PVA-DNA Cryogel Membranes: Characterization, Swelling, and Transport Studies Adina Papancea, ²,‡ Artur J. M. Valente,* ,² Silvia Patachia, ‡ Maria G. Miguel, ² and Bjo ¨rn Lindman ²,§ Department of Chemistry, UniVersity of Coimbra, 3004-535 Coimbra, Portugal, Department of Chemistry, “TransilVania” UniVersity of BrasoV, 29 Eroilor Str., 500036 BrasoV, Romania, and Physical Chemistry 1, Lund UniVersity, P.O. Box 124, SE-221 00 Lund, Sweden ReceiVed August 27, 2007. In Final Form: October 19, 2007 Double-stranded (ds) DNA from salmon testes has been incorporated into PVA hydrogels obtained by a technique of repeated freezing and thawing. The cryogels obtained are free of potential toxic species like chemical cross-linkers, and consequently, they can be used in pharmaceutical or medical applications. These cryogels show a good mechanical resistance and a white and opaque appearance caused by a heterogeneous porous structure. Encapsulated DNA molecules can be in a compacted or an extended conformation in the PVA matrix and can be controlled by tailoring the degree of crystallinity of the PVA network; this is supported by fluorescence microscopy and UV and FTIR spectroscopic studies. The two forms of encapsulated DNA were observed for different types of matrixes: an extended one in a more crystalline network and a globular one in a more amorphous one. Different associations of base pairs have also been observed. PVA cryogel crystallinity could be tailored by the cryogel contact with different salt solutions. Cryogel surface (scanning electron microscopy) and bulk morphology (porosimetry), swelling, DNA retention, and delivery kinetics have also been studied. All these investigations clearly show strong interactions between PVA and DNA. 1. Introduction Poly(vinyl alcohol) (PVA) is a polymer of great interest because of its many desirable characteristics specifically for various biomedical and pharmaceutical applications. 1 PVA hydrogels are nontoxic, noncarcinogenic, show bioadhesive characteristics, and are easily processed. 2 Furthermore, PVA gels exhibit a high degree of swelling in water and a rubbery and elastic nature. Because of all these features PVA is an excellent basis for biomaterials. In fact, PVA is capable of simulating natural tissues and can be readily accepted into the body. 3 PVA gels have been used for contact lenses, 4 the lining for artificial organs, 5 and drug delivery applications. 6 PVA gels can be prepared by chemical or physical cross- linking; general methods for chemical cross-linking are the use of chemical cross-linkers or the use of electron beam or γ-radiation, whereas the most common method to produce physical cross-linking in PVA is the so-called “freezing-thawing” process. 1 The “freezing-thawing” method addresses toxicity issues because it does not require the presence of a cross-linking agent, and consequently, no toxicity agents are leaching out from the gel matrix. Furthermore, these physically cross-linked materials also exhibit higher mechanical strength and elasticity than PVA gels prepared by other methods. 7,8 These properties are extremely important for the application of PVA gels in biomedical and pharmaceutical fields. Among biological polyelectrolytes, DNA has always attracted particular interest, and there are numerous studies of the interactions between DNA and polycations. Positively charged agents interact predominantly by electrostatic interactions with DNA molecules and induce DNA compaction, aggregation, and precipitation. Studies of DNA condensation have been performed with cationic surfactants, 9-12 liposomes, 13-16 catanionic vesicles, 17-19 and other oppositely charged polymer. 20,21 Theoretical work concerning simulations of DNA/polycation systems has been performed in order to understand interactions between the oppositely charged molecules, in particular compaction and confinement in solution 22,23 and at interfaces. 19,24 A systematic * Corresponding author. Phone: +351 239854459. Fax: +351 239 827703. E-mail: avalente@ci.uc.pt. ² University of Coimbra. ‡ “Transilvania” University of Brasov. § Lund University. (1) Hassan, C. M.; Peppas, N. A. AdV. Polym. Sci. 2000, 153, 37-65. 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