Microencapsulation

CONTENTS
• Introduction
• Reasons for Microencapsulation
• Release Mechanisms
• Coating Materials
• Coating Material Properties
• Techniques to Manufacture
• Application
• References

Defination
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.
Microencapsulation may be defined as the process of surrounding or
enveloping one substance within another substance on a very small scale,
yielding capsules ranging from less than one micron to several hundred
microns in size.”
It is mean of applying thin coating to small particle of solid or droplet of
liquid & dispersion.
Microencapsulation is a process by which solids,
Liquids or even gases may be enclosed in microscopic
particles by formation of thin coatings of wall material
around the substances
INTRODUCTION

• Particle size: 50-5000 micron.
• 2 phases: a) Core material
b) Coating material
The product obtained by this process is called as micro particles,
microcapsules, microsphere, coated granules, pellets..
Particles having diameter between 3 - 800µm are known as micro
particles or microcapsules or microspheres.
 Particles larger than 1000µm are known as Macroparticles .

A well designed controlled drug deliverysystem
- can overcome some of the problems of conventional therapy.
- enhance the therapeutic efficacy of a given drug.

To obtain maximum therapeutic efficacy, drug is to be
delivered :
-to the target tissue
-in the optimal amount
-in the right period of time
there by causing little toxicity and minimal side effects.
One such approach is using microspheres as carriers for drugs.
Microspheres are characteristically free flowing powders
consisting of proteins or synthetic polymers
 biodegradable in nature
particle size less than 200 μm.

Microspheres Formulated Microsphere
Red one’s are R.B.C
Purple one’s are microspheres

REASONS FOR MICROENCAPSULATION
1. To protect reactive substances from the environment,
2. To convert liquid active components into a dry solid system,
3. To separate incompatible components for functional reasons,
4. To protect the immediate environment of the microcapsules from the
active components.
as in isolating vitamins from the5. Isolation of core from its surroundings,
deteriorating effects of oxygen.
6. retarding evaporation of a volatile core.
7. improving the handling properties of a sticky material.
8. isolating a reactive core from chemical attack.
9. for safe handling of the toxic materials.
10. to get targeted release of the drug
11. To control release of the active components for delayed (timed) release or
long-acting (sustained) release,
12. The problem may be as simple as masking the taste or odor of the core,
13. To Increase of bioavailability,
14. To produce a targeted drug delivery,
15. Protects the GIT from irritant effects of the drug,
16. Extension of duration of activity for an equal level of active agent.

Generally Micro particles consist of two components
a) Core material.
The solid core can be mixture of active constituents, stabilizers,
diluents, excipients and release-rate retardants or accelerators.
b) Coat or wall or shell material
•Compatible, non reactive with core material
•Provide desired coating properties like strength, flexibility,
impermeability, optical properties, non hygroscopicity, tasteless and stable
Fundamental Consideration /Formulation considerations

Core Material
The material to be coated. It may be liquid or solid or gas. Liquid core
may be dissolved or dispersed material.
Composition of core material:
Drug or active constituent
Additive like diluents
Stabilizers

Coating Material
Inert substance which coats on core with desired thickness.
Composition of coating:
 Inert polymer
 Plasticizer
 Coloring agent
 Resins, waxes and lipids
 Release rate enhancers or retardants
ROLE OF POLYMERS :
 Polymers are substances of high molecular weight made up by repeating
monomer units.
 Polymer molecules may be linear or branched, and separate linear or
branched chains may be joined by crosslinks.
Polymers are used widely in pharmaceutical systems as adjuvants,
coating materials and, a components of controlled and site- specific drug
delivery systems

1. Stabilization of core material.
2. Inert toward active ingredients.
3. Controlled release under specific conditions.
4. Film-forming, pliable, tasteless, stable.
5. Non-hygroscopic, no high viscosity, economical.
6. Soluble in an aqueous media or solvent, or melting.
7. The coating can be flexible, brittle, hard, thin etc.
Coating Material Properties

List of coating material
Water soluble
resin
Water insoluble
resin
Wax & lipid Enteric resin
Gelatin, Ethyl cellulose, Paraffin, Shellac,
Gum arabic, Polyethylene, Carnauba wax, Zein,
PVP,
CMC,
Polymethacrylate,
Cellulose nitrate,
Bees wax,
Stearic acid,
Cellulose acetate
phthalate.
Methyl cellulose, Silicones. Stearyl alcohol.
Arabinogalactan,
Polyvinyl
acrylate,
Polyacrylic acid.

Core
Material
Characteristic
Property
Purpose of
Encapsulation
Final Product
Form
Aspirin Slightly water-
soluble solid
Taste-masking; sustained
release; reduced gastric
irritation; separation of
incompatibles
Tablet or
capsule
Vitamin A
Palmitate
Nonvolatile
liquid
Stabilization to oxidation Dry powder
Isosorbide
dinitrate
Water soluble
solid
sustained release Capsule
Table: Properties of Some Microencapsulated Core Materials.

ADVANTAGES:
 To Increase of bioavailability
 To alter the drug release
 To improve the patient’s compliance
 To produce a targeted drug delivery
the outside To reduce the reactivity of the core in relation to
environment
 To decrease evaporation rate of the core material.
 To convert liquid to solid form & To mask the core taste.
Disadvantages
• It is an expensive process
• Requires skill
• Difficult to obtain continuous and uniform film

Morphology of Microcapsules
The morphology of microcapsules depends mainly on the core material
and the deposition process of the shell.
1Mononuclear (core-shell) microcapsules contain the shell around the
core.
2 Polynuclear capsules have many cores enclosed within the shell.
3Matrix encapsulation in which the core material is distributed
homogeneously into the shell material.
- In addition to these three basic morphologies, microcapsules can also be
mononuclear with multiple shells, or they may form clusters of
microcapsules.

RELEASE MECHANISMS
Even when the aim of a microencapsulation application is the isolation of
the core from its surrounding, the wall must be ruptured at the time of use.
A variety of release mechanisms have been proposed for microcapsules :
by pressure or shear stress.
by melting the wall.
by dissolving it under particular conditions, as in the case of an enteric
drug coating.
by solvent action
by enzyme attack
by chemical reaction
by hydrolysis or slow disintegration.

MICROENCAPSULATION TECHNIQUES:
1. Air suspension techniques(Wurster)
2. Coacervation process
3. Spray drying & congealing
4. Pan coating
5. Solvent evaporation
6. Polymerization
7. Multiorific-centrifugal
8. Extrusion
9. Single & double emulsion techniques
10. Supercritical fluid anti solvent method (SAS)
11. Nozzle vibration technology

Coacervation
Coacervation microencapsulation is the phase separation of one or many
hydrocolloids from the initial solution and the subsequent deposition of the
newly formed coacervate phase around the active ingredient suspended or
emulsified in the same reaction media.
Coacervation is a unique microencapsulation technology because of the very
high payloads achievable up to 99% and the controlled release possibilities
based on mechanical stress, temperature or sustained release.
Coacervation is typically used to encapsulate flavour oil and can also be
adapted for the encapsulation of fish oils, nutrients, vitamins, preservatives and
enzymes.
There are two methods for coacervation are available, namely simpleand
complex processes.
The mechanism of microcapsule formation for both processes is identical,
except for the way in which the phase separation is carried out.
•-

•In simple coacervation : a desolvation agent is added for phase separation.
• whereas complex coacervation involves complexation between two
oppositely charged polymers
The general process consist of 3 steps under continuous agitation:
1. Formation of 3 immiscible chemical phase
2. Deposition of coating
3. Rigidization of coating.
Step: 1) Three immiscible phases are as:
a) Liquid manufacturing vehicle phase
b) Core material phase
c) Coating material phase.
Coating material phase formed by utilizing following methods:
A) Temperature change.
B) By addition of incompatible polymer
C) By non-solvent addition
D) By salt addition
E) Polymer-polymer interaction.

In step 2,
the deposition of the liquid polymer around the interface formed between
the core material and the liquid vehicle phase.
In many cases physical or chemical changes in the coating polymer solution
can be induced so that phase separation of the polymer will occur.
Finally : the prepared microcapsules are stabilized by crosslinking,
desolvation or thermal treatment.
Equipment required for microencapsulation this method is relatively simple;
it consists mainly of jacketed tank with variable speed agitator.

COACERVATION / PHASE SEPARATION
Polymeric
Membrane
Droplets
Homogeneous
Polymer
Solution
Coacervate
Droplets
PHASE
SEPARATION
MEMBRANE
FORMATION
1.Formation of three immiscible phase
2.Deposition of coating
3.Rigidization of coating.

(FLUIDISED BED COATING )
 Inventions of Professor Dale E. Wurster
 Basically the wurster process consists of the dispersing of solid,
particulate core materials in a supporting air stream and the spray-coating
of the air suspended particles.
 Equipment ranging in capacities from one pound to 990 pounds.
 Micron or submicron particles can be effectively encapsulated by air
suspension techniques.
Air Suspension Techniques (Wurster)

 Within the coating chamber, particles are suspended on an upward
moving air stream.
The design of the chamber and its operating parameters effect a
recalculating flow of the particles through the coating zone portion of the
chamber, where a coating material, usually a polymer solution, is spray
applied to the moving particles.

The Wruster Process
This technology is characterized by the
location of a spray nozzle at the bottom of
a fluidized bed of solid particles.
The particles are suspended in the
fluidizing air stream that is designed to
induce a cyclic flow of the particles past the
spray nozzle.
The nozzle sprays an atomized flow of
coating solution, suspension, or other
coating vehicle.
The technology can be used to encapsulate
solid materials with diameters ranging from
near 50µm to several centimeters.
encapsulate vitamins, minerals,
Wruster Process can be used to
and
functional food ingredients.

Air suspension techniques
(WURSTER PROCESS):

• It consist of dispersing the solid particulate core material in supporting air
stream and being coated with coating material (usually polymeric solution)
• In this, the fine core materials are suspended in a vertical current of air and
sprayed with the coating material
• After evaporation of solvent, a layer of encapsulating material is deposited
on core
• Gives improved control and flexibility as compared to pan coating.
• During each pass through the coating zone, the core material receives an
increment of coating material.
• The cyclic process is repeated, perhaps several hundred times during
processing, depending on the purpose of microencapsulation the coating
thickness desired or whether the core material particles are thoroughly
encapsulated.
• The supporting air stream also serves to dry the product while it is being
encapsulated.
• Drying rates are directly related to the volume temperature of the
supporting air stream.
31

 Disadvantage- Agglomeration of the particles to some larger size is
normally achieved.
variables for efficient, effective encapsulation by air suspension
techniques:
1.Density, surface area, melting point, solubility, friability,volatility,
Crystallinity and flow-ability of core the core material.
2.Coating material concentration (or melting point if not a solution).
3.Coating material application rate.
4.Volume of air required to support and fluidizes the core material.
5.Amount of coating material required.
6.Inlet and outlet operating temperatures.

Solvent Evaporation
(Chemical process)
33
 In the case in which the core material is dispersed in the polymer
solution, polymer shrinks around the core.
 In the case in which core material is dissolved in the coating
polymer solution, a matrix - type microcapsule is formed.
 The core materials may be either
water - soluble or
water - insoluble materials.
 A variety of film - forming polymers can be used as coatings.

34
 Used by companies including the
NCR Company,
Gavaert Photo - Production NV, and
Fuji Photo Film Co., Ltd.
eg. Evaluation of Sucrose Esters as Alternative Surfactants in
Microencapsulation of Proteins by the Solvent Evaporation
Method.

35
Core material
Dissolved Or Dispersed
Coating polymer solution
With Agitation
Liquid Manufacturing VehiclePhase
Heating (If necessary)
Evaporation of Polymer solvent
Microencapsulation
Solvent Evaporation process…..

Polymer
+ Volatile organic solvent
Organic Polymeric Phase
Solvent Evaporation
Particle Formation by Polymer
Precipitation
RECOVERY OF POLYMERIC
MICROPARTICLES
Temperature increase
Active
Ingredient
Addition into anaqueous
phase (+o/w stabilizer)
Formation of Oil-in-Water
Emulsion
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 formation
of the microspheres.

Pan coating
 Oldest industrial procedures for forming small, coated particles or tablets.
 The particles are tumbled in a pan or other device while the coating material is
applied slowly.
 Solid particles greater than 600 microns in size are generally considered
essential for effective coating.
 Medicaments are usually coated onto various spherical substrates such as
nonpareil sugar seeds, and then coated with protective layers of various
polymers.
 It is used for preparation of controlled- releasebeads.
 Coating is applied as solution by automized spray to desired solid core
material in coating pan.
 Usually warm air is passed over the coated material as the coating are being
applied in the coating pan.

Figure Pan coater
1. Solid particles are mixed with a dry coating material.
2. The temperature is raised so that the coating material melts and encloses
the core particles, and then is solidified by cooling.
Or,
the coating material can be gradually applied to core particles tumbling in a
vessel rather than being wholly mixed with the core particles from the start
of encapsulation.

 The particles are tumbled in a pan or
other device while the coating
material is applied slowly
 The coating is applied as a solution
or as an atomized spray to the
desired solid core material in the
coating pan
 Usually, to remove the coating
solvent, warm air is passed over the
coated materials as the coatings are
being applied in the coating pans.
 In some cases, final solvent removal
is accomplished in drying oven.

48
Spray Drying and Spray Congealing
Spray Drying:
The coating solidification effected by
rapid evaporating of solvent in which
coating material is dissolved.
Spray Congealing:
The coating solidification is effected
by thermally congealing a molten
coating material. The removal of
solvent is done by sorption,
extraction or evaporation technique. Figure Schematic diagram of a Spray Dryer

49
 In modern spray dryers the viscosity of the solutions to be
sprayed can be as high as 300mPa.s
 Spray drying and spray congealing- dispersing the core
material in a liquefied coating substance and spraying.
 Spray drying is effected by rapid evaporation of a solvent in
which the coating material is dissolved.
The equipment components of a standard spray dryer include
1. an air heater,
2. atomizer,
3. main spray chamber,
4. blower or fan,
5. cyclone and
6. product collector.

- Microencapsulation by spray-drying is a low-cost commercial
process which is mostly used for the encapsulation of fragrances,
oils and flavors.
Steps:
1Core particles are dispersed in a polymer solution and sprayed into
a hot chamber.
2The shell material solidifies onto the core particles as the solvent
evaporates.
- The microcapsules obtained are of polynuclear or matrix type.

Spray congealing can be accomplished with spray drying
equipment when the protective coating is applied as a melt.
 Core material is dispersed in a coating material melt rather than
a coating solution.
 Coating solidification (and microencapsulation) is accomplished
by spraying the hot mixture into a cool air stream.
- e.g. microencapsulation of vitamins with digestible
waxes for taste masking.

Spray drying and congealing
52
Dispersing the core material in a
liquefied coating Substance /spraying
or introducing the coating mixture on
to core material.
Coating
drying is
solidification
effected
in spray
by rapid
evaporation of a solvent in which the
coating material is dissolved.
Coating solidification in spray
congealing method is accomplished
by thermally congealing a molten
coating material or by solidifying a
dissolved coating by introducing the
coating core material mixture into a
non-solvent.

Spray Drying
Spray Drying is the most commonly used encapsulation method in the
food industry.
The process is economical and flexible uses equipment that is readily
available, and produces particles of good quality.
The process involves three basic steps:
Preparation of a dispersion or emulsion to be processed
Homogenization of the dispersion and
Atomization of the mass into the drying chamber.
Spray dried ingredients typically have a very small particle size
(generally less than 100µm) which makes them highly soluble.
Typical shell materials include gum acacia, maltodextrins,
hydrophobically modified starch and mixtures. Other polysaccharides
like alginate, carboxymethylcellulose and guar gum.
Proteins like whey proteins, soy proteins, sodium caseinate can be used
as the wall material in spray drying.

SPRAY DRYING & CONGEALING ( COOLING)
Spray drying : spray = aqueous solution / Hotair
Spray congealing : spray = hot melt/cold air

Spray cooling/chilling is the least expensive encapsulation
technology.
It is used for the encapsulation of organic and inorganic salts,
textural ingredients, enzymes, flavors and other functional
ingredients.
It improves heat stability, delay release in wet environments,
and/or convert liquid hydrophilic ingredient into free flowing
powders.
Spray cooling/chilling is typically referred to as ‘matrix’
encapsulation because the particles are more adequately
described as aggregates of active ingredient particles buried in
the fat matrix.
Spray Cooling/ Chilling

MULTIORIFIC-CENTRIFUGAL PROCESS
The Southwest Research Institute (SWRI) has developed a
mechanical process for producing microcapsules that utilizes.
centrifugal forces to hurl a core material particle trough an
enveloping microencapsulation membrane thereby effecting
mechanical microencapsulation.
Processing variables include the rotational speed of the cylinder,
the flow rate of the core and coating materials, the concentration
and viscosity and surface tension of the core material.
The multiorifice-centrifugal process is capable for
microencapsulating liquids and solids of varied size ranges, with
diverse coating materials. The encapsulated product can be
supplied as slurry in the hardening media or as a dry powder.
Production rates of 50 to 75 pounds per our have been achieved
with the process.

PercentageYield
The total amount of microcapsules obtained was weighed and the
percentage yield calculated taking into consideration the weight of the
drug and polymer.
Percentage yield = Amount of microcapsule obtained / Theoretical
Amount×100
Scanning electron microscopy
•Scanning electron photomicrographs of drug loaded ethyl cellulose
microcapsules were taken. A small amount of microcapsules was spread
on gold stub and was placed in the scanning electron microscopy
(SEM) chamber.
•The SEM photomicrographs was taken at the acceleration voltage of
20 KV.
EVALUATION OF MICROCAPSULES

Particle size analysis
For size distribution analysis, different sizes in a batch were
separated by sieving by using a set of standard sieves. The
amounts retained on different sieves were weighed .
Encapsulation efficiency [8]
Encapsulation efficiency was calculated using the formula:
Encapsulation efficiency =
Actual Drug Content / Theoretical Drug Content ×100

Cefotaxime sodium drug content in the microcapsules was
calculated by UV spectrophotometric (Elico SL159 Mumbai India)
method.
The method was validated for linearity, accuracy and precision. A
sample of microcapsules equivalent to 100 mg was dissolved in 25
ml ethanol and the volume was adjusted upto 100 ml using
phosphate buffer of pH 7.4. The solution was filtered through
Whatman filter paper.
Then the filtrate was assayed for drug content by measuring the
absorbance at 254 nm after suitable dilution.
Estimation of Drug Content

Drug release was studied by using USP type II dissolution test apparatus
(Electrolab TDT 08L) in Phosphate buffer of pH 7.4 (900 ml). The paddle speed at
100 rpm and bath temperature at 37 ± 0.5°c were maintained through out the
experiment.
A sample of microcapsules equivalent to 100 mg of cefotaxime sodiumwas
used in each test. Aliquot equal to 5ml of dissolution medium was withdrawn at
specific time interval and replaced with fresh medium to maintain sink condition.
Sample was filtered through Whatman No. 1 filter paper and after suitable dilution
with medium; the absorbance was determined by UV spectrophotometer (Elico
SL159) at 254 nm.
All studies were conducted in triplicate (n=3). The release of drug from marketed
sustained release tablet was also studied to compare with release from
microcapsules.
Invitro Drug release Studies

APPLICATION OF MICROENCAPSULATION TECHNIQUES:

Applications of Microcapsules and Microspheres
1. AgriculturalApplications
 Reduce insect populations by disrupting their mating process.
 Protects the pheromone from oxidation and light during storage and
release.
2. Catalysis
 Safe handling, easy recovery, reuse and disposal at an acceptable
economic cost.
 Metal species such as palladium (II) acetate and osmium tetroxide
have been encapsulated in polyurea microcapsules and used
successfully as recoverable and reusable catalysts without
significant leaching and loss of activity.

3. Food Industry
 Adding ingredients to food products to improve nutritional value
can compromise their taste, colour, texture and aroma.
 Sometimes they slowly degrade and lose their activity, or become
hazardous by oxidation reactions.
 Ingredients can also react with components present in the food
system, which may limit bioavailability.
4. PharmaceuticalApplications
 Potential applications of this drug delivery system are
replacement of therapeutic agents (not taken orally today like
insulin), gene therapy and in use of vaccines for treating AIDS,
tumors, cancer and diabetes.
 The delivery of corrective gene sequences in the form of plasmid
DNA could provide convenient therapy for a number of genetic
diseases such as cystic fibrosis and hemophilia.

 Lupin has already launched in the market worlds first Cephalexin
(Ceff-ER) and Cefadroxil (Odoxil OD) antibiotic tablets for
treatment of bacterial infections.
 Aspirin controlled release version ZORprin CR tablets are used
for relieving arthritis symptoms.
 Quinidine gluconate CR tablets are used for treating and
preventing abnormal heart rhythms.
 Niaspan CR tablet is used for improving cholesterol levels and
thus reducing the risk for a heart attack.
 Some of the applications of microencapsulation can be
described in detail as given below:
1. Prolonged release dosage forms.
selectively2.Prepare enteric-coated dosage forms
absorbed in the intestine rather than the stomach.
3. It can be used to mask the taste of bitter drugs.
4. To reduce gastric irritation.

5. Used to aid in the addition of oily medicines to tableted dosage
forms.
To overcome problems inherent in producing tablets from otherwise
tacky granulations.
This was accomplished through improved flow properties.
eg. The non-flowable multicomponent solid mixture of niacin,
riboflavin, and thiamine hydrochloride and iron phosphate may be
encapsulated and made directly into tablets.
6.To protect drugs from environmental hazards such as humidity,
light, oxygen or heat. eg. vitamin A and K have been shown to be
protected from moisture and oxygen through microencapsulation.
7.The separations of incompatible substances, eg. pharmaceutical
eutectics.
The stability enhancement of incompatible aspirin-
accomplished bychlorpheniramine maleate mixture was
microencapsulating both of them before mixing.

67
Pharmaceutical Application
 To improve the flow properties. e.g. Thiamine, Riboflavine
 To enhance the stability. e.g. Vitamins
 To reduce the volatility of materials. e.g. Peppermint oil, Methyl
salicylate
 To avoid incompatibilities. e.g. Aspirin and Chloramphenicol
 To mask the unpeasant taste and odour. e.g. Aminophylline,
castor oil
 To convert liquids into solids. e.g. Castor oil, Eprazinone,
 To reduce gastric irritation. e.g. Nitrofurantoin, Indomethacin

 Microencapsulation has been employed to provide protection to the core
materials against atmospheric effects, e.g., Vitamin APalmitate.
 Separation of incompatible substance has been achieved by encapsulation
 To mask the bitter taste of drugs like Paracetamol, Nitrofurantoin etc.
 To reduce gastric and other gastro intestinal (G.I) tract irritations, For eg,
sustained release Aspirin preparations have been reported to cause
significantly less G.I. bleeding than conventional preparations
 A liquid can be converted to a pseudo-solid for easy handling and storage.
eg.Eprazinone.
 Hygroscopic properties of core materials may be reduced by
microencapsulation e.g. Sodium chloride.
 Carbon tetra chlorides and a number of other substances have been
microencapsulated to reduce their odour and volatility
 To reduce volatality of liquids like peppermint oil
 Helps to prepare SRDF and enteric coated products, controlled release
products
 Used to improve flow properties before compression into tablets 68

Brand name API Manufacturer
OROS CT
(osmotically
active tablets)
Colon specific drugs Alza corp.
ReGel
(oncogel
)
Paclitaxel Macro Med Inc.
Clopigrel clopidogrel+ Aspirin Lupin pinnacle
Clobitab clopidogrel+ Aspirin Lupin pinnacle
Atoplus Atorvastatin Triton (calyx)
69

70
 Jackson L. S.; Lee K. (1991-01-01). "Microencapsulation and the food
industry".Lebensmittle–WissenschaftTechnologie.
http://cat.inist.ft/?aModele=afficheN&cpsidt=5014466. Retrieved 1991-02-02.

Microencapsulation

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Microencapsulation