An introduction to microencapsulation
- It is the process of applying relatively thin coatings to tiny particles of solids or droplets of liquids or dispersion(1).
- Microencapsulation involves coating of particles ranging from several tenth of micron to 5000 microns in size(1).
what is microencapsulation???
It is the process in which small particles or droplets are surrounded by a coating to give small capsules .it has many useful properties. In a relatively simplistic form, a microcapsule is a small sphere with uniform wall around it. The material inside microcapsule is referred to as the core, internal phase, or fill, whereas the wall is sometimes called a shell or coating or membrane. Most microcapsules have diameters between a few micrometers - few millimeters(2).
reasons for microencapsulation???
The reasons for the microencapsulation are countless.
* In some of the cases, the core must be isolated from its surroundings, as in isolating vitamins from the deteriorating effects of oxygen, retarding evaporation of volatile core, improving the handling properties of sticky material, or isolating a reactive core from a chemical attack(2).
* In some other cases, the objective is not to isolate the core completely but to control the rate at which it leaves the microcapsule, as in controlled release of drugs or pesticides.
* The problem may be as simple as masking the taste or odour of the core, or as complex as increasing the selectivity of an extraction or adsorption process.
purpose of microencapsulation???
* It provides the means to convert liquids to solids, of altering colloidal & surface properties.
* Provide environmental protection.
* Use for controlling the release characteristics. Because of the smallness of particles, drug moieties can be widely distributed throughout the gastrointestinal tract, thus potentially improving the drug absorption(3).
Applications of microencapsulation
Microencapsulation technique employed for production of:
- Sustained release or prolonged action of medications.
- Taste masked chewable tablets, suspensions and powders
- Stabilization to oxidation process.
- Reduction of the volatility.
- Conversion of liquid to solid
- Reduced gastric irritation.
- Also a new formulation concept for creams, ointments, aerosols, and suppositories(4)
Microencapsulation process involves basic understanding of the general properties of microcapsules such as nature of core & coating materials, the stability & release characteristics of the coated materials and microencapsulation methods(4).
techniques of microencapsulation
1. Air Suspension Process
2. Coacervation - Phase Separation Process
3. Pan Coating process
4. Solvent Evaporation process
5. Spray Drying and Spray Congealing
6. Interfacial Polymerization
7. Multi orifice Centrifugal Process(4)
Air suspension process
- it is also known as wurster process.
- this Process consists of dispersion of solid, particulate core materials in a supporting air stream and the spray coating of the air suspended particles.
- Within the coating chamber, particles are suspended in an upward moving air stream. Particles are recirculated through the coating zone portion of the chamber, where coating material, usually a polymer solution and it is sprayed to the moving particles.
- During each pass through coating zone, the core material receives an increment of coating material.
- The cyclic process is repeated several hundred times during processing, depending on the purpose of microencapsulation and the coating thickness that is desired(4).
- This process is applicable only for encapsulation of solid core material.
-the Particle size ranges from 35- 5000u.
Coacervation - Phase Sepration Process
This process comprises of three steps:
a. Formation of three immiscible chemical phases.
b. Deposition of the coating.
c. Rigidization of the coating.
b. Deposition of the coating.
c. Rigidization of the coating.
Step I: Formation of three immiscible chemical phases
(i) a liquid manufacturing vehicle phase
(ii) a core material phase and
(iii) a coating material phase.
To form the three phases, initially a core material is dispersed in a solution of the coating polymer. The solvent for a polymer being the liquid manufacturing vehicle phase. The coating material phase, an immiscible polymer is in a liquid state, is formed by utilizing one of the methods of phase separation coacervation, that is:
* By changing the temperature of polymer solution.
* By adding a salt By adding a non-solvent
* By adding incompatible polymer to the polymer solution
* By inducing a polymer-polymer interaction.
Step II: Deposition of the coating:
This process consists of the deposition of the liquid polymer coating upon the core material. This is accomplished by controlled physical mixing of coating material and the core material in manufacturing vehicle.
Deposition of the liquid polymer coating around the core material occurs if the polymer is adsorbed at the interface formed between the core material and liquid vehicle phase. This adsorption phenomenon results in an effective coating(4).
Step III: Rigidization of the coating:
Rigidization of coating is done by cross- linking, thermal, or desolvation techniques to form self sustaining microcapsules.
- coacervation -it is a phase separation process applicable for solids and liquids.
- the Particle size ranges from 2- 5000 u.
methods for phase separation coacervation
i) Temperature Change -It involves a change in the temperature, which results in the separation of phases. With decrease in the temperature, one phase becomes polymer poor (microencapsulation vehicle phase) and second phase (coating material phase) becomes polymer rich. Phase separation of dissolved polymer occur in the form of immiscible droplets.
Under proper concentration of the polymer, temperature and agitation condition, liquid polymer droplets coalesce around the dispersed core material particle, and results in the formation of embryonic microcapsule.
ii) Incompatible Polymer Addition - Liquid phase separation of the polymeric coating material and microencapsulation can be accomplished by utilizing an incompatibility of dissimilar polymer existing in the common solvent.
iii) Non- Solvent Addition - This method involves addition of a liquid that is a non solvent for given polymer to a solution of polymer, to induce phase separation(4).
iv) Salt Addition - It involves addition of soluble inorganic salts to aqueous solution of certain water soluble polymers to cause the phase separation process.
v) Polymer - Polymer Interaction- It involves interaction of oppositely charged polyelectrolytes, which results in the formation of a complex having such reduced solubility that causes the phase separation.
1.http://www.pharmpedia.com/Main_page(accessed on feb14th 20:26)
2.http://serendip.brynmawr.edu/exchange/node%20/%E2%80%9Dhttp%3A/%252Fwww....(accessed on feb14th 20:26)
3.http://members.fortunecity.com/micrometrix/(accessed on feb14th 20:26)
4.http://www.pharmpedia.com/Main_page(accessed on feb14th 20:26)
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to be continued in my next blog....