The aim of this work is to study the influence of formulation parameters in the preparation of sustained release enzyme-loaded Eudragit S100 microspheres by emulsion solvent diffusion technique. A 32 full factorial experiment was designed to study the effects of the amount of solvent (dichloromethane) and stabilizers (Tween 20, 40, or 80) on the drug content and microsphere size. The results of analysis of variance test for both effects indicated that the test is significant. The effect of amount of stabilizer was found to be higher on both responses (SSY1=45.60; SSY2=737.93), whereas solvent concentration comparatively produced significant effect on the size of microspheres (SSY1=0.81; SSY2=358.83). Scanning electron microscopy of microspheres with maximum drug content (2.5 mL dichloromethane and 0.1 mL Tween 80) demonstrated smooth surface spherical particles with mean diameter of 56.83±2.88 µm. The effect of formulation variables on the integrity of enzyme was confirmed by in vitro proteolytic activity. The enteric nature of microspheres was evaluated and results demonstrated ~6% to 7% release of enzyme in acidic medium. The release of enzyme from microspheres followed Higuchi kinetics. In phosphate buffer, microspheres showed an initial burst release of 20.34%±2.35% in 1 hour with additional 58.79%±4.32% release in the next 5 hours. Three dimensional response graphs were presented to visualize the effect of independent variables on the chosen response. Thus, Eudragit S100 microspheres can be successfully prepared for oral delivery of enzymes with desirable characters in terms of maximum loading and diffusion release pattern.
Keywords: Enzyme delivery, factorial design, Tween 80, microspheres, 3D response graphs