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28 Pharmaceutical Technology ® Trends in Formulation eBook September 2024 PharmTech.com Pelletization coating process. Furthermore, variations in machine parameters such as spray rate, atomization pressure, dew point, and drying conditions may affect pellet quality. Additionally, environmental factors such as relative humidity and temperature can also impact coating integrit y. Therefore, precise control over these variables is essential to maintain consistent coating thickness and to enhance the overall quality of pellet formulation. Adhesion of coating material The adhesion of coating materials pertains to their ability to firmly adhere to the surface of pellets with- out experiencing peeling or f laking. This character- istic is pivotal for ensuring the efficacy, quality, and overall appearance of the product. During formu- lation specifically in coating and drying processes, the behavior of the polymer structure is crucial, in- f luencing adhesion, uniformity, and durability of coating. Polymer sticking at the surface is very much dependent upon the surface property of the core ma- terial. Irregularities on the surface may cause issues, such as sticking. The adhesion of coating material may be inf lu- enced by mechanical stress or handling during the coating process, such as tumbling in the coating pan or transfer between equipment. The same appropri- ate selection of the polymer is crucial. For instance, hydroxypropyl methylcellulose provides a f lexible coating t hat wit hstands stress and deformation, maintaining pellet integrity during handling and storage, while rigid coatings like ethyl cellulose may result in brittleness and cracking, compromis- ing overall formulation quality. So, the formulator should choose the polymer wisely while formulating. Sometimes the single polymer does not provide suf f icient ad hesion, necessitat ing t he use of du- al-polymer chemistr y. At this point the use of the mixture of two polymers yields better results. Ad- ditiona l ly, to increase t he f lex ibi lit y to t he poly- mer coat ing, it is adv isable to add plast icizer to strengthen the film property. The optimization of the material concentration and preparation method is therefore vital. Quality attributes of material The physiochemical properties of the material cho- sen for the pellet preparation plays a key role—im- pacting the overall performance of the product. It can affect the surface properties as well as the qual- ity. The surface properties of pellets are a critical fac- tor in pelletization, as coating integrity, the physical appearance, and patient acceptability rely on these. This is attributed to various factors including parti- cle size, particle size distributions, particle shapes, density, and surface area of the same. The properties of starting materials, including actives, polymers, and binders, have a significant inf luence on the surface roughness of pellets. It is evident that smaller par ticles result in smoother pellet surfaces due to better packing. For instance, MCC may yield smoother pellets compared to other excipients such as cross-povidone or lactose because of its ability to disaggregate into smaller particles during wetting. The hydrophilicity and hydrophobicity of the ac- tive ingredients play significant roles in pellet for- mulation. A powder containing hydrophobic drugs can pose challenges during extrusion and spheroni- zation due to limited wettability. Whereas the pellet containing the hydrophobic drug can pose a chal- lenge due to its higher wettability. Hence, the selec- tion of the solvents and the technique also depends upon the solubility and quantity of active material. There exist few moisture-sensitive actives that can pose challenges during pelletization. To address these challenges, materials like glyceryl monostea- rate (GMS) can be utilized. GMS effectively reduces water content i n t he for mu l at ion , res u lt i ng i n smoother surfaces and reduced porosity in the pel- lets. By minimizing moisture content, GMS facil- itates better pellet formation—enhancing overall product appearance. Moisture content of the wet mass The moisture content of the wet mass significantly inf luences the size, shape, and strength of pellets produced during extrusion. Pellet size increases with higher moisture content. Excessive moisture in the wet mass tends to increase cohesiveness among the powder particles, leading to the formation of agglom- erates. Conversely, low moisture content can result in the generation of fines (powder particles) during pelletization due to reduced plasticity of the liquid phase, which prevents proper adhesion of powder particles to the core bead. It is important to optimize the drying process to stabilize the prepared pellets. Uniform coating is crucial in pellet development, especially for maintaining the integrity of the coating process and achieving the desired drug release pattern, which—in turn—guarantees pellet quality.