title: Effects of molecular weight on permeability and microstructure of mixed ethyl-hydroxypropyl-cellulose films.
abstract: Films of ethyl cellulose (EC) and water-soluble hydroxypropyl cellulose (HPC) can be used for extended release coatings in oral formulations. The permeability and microstructure of free EC/HPC films with 30% w/w HPC were studied to investigate effects of EC molecular weight. Phase separation during film spraying and subsequent HPC leaching after immersion in aqueous media cause pore formation in such films. It was found that sprayed films were porous throughout the bulk of the films after water immersion. The molecular weight affected HPC leaching, pore morphology and film permeability; increasing the molecular weight resulted in decreasing permeability. A model to distinguish the major factors contributing to diffusion retardation in porous films showed that the trend in permeability was determined predominantly by factors associated with the geometry and arrangement of pores, independent of the diffusing species. The film with the highest molecular weight did, however, show an additional contribution from pore wall/permeant interactions. In addition, rapid drying and increasing molecular weight resulted in smaller pores, which suggest that phase separation kinetics affects the final microstructure of EC/HPC films. Thus, the molecular weight influences the microstructural features of pores, which are crucial for mass transport in EC/HPC films.
authors.affiliation: SIK - The Swedish Institute for Food and Biotechnology, Structure and Material Design, PO Box 5401, SE-402 29 Gothenburg, Sweden. helene.andersson@sik.se
authors.forename: Helene
authors.initials: H
authors.lastname: Andersson
authors.forename: Johan
authors.initials: J
authors.lastname: Hjärtstam
authors.forename: Mats
authors.initials: M
authors.lastname: Stading
authors.forename: Christian
authors.initials: C
authors.lastname: von Corswant
authors.forename: Anette
authors.initials: A
authors.lastname: Larsson
mesh_terms: D002482:Cellulose / Q000031:analogs & derivatives* / Q000737:chemistry; D003692:Delayed-Action Preparations / Q000737:chemistry; D016503:Drug Delivery Systems; D008855:Microscopy, Electron, Scanning; D008970:Molecular Weight; D010539:Permeability; D016062:Porosity; D014783:Viscosity
chemical_list: D003692:Delayed-Action Preparations; C013517:ethyl cellulose; D002482:Cellulose; C008079:hydroxypropylcellulose