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The present study was oriented towards microencapsulation of aspirin and the study of its release kinetics. The desired encapsulation was achieved by emulsion solvent evaporation method using ethyl cellulose (EC), cellulose acetate phthalate (CAP) and their mixture (1:1) of polymeric constituents. Characterization of the formulations was performed by size, shape, drug loading efficiency and in-vitro drug release analysis. The in-vitro release profiles from different polymeric microcapsules were applied on different kinetic models. The prepared microcapsules were found free flowing and almost spherical in shape with particle sizes ranging from 300-700μm, having a loading efficiency of 75- 85%. The best fit model with the highest correlation coefficient was observed in Higuchi model, indicating diffusion controlled principle. The n value obtained from Korsemeyer-Peppas model varied between 0.5-0.7, confirming that the mechanism of drug release was diffusion controlled. Comparative studies revealed that the release of aspirin from EC microcapsules was slower as compared to that of CAP and their binary mixture. [ABSTRACT FROM AUTHOR]

A study was carried out to investigate the solute permeability of various polymer films applied on aspirin crystal to form microcapsules. The coating materials were an acrylate methacrylate (AMA), poly 3‐hydroxybutyrate‐hydroxyvalerate (Biopol ® ) and poly (lactic‐glycolic) acid (PLGA). Organic solutions of the polymers were applied on the aspirin crystals (core) by a spray coating technique in a Wurster column. The microcapsule surfaces were investigated using scanning electron microscopy (SEM), while permeability studies were carried out on single microcapsules serving as micro dialysis cells. The amount of drug (m) permeating through the applied films in time (t) was analysed on the basis of Fickian diffusion. The SEM revealed numerous surface pores of size range 2.4 to 24 μm for the AMA films, while the PLGA and Biopol films, on the other hand, exhibited very few surface pores of size range 2.2 to 18 μm. However, the AMA films were more spongy than the PLGA and Biopol. The AMA films displayed a retarded release while the PLGA or Biopol films displayed a burst release, attributable to the differences in the film's porous structure. The Permeability coefficient (P) depended on the core weight of the single microcapsules, decreasing with increase in core weight. Thus, for an ensemble of the microcapsules the permeability coefficients of the films of the component microcapsules will have a distribution of P values even though the coating material is the same. This finding is important in the simulation of drug release from coated multiparticulate systems. [ABSTRACT FROM AUTHOR]