title: Development of novel nonaqueous ethylcellulose gel matrices: rheological and mechanical characterization.
abstract: OBJECTIVE
  This study reports the rheological and mechanical characterization of novel non-aqueous ethylcellulose gel matrices intended for topical drug delivery. An attempt was also made to explain the molecular interaction within the gel systems from a molecular conformational approach.
  
  
  METHODS
  Nonaqueous gel matrices were prepared from three fine particle grades of ethylcellulose and propylene glycol dicaprylate/dicaprate. Continuous and oscillatory shear rheometry was performed using a cone-and-plate rheometer and mechanical characterization was performed using a universal tensile tester.
  
  
  RESULTS
  The gel matrices exhibited prominent viscoelastic behaviour, yield stress and thixotropy. Rheological and mechanical properties showed significant upward trends with increased polymeric chain length and polymer concentrations. Good linear correlations were obtained between rheological and mechanical properties. The solvent molecular conformation was found to play a role in affecting the formation of gel networks via intermolecular hydrogen bonding between ethylcellulose polymer chains.
  
  
  CONCLUSIONS
  Ethylcellulose was successfully formulated as a nonaqueous gel with propylene glycol dicaprylate/dicaprate. The novel nonaqueous gel exhibited rheological profiles corresponding to a physically cross-linked three dimensional gel network, with suitable mechanical characteristics for use as a vehicle for topical drug delivery. Molecular conformation of the solvent was found to influence the molecular interactions associated with formation of ethylcellulose gel networks.
authors.affiliation: Department of Pharmacy, Faculty of Science, National University of Singapore, 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: K T
authors.initials: KT
authors.lastname: Chow
mesh_terms: D000268:Adhesiveness; D000287:Administration, Topical; D002482:Cellulose / Q000031:analogs & derivatives* / Q000737:chemistry; D019245:Compressive Strength; D016503:Drug Delivery Systems; D005782:Gels / Q000138:chemical synthesis / Q000737:chemistry*; D006244:Hardness; D008968:Molecular Conformation; D011409:Propylene Glycols / Q000737:chemistry; D012212:Rheology; D033081:Shear Strength
chemical_list: D005782:Gels; D011409:Propylene Glycols; C013517:ethyl cellulose; D002482:Cellulose