Novel Method Using a Temperature-Sensitive Polymer (Methylcellulose) to Thermally Gel Aqueous Alginate as a pH-Sensitive Hydrogel

A novel method using a temperature-sensitive polymer (methylcellulose) to thermally gel aqueous alginate blended with distinct salts (CaCl<INF>2</INF>, Na<INF>2</INF>HPO<INF>4</INF>, or NaCl), as a pH-sensitive hydrogel was developed for protein drug delivery. It was noted that the salts blended in hydrogels may affect the structures of an entangled network of methylcellulose and alginate and have an effect on their swelling characteristics. The methylcellulose/alginate hydrogel blended with 0.7 M NaCl (with a gelation temperature of 32 °C) demonstrated excellent pH sensitivity and was selected for the study of release profiles of a model protein drug (bovine serum albumin, BSA). In the preparation of drug-loaded hydrogels, BSA was well-mixed to the dissolved aqueous methylcellulose/alginate blended with salts at 4 °C and then gelled by elevating the temperature to 37 °C. This drug-loading procedure in aqueous environment at low temperature may minimize degradation of the protein drug while achieving a high loading efficiency (95−98%). The amount of BSA released from test hydrogels was a function of the amount of alginate used in the hydrogels. The amount of BSA released at pH 1.2 from the test hydrogel with 2.5% alginate was relatively low (20%), while that released at pH 7.4 increased significantly (86%). In conclusion, the methylcellulose/alginate hydrogel blended with NaCl could be a suitable carrier for site-specific protein drug delivery in the intestine.