Extrusion-Spheronization is the traditional method for manufacturing pellets. Agglomeration through the extrusion and spheronization process has been used for many years. In fact, this process dates back to 1950’s when the first pelletized dosages were introduced to the market. These pelletized dosages gain popularity quickly due to their noticeable advantages. For example, it is easier to fill the capsule, enhance the drug dissolution, coat the pill, and control the delivery of ingested drug. These pills can be formed through a wide variety of techniques such as spray drying, spray congealing, hot-melt extrusion, and spheronization of low melting materials.
The figure above shows the classification of pelletization techniques. The extrusion-spheronization process is listed under compactation. Agitation is when the finely divided particles are transformed into spherical particles by balling. The appropriate quantity of liquid is added to the finely divided particles during a continuous rolling motion. Compactation is a form of pressure agglomeration where the particles are forced together or compressed in order to form pellets of the desired shape and size. The particles rearrange themselves to form a closely packed mass during compression. This means that during higher pressure, the particles are forces against each other. However, they are so tightly packed already. As a result, the particles are elongated and undergo elastic and plastic deformation. In the extrusion-spheronization process, the dry powder is first agglomerated with the aid of a binding liquid. Next, it is processed in the extruder to produce high density extrudates (material that has been extruded through a die). These extrudates are finally converted to pellets on spheronizer. Layering is the deposition of successful layers of drug particles from solution, suspension, or dry powder on the nuclei. There are 3 types of layering: powder, solution, and suspension layering. Out of the three, the suspension layering has been proven to be superior to the other two in terms of drug loading and enteric layering phase. Globulation is process where hot melt, solution, or suspension are atomized to generate spherical pellets. In the spray drying process, the atomized globules, or droplets, come in contact with a hot gas. This is when the droplets start to evaporate. Temperature, humidity, and transport properties of the air surrounding the droplet are all adjustable variables to form the ideal pellet. In the spray congealing, the temperature of the atomized droplets are lowered to below the melting point of the vehicles such as gums, wax, fatty acids, etc. A critical requirement in this process is that substances should have well-defined melting points or small melting zones.