Granulation

Granulation
This technique is a variation of conventional wet granulation technique. It uses very little water to activate a binder and initiate agglomeration.18 This technique involves two steps, 1) wet agglomeration of the powder particles, and 2) moisture absorption or distribution. Agglomeration is facilitated by adding a small amount of water, usually less than 5% (1-4% preferably), to the mixture of drug, binder and other excipients. The two steps of this MADG are presented in Fig. 7. Agglomeration takes place when the granulating fluid (water) activates the binder. Once the agglomeration is achieved, moisture-absorbing material such as microcrystalline cellulose, silicon dioxide, etc. is added to facilitate the absorption of excess moisture. The moisture absorbents absorb the moisture from the agglomerates, resulting in moisture redistribution within the powder mixture, leading to relatively dry granule mixture. During this moisture redistribution process, some of the agglomerates remain intact in size without change, while some larger agglomerates may break leading to more uniform particle size distribution. It does not require an expensive drying step.19-21

In wet granulation, granules are formed by the addition of a granulation liquid onto a powder bed which is under the influence of an impeller (in a high-shear granulator), screws (in a twin screw granulator) [1] or air (in a fluidized bed granulator). The agitation resulting in the system along with the wetting of the components within the formulation results in the aggregation of the primary powder particles to produce wet granules.[1] The granulation liquid (fluid) contains a solvent or carrier material which must be volatile so that it can be removed by drying, and depending on the intended application, be non-toxic. Typical liquids include water, ethanol and isopropanol either alone or in combination. The liquid solution can be either aqueous based or solvent-based. Aqueous solutions have the advantage of being safer to deal with than other solvents.