Cross-linking mechanisms of calcium and zinc in production of alginate microspheres.

Calcium chloride and zinc sulphate were used to cross-link alginate microspheres prepared by an emulsification method. The microspheres cross-linked by a combination of these two salts showed different morphology and slower drug release compared with those cross-linked by the calcium salt alone. From viscosity study, it was found that zinc cations interacted with the alginate molecules to a greater extent than calcium cations. The varying effects of the salts on the properties of the microspheres were largely attributed to their ability to interact with the alginate molecules.