The technique in which the very small solid particles or liquid particles are coated with the polymer is called microencapsulation.
Even the macropacking can satisfy the demands which the microencapsules satisfy, but the main difference is the later is small in size.
* Controlled drug release is achieved.
* Liquids can be converted into solids that have free flowing properties.
* The drugs which are susceptible to oxidation,hydrolysis can be safeguarded.
* Microencapsulation can be used for those drugs which do not have pleasant taste and odor.
* Some of the drugs like peppermint oil are volatile and these can be safeguarded with the use of microencapsulation.
* If the drug is to be released in the intestine or some other desiredregion, it can be achieved with the aid of microencapsulation.
How the drug will
The following principles are involved in the drug release.
Degradation controlled monolithic system
Diffusion controlled monolithic system
Diffusion controlled reservoir system
Ideal properties of the coating Materials:
They should be inert
Should have no taste
Should have less viscosity and should not absorb water
METHODS USED IN THE MANUFACTURE:
There are two types of methods.
Physical methods and chemical methods.
AIR SUSPENSION COATING: In this process, the air is passed in the upward direction in which the particles to be coated are suspended. There is a plate which contains the small holes which gives support to the particles. The particles move upward in the stream of air and after sometime the speed decreases and the particles move to the outer bed and will come down. Then again they will move upwards and the process is repeated for several times.
COACERVATION:It includes the following steps
Dissolve shellac in water.
Add the material to microencapsulated to the above solution and it will get dispersed.
Lower the pH by adding acids like sulphuric acid or organic acids. This results in the separation of the shellac from solution and will surround the core material. (coacervation)
Now drying is done with use of spray drier or
fluidized bed drier.
PAN COATING: Here the material to be coated is introduced into the pan and then it is subjected to tumbling action. Then in the form of spray the coating is applied on to the particles. Generally the particles size must be greater than 600microns to achieve good coating. The excessive solvent is removed by keeping them in the tray drier or by passing
hot air over it.
SPRAY DRYING: In spray drying process, the particles to coated (core material) are suspended in the solution of the coating material. When the hot air is passed, the solvent absorbs the heat and will get evaporated and a film of coating material will be formed on the core material.
Solvent evaporation and polymerization are the methods involved in the process of Microencapsulation.
(accessed on 15th April 2011)
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