title: Network structure of cellulose ethers used in pharmaceutical applications during swelling and at equilibrium.
abstract: OBJECTIVE
  The purpose of this work was to investigate the swelling behavior of four cellulose ethers that differ in their type and degree of substitution and to elucidate the network structure of the swollen matrices under dynamic and equilibrium conditions.
  
  
  METHODS
  Dynamic vapor sorption was performed to assess the ability of polymer chains and water molecules to interact. Dynamic and equilibrium swelling studies were performed to calculate molecular parameters of swollen polymers using the Flory-Rehner theory.
  
  
  RESULTS
  We determined the volume-swelling ratio of the polymer matrices and observed that it was dependent on their hydrophilicity. We determined molecular parameters that characterize the swollen hydrogels of cellulose derivatives, such as the polymer volume fraction in the swollen state, u2,S, the effective molecular weight of the polymer chain between physical entanglements, Me, the number of repeating units between two entanglements, u, and the number of entanglements per chain, e. The Me of the cellulose derivatives studied varied significantly depending on the type of cellulose ether and on the swelling time.
  
  
  CONCLUSIONS
  The order of mesh size, an important parameter for predicting drug diffusion and release, taking into account all determined parameters, is: hydroxypropyl cellulose < hydroxyethyl cellulose < hydroxypropyl methyl cellulose K100M < hydroxypropyl methyl cellulose K4M.
authors.affiliation: University of Ljubljana, Faculty of Pharmacy, Slovenia.
authors.forename: Saia
authors.initials: S
authors.lastname: Baumgartner
authors.forename: Julijana
authors.initials: J
authors.lastname: Kristl
authors.forename: Nicholas A
authors.initials: NA
authors.lastname: Peppas
mesh_terms: D002482:Cellulose / Q000737:chemistry*; D004987:Ethers / Q000737:chemistry*; D005782:Gels; D011108:Polymers; D013678:Technology, Pharmaceutical / Q000379:methods*
chemical_list: D004987:Ethers; D005782:Gels; D011108:Polymers; D002482:Cellulose