International Journal of Pharmaceutics 301 (2005) 102–111 Dynamic swelling behavior of -radiation induced polyelectrolyte poly(AAm-co-CA) hydrogels in urea solutions Erdener Karada ˘ g a,∗ , ¨ Omer Barıs ¸ ¨ Uz¨ um a , Dursun Saraydin b , Olgun G ¨ uven c a Adnan Menderes University, Fen-Edebiyat Faculty, Department of Chemistry, 09010 Aydın, Turkey b Cumhuriyet University, Department of Chemistry, 58140 Sivas, Turkey c Hacettepe University, Department of Chemistry, 06532 Beytepe, Ankara, Turkey Received 19 December 2004; received in revised form 3 May 2005; accepted 10 May 2005 Available online 12 July 2005 Abstract The aim of this study was to investigate the equilibrium swelling properties in urea solutions of -radiation induced poly- electrolyte copolymeric hydrogels consisting of acrylamide (AAm) and crotonic acid (CA). Poly(acrylamide-co-crotonic acid), poly(AAm-co-CA) hydrogels containing different amounts of CA were obtained in the form of rods after radiation. Swelling experiments were performed in aqueous urea solutions at 25 ◦ C, gravimetrically. The hydrogels showed large extents of swelling in aqueous (urea/water) media the swelling being highly dependent on the chemical composition of the hydrogels and irradiation dose. The percentage swelling of poly(AAm-co-CA) hydrogels was between 1160 and 4250%, while that of the AAm hydrogels was between 670 and 900%. The diffusional exponent values (n) are between 0.51 and 0.66, hence the diffusion of urea/water into the hydrogels is non-Fickian. Equilibrium urea/water contents of the hydrogel systems were changed between 0.870 and 0.977. © 2005 Elsevier B.V. All rights reserved. Keywords: -Radiation; Swelling; Diffusion; Acrylamide/crotonic acid; Hydrogel; Urea 1. Introduction Hydrogels are polymers in a three-dimensional network arrangement, able to retain large amounts of water. In order to keep the spatial structure, the polymer chains are usually physically or chemically ∗ Corresponding author. Tel.: +90 256 2128498; fax: +90 256 2135379. E-mail address: ekaradag@adu.edu.tr (E. Karada ˘ g). crosslinked. The importance of hydrogels in the bio- material field is justified by some unique characteris- tics: the elastomeric and soft nature of the hydrogels minimizes mechanical and frictional irritation to the tissues and the very low interfacial tension contributes to reducing protein adsorption and cell adhesion. Due to their swelling capacity, hydrogels can be easily rinsed to remove reagent residues. On the other hand, the large water content makes hydrogels a special class of mate- rials. Their network structure is the result not only of 0378-5173/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.ijpharm.2005.05.026