Wet granulation and mixing

Granulation is a size enlargement process in which mixtures of fine powders are combined into larger agglomerates or granules. In wet granulation, a liquid and a binder material are added to an agitated powder bed to form granules. Common types of wet granulation equipment used in the pharmaceutical industry include mixer granulators where the powder is agitated by a large impeller at the base of mixer bowl, or fluid bed granulators where air is blown upwards through the powder to agitate and fluidize the particles. Drying of the granules drives off the liquid but a network of solid bridges and polymeric chains give strength and cohesion to the new granules. A simple method to analyse the extent of blending and mixing of drug after wet granulation is to conduct a 'sieve fraction assay', where the granules are sieved into size fractions and each size fraction is assayed for drug content.