title: Formation of alginate microspheres produced using emulsification technique.
abstract: This study investigated the formative process of alginate microspheres produced using an emulsification technique. The alginate microspheres were produced by cross-linking alginate globules dispersed in a continuous organic phase using various calcium salts: calcium chloride, calcium acetate, calcium lactate and calcium gluconate. The size, shape, drug content and Ca2+ content of the microspheres were evaluated. The tack, viscosity and pH of the calcium salt solution and percentage of Ca2+ partitioned into the organic phase were determined. Microscopic examination of the test emulsion at various stages of the emulsification process was also carried out. The propensity of cross-linking reaction was found to be dependent on successful collision between alginate and calcium salt globules. Examination of the characteristics of microspheres indicated that the formed microsphere was a resultant product of alginate globule clustering. The growth propensity of microspheres was promoted by the higher rate and extent of cross-linkage which was governed by the pH, tack and/or Ca2+ content of the cross-linking solution, as well as the dissociation constant and diffusivity of the calcium salt. Overall, the amount of free Ca2+ cross-linked with alginate in the formed microspheres was in the following order: calcium acetate > calcium chloride + calcium acetate > calcium chloride + calcium gluconate; calcium chloride + calcium lactate > calcium chloride. In microencapsulation by emulsification, the mean size of the microspheres produced can be modified by varying the tack, pH and Ca2+ content of the cross-linking solution and through the use of a combination of calcium salts. The shape of the microspheres produced was, nonetheless, unaffected by the physicochemical properties of the cross-linking solution.
authors.affiliation: Department of Pharmacy, Faculty of Science, National University of Singapore, 18 Science Drive 4, Singapore 117543. phapaulh@nus.edu.sg
authors.forename: P W S
authors.initials: PW
authors.lastname: Heng
authors.forename: L W
authors.initials: LW
authors.lastname: Chan
authors.forename: T W
authors.initials: TW
authors.lastname: Wong
mesh_terms: D000464:Alginates / Q000737:chemistry*; D002118:Calcium / Q000737:chemistry; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D003432:Cross-Linking Reagents / Q000737:chemistry; D004337:Drug Carriers / Q000737:chemistry; D004339:Drug Compounding / Q000379:methods*; D004655:Emulsions / Q000737:chemistry; D020723:Glucuronic Acid; D006603:Hexuronic Acids; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008863:Microspheres; D010316:Particle Size; D014783:Viscosity
chemical_list: D000464:Alginates; D003432:Cross-Linking Reagents; D004337:Drug Carriers; D004655:Emulsions; D006603:Hexuronic Acids; D020723:Glucuronic Acid; D002118:Calcium