EFFECT OF IONOTROPIC GELATION AND ELECTROSTATIC COMPLEXATION ON THE MODULATION OF THE PROPERTIES OF SODIUM ALGINATE-CHITOSAN HYDROGELS

Alginate and chitosan are biopolymers widely explored for the delivery of bioactives, while alginate offers protection at acidic pH, chitosan provides mucoadhesiveness and a controlled release of target compounds at alkaline pH. However, the delivery properties of these systems can still be improved by controlling the interaction and gelation process of the biopolymer network, specially concerning the delivery of small molecules. This work aimed to evaluate how different techniques of formation and coating of alginate particles by chitosan affect their mechanical, chemical, structural, and delivery properties of cyanocobalamin (Vitamin B12). The effect of pH on the polymer network was evaluated in alginate microspheres prepared by alginate dripping in calcium chloride at different pH values (2.5 and 6.0). The interaction with chitosan was induced in two different ways: i) in a single step, adding chitosan in the crosslinking bath, or ii) in two steps, covering the microspheres previously formed by the subsequent immersion in chitosan solution. The zeta potential results confirmed that in all processes, the electrostatic interaction between alginate and chitosan was favored, i.e., alginate was negatively charged, and chitosan presented positive charges. The particles without chitosan presented large pores, which resulted in low mechanical strength and less vitamin retention. Conversely, extruded particles at pH 6.0 were more stable regarding the mass variation overtime at pH 2.5, 3.5, or 4.5. Indeed, the presence of an external layer of chitosan and smaller pores changed the stability and delivery properties of the particles. The sample produced in one step showed high retention of bioactive (39.73% of vitamin B12) than the non-coated ones and prepared in two steps. Despite traditional alginate–chitosan systems being usually prepared in two steps, our results confirm the feasibility of simplifying the particle formation in addition to enhance the retention of vitamin B12. The one-step production of alginate-chitosan particles proved to be a promising technique for the transport and delivery of bioactives.