Preparation and characterization of sodium alginate/chitosan microparticles containing esculin

Abstract

In this work, naturally occurring esculin (6,7-dihydroxycoumarin-6-glucoside), of great potential in therapy of nephrolithiasis − was successfully encapsulated in sodium alginate/chitosan hydrogel matrix by means of extrusion/external gelation-based and emulsification/internal gelation-based methods and the final microparticles were characterized with regard to structure and morphology, particle size and its distribution, swelling and release kinetics. Considering the fact, that the selected bioactive compound may be partially degradable in the aggressive conditions of the upper gastrointestinal tract, it was essential to develop a suitable carrier in order to provide its functional release directly in the small intestine. Therefore, in vitro release profiles of the microparticles were also investigated in order to provide the most effective encapsulation procedures in terms of operating conditions coupled with functionality of the fabricated particles, especially their ability to encapsulate the studied cargo, protect it under the simulated gastric conditions and promote its release under intestinal ones. The observed distinctions between the results of extensively physico-chemical studies obtained for both types of microparticles were the result of different matrix structures. The esculin cargo was successfully encapsulated with relatively high efficacies into both types of alginate/chitosan particles (ACPs). However, products prepared with an internal gelation/emulsification-based method remained more stable in different media and revealed the desired pH-dependent cargo release ability in vitro. The ACPs protected esculin in the simulated upper gastrointestinal tract, and enabled its release under the simulated intestinal conditions. The hydrogel microparticles thus obtained may be contributed as an effective delivery system for other therapeutic phenolic compounds, when it is necessary to maintain their stability during passage through the upper gastrointestinal tract to deliver them directly to the intestine.