Solid Dosage Forms

TIU

FACULTY OF PHARMACY

PHARMACEUTICAL TECHNOLOGY III

2020-2021

Lec. Dr. Muath Sheet Mohammed Ameen Lec. 7

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 100μ in size.

Microcapsule can be dividing into two parts, namely the

core and the shell (Figure 5)

Figure 5: Mononuclear Microcapsules

Core

(Active ingredient, Drug)

Shell (Polymer, Coating / encapsulation material)

Reasons For Microencapsulation1. To protect reactive substances from the environment.

2. To convert liquid active components into a dry solid system

3. Isolation of core from its surroundings, as in isolating vitamins

from the deteriorating effects of oxygen

4. Isolating a reactive core from chemical attack

5. For safe handling of the toxic materials

6. To get targeted release of the drug

7. To control release of the active components

8. To masking the taste or odor of the core

9. To increase of bioavailability

10. Protects the GIT from irritant effects of the drug

Pharmaceutical ApplicationTo 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 unpleasat taste and odor (e.g. Aminophylline, Castor oil)

To convert liquids into pseudo-solids for easy handling and storage (e.g. Castor

oil, Eprazinone).

To reduce gastric irritation (e.g. Nitrofurantoin, Indomethacin).

To reduce hygroscopic properties of core materials (e.g. Sodium Chloride)

Formulation of Microencapsulation

Generally microencapsulations 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.

It may be liquid or solid or gas.

b. Shell material

It is compatible, nonreactive with core material.

Provide desired coating properties like strength, flexibility,

impermeability, optical properties, non hygroscopicity, tasteless

and stable.

It is inert substance which coats on core with desired thickness.

Formulation of Microencapsulation

Compositions of coating are

Inert polymer

Plasticizer

Coloring agent

Resins, waxes and lipids

Release rate enhancers or retardants.

Polymers are used widely in pharmaceutical systems as adjuvants,

coating materials and, a components of controlled and site-specific

drug delivery systems

Formulation of Microencapsulation

List of Coating MaterialsWater soluble

resinsWater insoluble

resinsWaxes & lipids Enteric resins

Gelatin Ethyl cellulose Paraffin Shellac

Gum arabic Polyethylene Carnuba wax Zein

PVP Polymethacrylate Bees wax CAP

CMC Cellulose nitrate Stearic acid

Methyl cellulose Silicones Stearyl alcohol

Arabinogalactan

Polyvinyl acrylate

Polyacrylic acid

Formulation of Microencapsulation

Properties of Some Microencapsulation Core Materials

Core MaterialCharacteristic

PropertyPurposes of Encapsulation

Final Product

Form

AspirinSlightly water

soluble solid

Taste-masking;

sustained release;

reduced gastric irritation;

separation of incompatibiles

Tablet or

Capsule

Vitamin A PalmitateNonvolatile

liquidStabilization to oxidation Dry powder

Isosorbide dinitrateWater soluble

solidSustained release Capsule

Menthol/methyl

Salicylate camphor

mixture

Volatile

Solution

Reduction of Volatility;

Sustained Release.Lotion

Release MechanismsA 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 enzymatic attack.

By chemical reaction.

By hydrolysis or slow disintegration.

Microencapsulation Techniques1. 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 antisolvent method (SAS)

11. Nozzel vibration technology

CoacervationIt 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.

It also means formation of three immiscible phases of core

material, solvent (liquid manufacture vehicle phase) and coating

material. Deposition of the coating material on the core.

Rigidisation of coating to form self-sustained microencapsules

Coacervation is typically used to encapsulate flavor oil.

It can also be adapted for the encapsulation of fish oils, nutrients,

vitamins, preservatives and enzymes.

CoacervationCoating material phase formed by utilizing following methods:

a. Temperature & pH change

b. Addition of incompatible polymer

c. Addition of nonsolvent

d. Addition of salt

e. Polymer –polymer interaction

Solvent Evaporation

In the case in which the core material is dispersed in the polymer

solution, polymer shrinks around the core (Figure 6).

In the case in which core material is dissolved in the coating

polymer solution, a matrix-type microcapsule is formed (Figure 6).

The process is precipitating small polymer particles from an oil - in

water emulsion (Figure 7).

The core materials may be either water soluble or water insoluble.

A variety of film – forming polymers can be used as coatings.

Example: Poly-styrene coated diltiazem resin complex

Figure 6: Solvent Evaporation Process

Figure 7: Solvent Evaporation Process

Evaluation of Microencapsules

1. Percentage Yield

2. Scanning Electron Microscopy (SEM)

3. Particle Size Analysis

4. Encapsulation Efficacy

5. Estimation of Drug Content

6. Invitro Drug Release Studies

Percentage Yield

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 x 100

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

Encapsulation efficiency was calculated using the formula:

Encapsulation efficiency=Actual Drug Content/ Theoretical Drug Content x 100