Thermally reversible polymer gels for biohybrid artificial pancreas

As an approach to replacing islets of Langerhans in an implanted biohybrid artificial pancreas, thermally reversible polymers based on N-isopropylacrylamide were synthesized and then evaluated as an extracellular matrix for islets in an immunoprotecting membrane pouch. A high molecular weight poly(N-isopropylacrylamide-co-acrylic acid (2 mole % in feed)) demonstrated gelation at 37°C and became a solution below 30°C. This polymer exhibited minimum syneresis (water separation) upon gelation from a solution state when the temperature was raised from room temperature to 37°C, while poly(N-isopropylacrylamide) exhibited considerable syneresis under the same conditions. These properties influence the efficiency of islet entrapment. The copolymer was able to entrap rat islets almost 100%, but the homopolymer entrapped less than 50%. The static insulin secretion of the islets in the copolymer matrix at high glucose concentration (16.5 mM) was comparable to that of control islets, however, the entrapped islets showed prolonged viability in vitro. These results indicate the potential of developing a rechargeable biohybrid pancreas using thermally reversible polymer gels.