title: The dramatic effect of small pH changes on the properties of chitosan hydrogels crosslinked with genipin.
abstract: We report on intriguing new phenomena related to the creation of chitosan hydrogels crosslinked with genipin. We found that the reaction between chitosan and genipin is very slow, sometimes requiring more than four days until completed. Further, we discovered that altering the pH within the small range of 4.00-5.50 dramatically affects the reaction, leading to hydrogels differing both in appearance and in properties. Increasing the pH by 1.5 units led to an almost fourfold decrease in the gelation time and more than tenfold equilibrium swelling. A correlation between the percentage of unreacted genipin molecules and the hydrogel properties was identified. The strong pH dependency was attributed to the degree of chitosan protonation and to the inability of protonated chitosan to react with genipin. This research shows, for the first time, that minor changes in the pH can lead to substantially different hydrogels.
authors.affiliation: The Russell Berrie Nanotechnology Institute, Technion - Israel Institute of Technology, Haifa 32000, Israel.
authors.forename: Keren
authors.initials: K
authors.lastname: Delmar
authors.affiliation: The Russell Berrie Nanotechnology Institute, Technion - Israel Institute of Technology, Haifa 32000, Israel; Department of Chemical Engineering, Technion - Israel Institute of Technology, Haifa 32000, Israel. Electronic address: bianco@tx.technion.ac.il.
authors.forename: Havazelet
authors.initials: H
authors.lastname: Bianco-Peled
mesh_terms: D048271:Chitosan / Q000737:chemistry*; D003432:Cross-Linking Reagents / Q000737:chemistry*; D020100:Hydrogels / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D039823:Iridoids / Q000737:chemistry*; D010316:Particle Size; D013499:Surface Properties
chemical_list: D003432:Cross-Linking Reagents; D020100:Hydrogels; D039823:Iridoids; D048271:Chitosan; C007834:genipin
keywords: Chitosan; Genipin; Hydrogel; Swelling; Syneresis; pH dependent