FLORY-HUGGINS INTERACTION PARAMETER FOR PVA-WATER IN HYDROGELS PREPARED BY TWO METHODS: FREEZING/THAWING AND CROSSLINKING WITH CITRIC ACID

PVA hydrogels are largely used for biomedical applications due to their biodegradability, biocompatibility, and suitable mechanical strength. These hydrogels can be synthetized by several methods. In this work hydrogels were obtained by two methods, freezing/thawing, and crosslinking with citric acid. The degree of swelling for both types of hydrogels was in the range of 60-70% which corresponds to a medium degree of swelling. Young’s modulus measurements gave values in the range of 0.20 to 4.00 MPa, which are proper values for tissue regeneration or wound healing applications. Crosslinking degree was found to be higher for the freezing/thawing hydrogels, in agreement with a lower percentage of hydration and a higher modulus. By means of the Flory-Rehner model, the interaction parameter (χ) of PVA - water was calculated. This value depends on the availability of OH groups in the polymer. The highest value of c was found for the hydrogels crosslinked with citric acid, revealing that their water-polymer interactions are weaker than those occurring in freezing/thawing hydrogels, which has more available OH groups. However, values higher than 0.5 were found for both types of hydrogels, indicating insolubility in water; therefore, these values imply mechanical stability in aqueous solutions for a relative long time. It is concluded that freezing/thawing is a more reproducible method, which allows the modulation of the crosslinking degree, perhaps, the most important parameter to be controlled.