 CONCEPTS OF CORE AND COAT
 Core can be defined as the material which is to be coated
 The core can either be solid, liquid or gaseous material
 The liquid core composition may be varied considering
that the solute particles have been dissolved or dispersed
 The solid core can be single substance or mixture of
active constituents along with stabilizers, diluents,
excipients, etc.
CORE

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 Coat is the material which applied over the core material during
encapsulation
 Selection of coating material decides the physical and chemical
properties of the resultant microcapsules
 While selecting a coating material following are the parameters that are
to be taken under consideration including:
 Stability, volatility, release characteristics, environmental condition,
etc.
COAT

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1.1 COATING MATERIAL
Chemically
modified
carbohydrates
Poly acryl dextran,
Poly acryl starch
Proteins
Albumins,
Gelatin,
Collagen
Carbohydrates
Starch,
Carrageenan
POLYMERS
Polyanhydrides,
Lactides,
Nylon,
Polyethylene,
Teflon,
Epoxy polymers,
Acrolein
SYNTHETIC NATURAL

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 The type of polymer used in
microencapsulation is either
hydrophilic/ hydrophobic or a
combination of both
 Various coating materials that are
widely used are:
Gelatin
PVA (polyvinyl alcohol)
Ethyl cellulose
CAP (cellulose acetate phthalate)
single particle or clusters of particles
 After isolation from the liquid
manufacturing vehicle and drying, the
material appears as a free flowing
powder
 The powder is suitable for formulation
as:
compressed tablets
hard gelatin capsules
suspensions and other dosage
forms by Sampada Tamhankar

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MONONUCLEAR POLYNUCLEAR MATRIX
Contain the shell
around the core
Many cores enclosed
within the shell
Distributed homogeneously
in the shell material
TYPES OF MICROCAPSULES
RESERVOIR

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RELEASE MECHANISMS
 Microencapsulation aims at creating a coat wall around the core
 This wall is supposed to be ruptured during the time of use
 The rupturing occurs through various release mechanisms :
By pressure or shear stress
By melting the wall
By enzyme attack
By chemical reaction
By hydrolysis or slow disintegration
By dissolving it under particular conditions, as in the case of an enteric drug
coating by Sampada Tamhankar

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2.1 METHODS OF MICROENCAPSULATION
1) Phase Separation Coacervation
2) Wurster Process
3) Spray Drying
4) Interfacial Polymerization
5) Multiorifice Centrifugal Process
6) Pan Coating
7) Solvent Evaporation
8) Extrusion And Spheronisation

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1) PHASE SEPARATION COACERVATION
Process:
It consists of three steps:
1) Formation of three immiscible chemical
phases – Liquid manufacturing phase,
core material phase, coating material
phase.
2) Deposition of coating: Liquid polymer
deposits on core material since it is
immiscible polymer
3) Rigidisation of coating: By thermal cross
linking and desolvation techniques.
• Various coacervation phase separation
methods are methods are:
a) Temperature Change Method
b) Incompatible Polymer Addition Method
c) Non Solvent Addition Method
d) Salt Addition Method
e) Polymer- Polymer Interaction

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DRUG
Phase separation
Formation of three
immiscible phases
COACERVATE DROPLET
RIGIDISATION
DUE TO
COOLINGPOLYMERIC
MEMBRANE
SEPARATION
SOLVENT
EXTRACTION

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A. Temperature change method
• Microencapsulation takes place by reducing temperature E.g. 2% Ethyl cellulose is
dispersed in cyclohexane . The mixture is heated to boiling point to form a
homogenous polymer solution.
• Core material e.g. paracetamol is dispersed in a solution ratio of coating material to
core material is 1:2. Mixture is allowed to cool with continuous stirring This effects
phase separation followed by coacervation.
• On further cooling gelation and solidification coating takes place. Microencapsulated
product is collected from cyclohexane by filtration, decantation and centrifugation
technique.

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2) WURSTER PROCESS (fluidized bed coaters)
Only solid particles or porous particles can be encapsulated.
Process:
1) A bed or column of solid particles is suspended in a moving
gas stream.
2) A liquid coating solution is sprayed into the individual
particles.
3) Coating formulation is dried either by solvent evaporation or
cooling.
4) This coating and drying sequence is repeated until a desired
coating thickness has been achieved.
5) The coated particles then fall back down to the bottom of unit
where a fresh coating is applied.
Wurster Process

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2) WURSTER PROCESS (fluidized bed coaters)
Advantages:
 Applicable for
wide range of
materials
 E.g. Enteric
coating
 Since
multistage
operation
defects in
coating can be
minimised.

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3) SPRAY DRYING AND RELATED PROCESSES
Advantages:
 Since no cross linking it readily disperses in
water.
 Low bulk density of microcapsules.
 Cost efficient process.
Disadvantages:
Organic solvents are flammable. Hence, they
can not be used in spray drying.

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3) SPRAY DRYING
The core material is mainly liquid
Process:
1) Core is dispersed or emulsified with coating
material
2) Shell material is water soluble polymer such as
gum Arabic or modified starch.
3) The resulting solution is fed as droplets into
heated chamber of a spray drier.
4) Rapid evaporation of solvent takes place and
droplets are dehydrated in heated chamber
5) Dry capsules fall at bottom are of size is 10 to
300 µ. by Sampada Tamhankar

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3) SPRAY CONGEALING METHOD
• Molten coating material is thermally
congealed
• Hot mixture is spread into cool air
stream
• Using this method waxes, fatty acids,
fatty alcohols, polymers and sugars
that are solid at room temperature but
meltable at reasonable temperature
can be coated
Spray congealing depends upon:
Atomising wheel velocity, Speed rate, Viscosity

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4) INTERFACIAL POLYMERIZATION
1) The
microcapsules
will be formed at
the surface of
the droplet
2) The substances
used are
multifunctional
monomers
3) These will be
used either
individually on in
combination

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4) INTERFACIAL POLYMERIZATION
Process:
1) The multifunctional monomer dissolved in liquid core material. i.e. they will
be dispersed in aqueous phase containing dispersing agent
2) The core material will be added in the organic phase and then mixed with
aqueous phase
3) Now rapid mixing of these two phases will occur reducing the interfacial
tension
4) This will lead to the polymerization of coating material from aqueous
phase with the core material in organic phase forming the microcapsules
which will be deposited at the bottom

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5) MULTIORIFICE CENTRIFUGAL PROCESS
This is a mechanical process for production of microcapsules which was developed by
SWRI (South West Research institute). It utilises centrifugal force to cast a core material
particle through enveloping microencapsulation membrane.
Process:
 Three circumference groves are located within the cylinder.
 In intermediate grove orifice spaces closely and circumferentially around the cylinder.
 Carry the coating material in molten or solution form.
 Coating material under centrifugal force imparted by cylinder. Rotation flows outward.
 The embryonic microcapsules upon leaving the orifices are hardened congealed or
voided of coating solution.

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5) MULTIORIFICE CENTRIFUGAL PROCESS
The processing variables
are:
1. Rotational speed of
cylinder
2. Flow rate of core and
coating material.
3. Viscosity and surface
tension of coating
material.
4. Concentration of coating
material

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6) PAN COATING
• Suitable for solid particles greater than
600 microns in size are generally
coated by pan coating
• Extensively employed for the
Preparation of controlled release beads

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6) PAN COATING
Process:
• In this method the coating material is applied as a solution or as an
atomized spray to the desired solid core material in the coating pan
• To remove the coating solvent, warm air is passed over the coated material
to remove the excess as the coatings are being applied in the coating pans
• In some cases, final solvent removal is accomplished in drying oven
• Coating operation is repeated 3 to 4 times. Last coating of talc is applied.
The pellets are rolled with dry air. The excess of talc is removed by
vacuum.

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7) SOLVENT EVAPOARTAION
• Solvent evaporation techniques are carried out in a liquid manufacturing vehicle
(O/W emulsion) which is prepared by agitation of two immiscible liquids.
• For mixing the most common method is the use of a propeller style blade
attached to a variable speed motor

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7) SOLVENT EVAPOARTAION
• Process:
• The process involves dissolving microcapsule coating (polymer) in a volatile
solvent which is immiscible with the liquid manufacturing vehicle phase.
• A core material (drug) to be microencapsulated is dissolved or dispersed in the
coating polymer solution
• With agitation, the core – coating material mixture is dispersed in the liquid
manufacturing vehicle phase to obtain appropriate size microcapsules
• Agitation of system is continued until the solvent partitions into the aqueous
phase and is removed by evaporation
• This process results in hardened microspheres which contain the active moiety

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8) EXTRUSION AND SPHERONISATION
CORE COAT

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CO EXTRUSION
• A dual fluid stream of liquid core and shell
materials is pumped through concentric tubes
and forms droplets under the influence of
vibration.
• The shell is then hardened by chemical cross
linking, cooling, or solvent evaporation.
• Different types of extrusion nozzles have
beendeveloped in order to optimize the process

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1. PARTICLE SIZE
a) LASER DIFFRACTOMETRY
 Approximately 30 mg microparticles
is redispersed in 2–3 ml distilled
water, containing 0.1% tween 20 for 3
min, using ultrasound.
 Then transferred into the small
volume recirculating unit, operating at
60 ml/ s.
 Then the microparticle size is
determined by laser diffractometer.

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b) SIEVE ANALYSIS
1) Separation of the microspheres into various size fractions
can be determined by using a mechanical sieve shaker.
2) A series of five standard stainless steel sieves (20, 30, 45,
60 and 80 mesh) are arranged in the order of decreasing
aperture size.
3) Five grams of drug loaded microspheres are placed on the
uppermost sieve.
4) The sieves are shaken for a period of about 10 min, and
then the particles on the screen are weighed.

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2. MORPHOLOGY OF MICROSPHERES
Two methods can be used :
a) SCANNING ELECTRON MICROSCOPE –
The surface morphologies of
microspheres are examined by a
scanning electron microscope.
b) MULTIMODE ATOMIC FORCE
MICROSCOPE -
A Multimode Atomic Force Microscope
form Digital Instrument is used to study
the surface morphology of the
microspheres. by Sampada Tamhankar

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3. VISCOSITY OF THE POLYMER
SOLUTIONS
• The absolute viscosity, kinematic viscosity,
and the intrinsic viscosity of the polymer
solutions in different solvents can be
measured by a U-tube viscometer.
• The polymer solutions are allowed to stand
for 24 h prior to measurement to ensure
complete polymer dissolution.

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4. DENSITY DETERMINATION
• The density of the microspheres can be measured by using a multi volume
pycnometer.
• Accurately weighed sample in a cup is placed into the multi volume
pycnometer.
• Helium is introduced at a constant pressure in the chamber and allowed to
expand. This expansion results in a decrease in pressure within the chamber.
• Two consecutive readings of reduction in pressure at different initial pressure
are noted.
• From two pressure readings the volume and density of the microsphere
carrier is determined. by Sampada Tamhankar

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5. DISSOLUTION
 Standard USP or BP dissolution
apparatus have been used to
study in vitro release profiles.
 Dissolution medium used for
the study varied from 100-500
ml and speed of rotation from
50-100 rpm.

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THANK YOU
bySampadaTamhankar

Microencapsulation

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