Microencapsulation involves coating small particles or droplets to form microcapsules. It can be used to modify drug release timing and mask tastes. Various coating materials can be used depending on the product requirements. Common microencapsulation methods include spray drying, fluidized bed coating, pan coating, coacervation, and solvent evaporation. These methods use different processes but generally involve applying a coating and hardening it to form microcapsules encapsulating core materials. Microencapsulation offers various applications in pharmaceutical products.

1. Microencapsulation
As a process, it is a means of applying
relatively thin coatings to small particles
of solids or droplets of liquids and
dispersions.
The uniqueness microencapsulation is
of smallness of the coated particles and
their subsequent adaptation to a wide
variety of dosage forms and product
application.

2. Applications
The applications of microencapsulation
well includes in the formulation of
 Sustain release medications
 Delayed release medications
 Taste masked chewable tablets
 Single layer tablet containing
incompatible ingredients.

3. Coating material
The selection of a specific coating
material from a lengthy list of
candidate material presents the
following questions to be considered
by the research pharmacist.
 What is the specific dosage or product
requirement e.g. stabilization, reduced
volatility or release characteristics etc.

4. Cont…..
 What coating material will satisfy the
product objective and requirement.
 What microencapsulation method is
best suited to accomplish the coated
product objective?

5. Cont…..
 In-addition the coating material
should be capable of forming a
film that is cohesive with the core
material, be chemically compatible
and non reactive with the core
material and provide desired
coating properties such as
stability.

6. A typical coating materials commonly used in the
various microencapsulation method is as follows
 Water soluble polymers : - gelatin, starch,
polyvinyl pyrolidone, carboxy methyl cellulose,
methyl cellulose, hydroxyethylcellulose,
polyvinylacetate.
 Water insoluble polymers :- ethylcellulose,
polyethylene, polymethacrylate, cellulose nitrate.
 Waxes and lipids :- bees wax, carnauba wax,
spermaceti.
 Enteric resin s : - shellac, cellulose acetate
phathalate, zein, HPMC phathalate, Eudragit L&S,
polyvinyl acetate phathate.

7. Methodology
Microencapsulation methods that have
been or are being adapted to
pharmaceutical use include
 Air suspension also known as fluidized
bed coating.
 Spray drying
 Pan coating
 Coacervation- phase separation
 Solvent evaporation.

8. Microencapsulation process Applicable
 Air suspension- Solids-35-5000 or more
( Size in micron)
 Spray drying- Solids and liquids-600
 Pan Coating- Solids- 600-5000 or more
 Coacervation–Phase separation- Solids
and liquids-2-5000 or more
 Solvent Evaporation- Solids and liquids-
2-5000 or more

9. Air suspension or fluidized bed coating
 it is also known as wurster process ,
consist of the dispersing of solid particulate
core material in a coating chamber. The
particles are suspending on an upward
moving hot air stream (fluidization) and
coating material usually a polymer solution
is applied in the form of spray to the moving
particles. The supporting air stream also
serves to dry the product while it is being
encapsulated.

10. FLUID BED DRYER

11. Process variables that receive
consideration for efficient
encapsulation includes
 Melting point, solubility, friability,
volatility of the core material.
 Coating material concentration.
 Nature of the vehicle
 Coating material application rate
 Air velocity for fluidization.
 Inlet air temperature.

12. Spray drying
 In practice, microencapsulation by spray
drying is conducted by dispersing the core
material in a coating solution, in which the
coating polymer is dissolved and the core
material is insoluble and then atomizing the
mixture in to an air stream. The air is
usually heated required to remove the
solvent from the coating material thus
forming a microencapsulated product.

13. SPRAY DRYER
 The equipment components of a
standard spray drier include
 an air heater
 atomizer
 spray chamber
 blower and
 product collector.

14. SPRAY DRYER

15. Process variables
includes
 Concentration of coating material.
 Nature of the vehicle.
 Concentration of the core.
 Feed rate.
 Inlet air temperature.

16. Pan coating
 The microencapsulation of relatively
large particles greater than 600
microns in size by pan methods has
become widespread in the
pharmaceutical industry.
 The method involves the application of
a coating composition to a moving bed
of particles with the concurrent use of
heated air to facilitate evaporation of
the solvent.

17. STANDARD COATING PAN
 The standard coating pan consist of
a circular metal pan usually stainless
steel of 8 o 60 inch in diameter
mounted on a stand and rotates on
its horizontal axis by a motor. The
coating solutions are applied by
spraying the material on the rotating
particulate bed.

18. STANDARD COATING PAN

19. Process variables includes
 Diameter and speed of rotation of
the coating pan.
 In let air temperature.
 Concentration of coating material.
 Nature of the vehicle used for the
preparation of coating solution.
 Spray rate.

20. Coacervation- Phase Separation
Microencapsulation by coacervation phase
separation processes consist of three
steps carried out under continues
agitation.
 Formation of three immiscible chemical
phases
 Deposition of the coating
 Rigidization of the coating.

21. Step I
 Step I of the process is the formation
of three immiscible chemical phases, a
liquid manufacturing vehicle phase.
Core material phase and a coating
material phase.
 To form three phases, the core material
is dispersed in a solution of the coating
polymer, the solvent for the polymer
being the liquid manufacturing vehicle
phase.

22. Cont…
 The coating material phase, an
immiscible polymer in a liquid phase is
formed by utilization of one of the
method s of phase separation
coacervation i.e. by changing the
temperature of the polymer solution, or
by adding the salt, non solvent, or
incompatible polymer.

23. Step II
 Step II of the process consists of depositing
the liquid polymer coating upon the core
material. this is one by controlled physical
mixing of the coating material while in liquid
and the core material in the manufacturing
vehicle. Deposition of the liquid polymer
coating around the core material occurs if the
polymer is adsorbed at the interface between
the core material and the liquid vehicle
phase.

24. Step III
 Step III of the process involves
rigidizating the coating.

25. FLOW DIAGRAM

26. Coacervation-phase separation by
Temperature change( Phase Diagram)

27. Explanation
 Figure illustrates a general
temperature- composition phase
diagram for a binary system comprised
of a polymer and a solvent. A system
having an overall composition
represented as point X , exist as a
single phase, homogeneous solution
at all points above the phase boundary
i.e. FEG .

28. Cont….
 As the temperature of the system decreased
from point A along the arrowed line AEB ,
the phase boundary is crossed at point E ,
and the two phase region is entered.

29. Cont…
 The phase separation of the dissolved
polymer occurs in the form of liquid
droplets and if the core material is
present in the system, under proper
polymer concentration and
temperature, and agitation conditions,
the liquid polymer droplets deposit
around the core particles thus forming
microcapsules.

30. Cont…..
 The phase boundary curve indicates that the
decreasing temperature, one phase
becomes polymer poor (vehicle phase) and
the second phase (coating material phase)
becomes polymer rich. At point B the vehicle
phase is pure solvent, at C coexisting phase
and at D, concentrated polymer-solvent
mixture.

31. The example illustrates the microencapsulation by temperature
change.
 Ethyl cellulose is insoluble in cyclohexane at room
temperature but is soluble at elevated temperature.
Thus 2% solution of ethyl cellulose is prepared in
cyclohexane by heating to the boiling point. The
core material n-acetyl para amino phenol is
dispersed in the solution with stirring in the ratio of
1:2( coat: core). Allow the mixture to cool with
constant stirring, effects phase separation of ethyl
cellulose and microencapsulation of the core
material. Further cooling results in the solidification
of the coating. The microencapsulated product is
then collected by filtration or centrifugation.

32. Coacervation-phase separation by Incompatible polymer
addition
Phase Diagram

33. Cont…..
 The diagram illustrates a ternary system
consisting of a solvent, and two polymers X
and Y. if an insoluble core material is
dispersed in a solution of polymer Y(at point
A in the figure) and polymer X( incompatible
polymer) is added to the system denoted by
the arrow line, the phase boundary is
crossed at point E. further addition of
polymer X, liquid polymer i.e polymer Y will
separated out as droplets and coating of
microcapsules exist at point B.

34. Example
 Microencapsulation of methylene blue
HCL with ethyl cellulose by this mode
is described as follows:- Ethyl cellulose
dissolve in toluene to yield polymer
concentration of 2% by weight. The
methylene blue HCL, being insoluble in
toluene, is dispersed with stirring in a
polymer solution at a ratio of 4 parts of
methylene blue HCL to 1 pqrt of
ethylcellulose.

35. Cont…
 Phase separation is done by slowly adding
liquid polybutadiene. The polybutadiene
being quite soluble in toluene and
incompatible with ethylcellulose effects the
separation of ethylcellulose from the
polybutadiene toluene solution and
subsequent microencapsulation of the
dispersed core material. The
microencapsulated product is then collected
by filtration or centrifugation.

36. Solvent evaporation
 The microcapsule coating is dissolved in a
volatile solvent which is immiscible with the liquid
manufacturing vehicle phase. A core material to
be microencapsulated is dispersed in the coating
polymer solution with agitation. The mixture is
then heated to evaporate the solvent for the
polymer with continues agitation. Once all the
solvent for the polymer is evaporated, the liquid
temperature is reduce to ambient temperature.
The microencapsulated product is then collected
by filtration or centrifugation.

37. Process variables
– Temperature for evaporation of
polymer solvent
– Agitation rate.