Synthesis and characterization of new hydrogels with pH-dependent swelling properties. Possible applications as biomaterials

JULIO C. CUGGINO; GERMAN CHARLES; MIRIAM C. STRUMIA; CECILIA ALVAREZ IGARZABAL

Rosario, Santa Fe

Workshop; First Workshop on Artificial Organs, Biomaterials and Tissue Engineering (BIOMAT); 2009

Unesco Chair in Criobiology and SLABO

Hydrogels are polymeric materials that exhibit the ability to absorb huge volumes of water. In addition, the water absorption is reversible and dependent of the swelling conditions (pH, T, etc). As consequence of these properties, these kind of polymeric network have received attention as materials for biological, biomedical, pharmaceutical and agricultural applications. The knowledge of the swelling, the diffusion processes, the networks parameters that define its structure and the rheological properties in different conditions are very important since they will define their possible applications. In this work we present the synthesis and characterization of new hydrogels based in a new dendritic monomer with three acid groups (synthesized in our laboratory) with different amount of a crosslinking agent. Besides, thinking in useful application the studies of their properties were examined. The amount of fluid absorbed was evaluated for each hydrogel in water and at different pH. The swelling behavior was dependent of the amount of crosslinking agent and the pH of the fluid absorbed. More amount of crosslinking agent into hydrogel structures presented less equilibrium swelling ratio capacity (%SRe)in all swelling media. The major %SRe was obtained in deionizated water. Besides, the hydrogels had different %SRe at distinct pHs (from buffer solutions). The major swelling capacity was found at pH 7 and the minor at pH 3. At pH 7, the hydrogel is negatively charged and produces repulsion of charges that generates expansion of the network and more absorption of fluid. On the other hand, at pH 3 the hydrogel is totally protonated and the repulsion charge effect disappears, so the hydrogels are less swelled. The elastic moduli G´ of the swelled matrices (at 25ºC in deionized) water were measured in a rotational rheometer. The strain sweeps and frequency sweeps tests were performed on each sample to determine the linear viscoelastic region profiles and viscoelastic performance in a range of frequencies. As expect, the material with more amount of crosslinking agent presented a critical shear stress (limit of linear response) some times larger than the other hydrogels. The frequency sweep test showed that the storage modulus are practically not influenced by the frequency of oscillation for the hydrogels in the range of frequency assayed (0.1-100 s-1). The hydrogels developed in this study exhibit pHdependent swelling and good viscoelastic properties suggesting that they have potential applications in various fields.