Synthesis, characterization, and evaluation of enzymatically degradable poly( N ‐isopropylacrylamide‐ co ‐acrylic acid) hydrogels for colon‐specific drug delivery

The enzymatically degradable poly( N ‐isopropylacrylamide‐ co ‐acrylic acid) hydrogels were prepared using 4,4 ′ ‐bis(methacryloylamino)azobenzene (BMAAB) as the crosslinker. It was found that the incorporated N ‐isopropylacrylamide (NIPAAm) monomer did not change the enzymatic degradation of hydrogel, but remarkably enhanced the loading of protein drug. The hydrogels exhibited a phase transition temperature between 4°C (refrigerator temperature) and 37°C (human body temperature). Bovine serum albumin (BSA) as a model drug was loaded into the hydrogels by soaking the gels in a pH 7.4 buffer solution at 4°C, where the hydrogel was in a swollen status. The high swelling of hydrogels at 4°C enhanced the loading of BSA (loading capability, ca . 144.5 mg BSA/g gel). The drug was released gradually in the pH 7.4 buffer solution at 37°C, where the hydrogel was in a shrunken state. In contrast, the enzymatic degradation of hydrogels resulted in complete release of BSA in pH 7.4 buffer solution containing the cecal suspension at 37°C (cumulative release: ca . 100 mg BSA/g gel after 4 days). Copyright © 2008 John Wiley & Sons, Ltd.