ABSTRACT
Hydrogels represent a special class of hydrophilic polymer materials and are dened as two-or multicomponent systems consisting of a water or aqueous solution, lled three-dimensional network of polymer chains (Hoffman 2002; Rosiak et al. 2002). Hydrogels adsorb signicant amounts of water, from 10 to 20% to several thousand times their dry weight (Hoffman 2002). The amount of water adsorbed depends on the type of polymer and cross-link as well as the cross-link density (Hoffman 2002). The ability of biocompatible hydrogels to adsorb and hold aqueous solutions has been exploited in many biotechnological, biomedical, and pharmaceutical applications over the past 40 years (Peppas et al. 2000; Lozinsky et al. 2003). Hydrogels are commonly used for soft contact lenses, wound dressings, drug delivery systems, and
CONTENTS
9.1 Introduction ................................................................................................ 211 9.2 Determination of the Porosity by Gravimetric Methods ..................... 214
9.2.1 Mercury Porosimetry (MP) .......................................................... 216 9.2.2 Gas Pycnometry ............................................................................. 217 9.2.3 Imaging ........................................................................................... 217 9.2.4 Scanning Electron Microscopy .................................................... 218 9.2.5 X-Ray Microcomputer Tomography ............................................ 221 9.2.6 Magnetic Resonance Imaging (MRI) ..........................................222 9.2.7 Light Microscopy and Confocal Laser
Scanning Microscopy ....................................................................222 9.2.8 Image Analysis ............................................................................... 224
9.3 Determination of the Nanoporous Structure of Hydrogels Using 1H NMR Spectroscopy and Thermally Stimulated Depolarization (TSD) ................................................................................. 226 9.3.1 Gel Permeability .............................................................................228
