Uniform ethyl cellulose microspheres of controlled sizes and polymer viscosities and their drug-release profiles

Monodisperse ethyl cellulose (EC) microspheres (MSs) of three size groups (20-35, 55-60, and 80-105 μm in diameter) were fabricated to study the effect of the MS size on the drug-release profiles with a novel scheme combining mechanical and hydrodynamic forces. More than 90% of the MSs were within ±3 μm of the average diameter, regardless of the EC viscosities used in the study. The effect of the polymer viscosity was also examined with ECs with two distinct viscosities (4 and 45 cp). The encapsulation efficiencies (EEs) of piroxicam and rhodamine were 6.4-51 and 63-80%, respectively. The drug distribution in the MSs showed a higher concentration near the particle surface, and this was more distinct with rhodamine. An approximately zero-order release was observed with the small MSs of 4-cp EC during 24 h without evident initial bursts. The MS size affected the surfacearea-to-volume ratio, EE, and intraparticle drug distribution, affecting the drug-release profiles.