Directional Freezing of Crosslinked PVP as a Tool for the Generation of Highly Oriented Macroporous Hydrogels

JIMENA S. GONZÁLEZ ; HERNÁN E. ROMEO; CRISTINA E. HOPPE

Riva del Garda

Simposio; IV International Simposium Frontiers in Polymer Science; 2015

The ability to control the crosslinking density, morphology and porosity of hydrophilic polymeric networks is fundamental for the development of advanced functional hydrogels with applications in remediation, drug delivery, tissue engineering, etc. Hydrogels are wet and soft materials constituted by networks of flexible cross-linked chains with a fluid filling their interstitial space. In these materials, degree and kinetics of swelling depends on factors as crosslinking density, chemical nature and porosity. A common way of introducing porosity in polymeric gels is the use of sacrificial templates during network formation. After curing, the material used to generate porosity is removed and the porous structure obtained. Biocompatible cryogenic processes, based on freezing and subsequent freeze-drying, have been widely used for preparation of non-crosslinked polymeric scaffolds. During freezing, the polymer is segregated from the ice phase giving rise to a macroporous structure characterized by ?fences? of matter enclosing ice. This method, named ISISA (ice segregation-induced self-assembly), allows controlling the macroporosity of the final material by tuning freezing conditions. In spite of its potentiality, the possibility of using this processing technique in the structuring of crosslinked networks has been much less investigated. In this work, porous poly(vinylpyrrolidone) (PVP) hydrogels are formed by crosslinking of concentrated polymer solutions by Fenton reactions, followed by ISISA processing after gel formation. PVP is a non-toxic, hydrophilic polymer with a good biocompatibility and high capacity of ion complexation. This polymer can be fast crosslinked by formation of macroradicals followed by recombination reactions through the use of a Fenton reagent. Conditions conducting to well defined macroporosity alligned in the freezing direction are explored. Influence of the structure of the formed gel, freezing conditions and solvent are analyzed and related with the morphology and swelling kinetics of the obtained materials. Finally, the possibility of using these materials for water remediation is evaluated.