Effect of the cargo lipophilicity on powder micromeritics properties of drug-loaded solid lipid microparticles

Solid lipid microparticles (SLMs) have broad prospect as one of the lipid-based solid drug delivery system (LSDDS). Much attention should be paid to the powder micromeritic properties of SLMs for the strict requirement made by further development into solid preparation. However, the role of formulation factors in powder micromeritics properties still remains unknown. This study aims to evaluate the potential effect of drug lipophilicity on micromeritics properties of the lipophilic drug-loaded SLMs. Salicylic acid (SAA) and Diflunisal (DIF) were chosen as the model drugs for they have great difference on lipophilicity, and Stearic acid (SA) was selected as the model lipid. The two drug-loaded SLMs were investigated for their powder micromeritic and other properties for comparative study. The lipophilicity of drug exhibited difference in powder micromeritic properties of SLMs. SAA-SA had much lower encapsulation efficiency and drug loading with SAA mainly located on the outer layer when compared with DIF-SA, of which the more lipophilic DIF were encapsulated inside. Besides, SAA-SA also showed higher density and lower flowability, which is tended to aggregate. In summary, the SLMs loaded with more lipophilic drug would show better micromeritics properties. The different interparticle force caused by different drug distribution may explain the phenomenon.