Development and in vitro evaluation of topically applied cinnamic acid formulations

The aim of this study was to formulate microcapsulated cinnamic acid (CN) formulations in w/o and o/w emulsions and to compare their release profiles with w/o, o/w and w/o/w emulsions without microcapsules through cellulose acetate, cellulose nitrate membranes and excised rat skin. The experimental design approach was used for understanding the influence of different formulation factors on release characteristics and to optimise most accurate formulating parameters. The data obtained in this study were subjected to statistical analysis by a repeated measures ANOVA, following Bonferroni multiple comparisons test. A significantly different release was observed due to the core:wall ratio of microcapsules. Emulsions containing microcapsules with 2:1 core:wall ratio were found to be ideal according to the factorial design, dissolution and diffusion studies. The type of emulsion was found to be a very important factor affecting the release profile of CN. The results described in this study indicate that microencapsulation of CN in w/o emulsion could be suggested as an effective carrier for CN to achieve sustained release and to protect the drug. Moreover, w/o/w emulsions were also useful carriers for prolonged release by encapsulating the substances in their internal aqueous phase and they also protect drugs and their preparation and application are easy. By the way, in the case of o/w emulsion any significant difference was observed. The type of the membrane also affected release. According to the release results, rat skin was found to be significantly different from the synthetic membranes.