Tuning the formation and stability of microcapsules by environmental conditions and chitosan structure.

The goal of this work is to tune the formation and stability of the alginate-chitosan (AC) polyelectrolyte complexes (PECs) and microcapsules. Particularly, we explore the role of the conformation of chitosan on its interaction with alginate to understand the mechanism underpinning their interactions at the molecular level. Reducing the charge density by increasing pH will increase the compactness of chitosan, the values of the enthalpy (H) and stoichiometry (N) of binding between chitosan and alginate. Consequently, chitosan has advantage in being adsorbed on alginate beads to form microcapsules, including the binding rate and binding amount. Though the total heat release remain similar in the range of ionic strength, chitosan diffuses much easier into alginate hydrogels when in higher ionic strength. Increasing pH and ionic strength both help AC microcapsules to have higher stability. The results indicate that the formation and stability of AC microcapsules are related to the rigidity and conformations of chitosan molecules. After increasing acetylation degree (DA) of chitosan, the binding rate of chitosan and mechanical strength of AC microcapsules are both reduced. This work demonstrates the versatility and feasibility of tuning the formation and stability of polysaccharide microcapsules by physical factors and chitosan chemical structures.