Biodegradable microcapsules prepared by a w/o/w technique: Effects of shear force to make a primary w/o emulsion on their morphology and protein release

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Abstract
A water-in-oil-in-water (w/o/w) technique, sometimes known as in-water drying method, was used to prepare microcapsules consisting of polylactic acid and poly(lactide-co-glycolide). The influence of shear force to produce an initial water-in-oil (w/o) emulsion on the characteristics of microcapsules and protein release was investigated. Bovine serum albumin (BSA) was used as the model protein drug for encapsulation. The initial w/o emulsion was prepared by a Polytron homogenizer. The shear rate was varied from 11 to 23 krpm to produce w/o emulsions with different shear forces. This study revealed pronounced effects of shear force on the characteristics of microcapsules and release profiles of BSA. Depending on the degree of the shear applied, the inner structure of microcapsules showed very different morphology, which was responsible for different release patterns. A low shear produced microcapsules with a high initial burst release of BSA, whereas microcapsules using a high shear exhibited a controlled release of protein without any initial burst release. Also, at a given shear force, a variation in polymer composition of microcapsules was found to be effective in controlling the release characteristics of protein. Thus, the homogenization technique should be carefully considered in designing microcapsules with desirable release profiles of proteins and an adequate period of protein delivery.

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