Biomaterials 26 (2005) 3783–3791 A potentiostatic study of oxygen transport through poly (2-ethoxyethyl methacrylate-co-2,3-dihydroxypropylmethacryla hydrogel membranes Vicente Compan ˜ a, , Pilar Tiemblo b , F. Garcı ´a c , J.M. Garcı´a c , Julio Guzma ´n b , Evaristo Riande b a Departamento Termodinamica Aplicada Universidad Polite ´ cnica de Valencia, Camino de Vera s/n. 46020-Valencia, Spain b Instituto de Ciencia y Tecnologı ´a de Polı ´meros, 28006 Madrid, Spain c Universidad de Burgos, Plaza Misael Ban˜uelos s/n, 09001 Burgos, Spain Received 7 September 2004; accepted 23 September 2004 Available online 11 November 2004 Abstract The oxygen permeability and diffusion coefficients of hydrogelmembranesprepared with copolymers of 2-ethoxyethyl methacrylate (EEMA)/2,3-dihydroxypropylmethacrylate (MAG) with mole fraction of the second monomer in the range betw and 0.75 are described. Values of the permeability and diffusion coefficients of oxygen are determined by using electrochemi procedures involvingthe measurement of the steady-state current in membranesprepared by radical polymerization of the monomers. The results obtained for the transport properties were analyzed takinginto account the fractional free volumes, the cohesive energy densities and the glass transition temperatures of the hydrogels. r 2004 Elsevier Ltd. All rights reserved. Keywords: Oxygen permeability; Hydrogel membranes; Oxygen diffusion; Fractional free volume 1. Introduction Hydrophilic polymersprepared from very different monomershavebeen widely investigated in the last decadesgiven thevast field of their applicationsin contact lenses, dental materials, optical lenses, materials for encapsulatedcells, carriersfor controlleddrug delivery, and superabsorbent hydrogels [1–5] to be used in agriculture, medicine, etc.Many differentchemical structures constitute the base of this kind of compounds, although basically it is indispensable that the principal componenthas a hydrophilic character. Particularly, hydrophilic or hydrosoluble methacrylic monomers are used very often to prepare hydrogelsand more particularly for a great part of the polymers used as membranes for soft contact lenses. Recent researches on soft contact lenses are addressed to the development of materials with improved water absorption and minimal dehydration duringthe wear cycle,which is obtained by means of 2-hydroxyethyl methacrylate(HEMA)-2,3-dihydroxypropylmethacry- late (MAG) copolymers. The increase in both properties in lenses made with these copolymers in comparison to conventional lenses of poly(2-hydroxyethylmetacrylate) is due to the strongerintermolecular interactions between water and the hydrophilic moieties in MAG [6]. Therefore, the major interest in these polymeric films is habituallydevotedto developingmaterialswith improved oxygen permeability, dimensionalstability and good mechanical properties in the water-swelled state.Raw materialsused in the preparation of soft contactlenses should give optically transparent films, ARTICLE IN PRESS www.elsevier.com/locate/biomaterials 0142-9612/$ - see front matter r 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.biomaterials.2004.09.061 Correspondingauthor. Tel.: +34 963 8793 28; fax: +34 96 3877 329. E-mail address: vicommo@ter.upv.es (V. Compan ˜).