title: Kinetics of re-equilibrium of oppositely charged hydrogel-surfactant system and its application in controlled release.
abstract: We report a study of re-equilibrium kinetics of an oppositely charged hydrogel-surfactant system (cationically modified hydroxyethyl cellulose (cat-HEC) and sodium dodecyl sulfate (SDS)) and an application of the formulation for delivery of a water-insoluble molecule. Hydrogels have been applied for long-term delivery of water-soluble drugs due to their controlled-release property. However, the release mechanism of drugs solubilized by surfactants has not been clear. In the present study, SDS was used to solubilize a hydrophobic model drug, and thereafter, by electrostatic interaction between cat-HEC and SDS, the solubilized model drug was loaded into two types of cat-HEC hydrogels with different charge density. We found that the charge density of the polymers had a crucial effect on the loading capacity, without affecting the re-equilibrium kinetics. By an elaborate design of the experiments, the release profiles were fitted with one-dimensional Fickian law where we found the diffusivity of the drug to be constant and comparable to free micelles over a wide region of surfactant concentrations. The observed long-term controlled diffusion is discussed from a thermodynamic point of view.
authors.affiliation: Department of Pharmacy, School of Pharmacy, University of Oslo, Oslo 0316, Norway. wei.wang@farmasi.uio.no
authors.forename: Wei
authors.initials: W
authors.lastname: Wang
authors.forename: Sv Arne
authors.initials: SA
authors.lastname: Sande
mesh_terms: D001391:Azo Compounds / Q000737:chemistry; D002412:Cations; D002482:Cellulose / Q000031:analogs & derivatives* / Q000737:chemistry; D003692:Delayed-Action Preparations; D004058:Diffusion; D020100:Hydrogels / Q000737:chemistry*; D007700:Kinetics; D015394:Molecular Structure; D012967:Sodium Dodecyl Sulfate / Q000737:chemistry*; D055672:Static Electricity; D013501:Surface-Active Agents / Q000737:chemistry*; D014867:Water
chemical_list: D001391:Azo Compounds; D002412:Cations; D003692:Delayed-Action Preparations; D020100:Hydrogels; D013501:Surface-Active Agents; D014867:Water; D012967:Sodium Dodecyl Sulfate; D002482:Cellulose; C002283:hydroxyethylcellulose