title: Viscoelastic properties of a new in situ gelling thiolated chitosan conjugate.
abstract: The aim of this study was the synthesis of a new thiolated chitosan conjugate and the evaluation of its viscoelastic properties in vitro. The modification of chitosan was achieved by covalent attachment of isopropyl-S-acetylthioacetimidate to chitosan. The resulting conjugate (chitosan-TEA; chitosan-thioethylamidine) exhibited 300.7+/-27.4 micromol thiol groups per gram polymer and no disulfide bond. For rheological studies, the pH of 0.5% and 1% polymer solutions was adjusted to 6.5 in order to simulate a physiological pH-level. Both, 0.5% and 1% chitosan-TEA solutions showed the transition from sol to gel within 30 min. Within 6 h of incubation, the storage modulus of 0.5% and 1% chitosan-TEA increased 3354-fold and 6199-fold, whereas the loss modulus increased 11-fold and 38-fold, respectively. Frequency sweep measurements demonstrated an increase in crosslinking of the thiolated polymer as a function of time. The formation of inter- and/or intramolecular disulfide bonds was monitored indirectly via determining the decrease of thiol groups. Unmodified chitosan did not exhibit in situ gelling properties. The release of a fluorescent marker being incorporated in a 0.5% chitosan-TEA solution was significantly (p<0.001) slower, when the formulation was preincubated for one hour and consequently already highly crosslinked. The polymer generated within this study represents a promising novel tool for various drug delivery systems, where in situ gelling properties are advantageous.
authors.affiliation: Institute of Pharmaceutical Technology and Biopharmaceutics, Center of Pharmacy, University of Vienna, Vienna, Austria.
authors.forename: Alexander H
authors.initials: AH
authors.lastname: Krauland
authors.forename: Martin H
authors.initials: MH
authors.lastname: Hoffer
authors.forename: Andreas
authors.initials: A
authors.lastname: Bernkop-Schnürch
mesh_terms: D000465:Algorithms; D048271:Chitosan / Q000737:chemistry*; D003911:Dextrans / Q000737:chemistry; D004220:Disulfides / Q000737:chemistry; D004548:Elasticity; D005079:Excipients / Q000737:chemistry*; D005456:Fluorescent Dyes; D005782:Gels; D006863:Hydrogen-Ion Concentration; D010084:Oxidation-Reduction; D013438:Sulfhydryl Compounds; D014783:Viscosity
chemical_list: D003911:Dextrans; D004220:Disulfides; D005079:Excipients; D005456:Fluorescent Dyes; D005782:Gels; D013438:Sulfhydryl Compounds; D048271:Chitosan