Solution and Suspension Coating, and Solvent Coating

By: Gary Wada on May 12, 2015

In Microencapsulation part 1, I discussed “hot melt encapsulation”. It is a very efficient process because the coating is applied at 100% solids as it is molten. Today’s blog, we will consider solution and suspension coating, and solvent coating.

Microencapsution with a water soluble coating material can be done using top spray fluid bed coating methods. You might want to microencapsulate a hydroscopic ingredient, but not affect its release characteristic greatly. By encapsulating) or agglomerating) with a water soluble material, we can reduce the substrate’s hydroscopicity, while not greatly impacting its release rate. Film coated tablets are an example of applying a water soluble coating to change the surface of an ingredient to mask its flavor, until it is swallowed. Then the coating dissolves quickly and the tablet ingredients are released. We can provide the same type of coating onto powders, crystals, and granules. Sometimes an ingredient is coated to change the color or appearance, to make it shinier for example.

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Suspension Layering

A form of encapsulation can be done by using a technique called fluid bed suspension layering. This could be performed when you have an water insoluble active that needs a reproducible controlled release profile. In this case, it might be wise to suspension layer the active onto an inert sphere, like a non-pareil. This should be a highly reproducible process, yield beads in a very narrow particle size range. These can then be coated with a sustained release coating to give the functional release profile desired. 

Solvent Coating

Solvent coating is another fluid bed process used to apply a water insoluble coating (such as ethylcellulose dissolved in alcohol) onto a substrate. This might be used where the substrate is incompatible with water, or extremely fine. Where the hot melt encapsulation was economical because it was applied at 100 % solids, solvent coating in comparison can be looked at as expensive, because of the cost of the solvent.

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We have alot of other information available on the Microencapsulation page of our website.