Controlled release from poly ( vinyl alcohol ) gels prepared by freezing-thawing processes

Reinforced poly (vinyl alcohol) hydrogels were prepared by freezing aqueous solutions of 15 wt% PVA at −20°C for eighteen hours and thawing them at room temperature for six hours. Swelling studies were run on samples that had undergone three, four, and five freezing-thawing cycles. The gels formed after five freezing-thawing cycles were comparatively stronger and more rigid than those formed with fewer cycles. Swelling studies showed that the water uptake increased with time, then slowly decreased. This was indicative of a molecular densification during the freezing-thawing process. Differential scanning calorimetry showed that the degree of crystallinity decreased initially. Release studies were run on reinforced PVA hydrogels with bovine serum albumin which was incorporated before the freezing thawing treatment. Release was followed over nineteen days. The protein transport was modelled by a regular Fickian diffusion model.