Preparation of phenylboronic acid-based hydrogel microneedle patches for glucose-dependent insulin delivery

There is a problem with directly loading insulin into the polymerized glucose-responsive microneedle (MN) patch due to that polymerization conditions and solvents may damage the activity of insulin. In this study, we report a totally polymerized phenylboronic acid-based MN patch, and insulin was directly loaded in MNs by a mild drop/dry procedure. MN patch was prepared by copolymerization of N-isopropyl acrylamide,N-vinyl-2-pyrrolidone, and 3-acrylamidoephenylboronic acid in MN mold. The MN patch showed good glucose-dependent swelling behavior in pH 9.0 at 27 degrees C. After insulin loading procedure, insulin was distributed on and within the MNs. About 43.2% of total insulin was diffused into MNs' interior. As a result, the release of insulin on MNs' surface was uncontrolled by MNs and rapidly finished after similar to 10 min. However, the release of insulin within MNs was depended on glucose concentration, and insulin was released 1.6 times more at 4 g/L than at 1 g/L glucose concentration after 12 h. Although further improvements are needed to make MN patch responding in physiological environment, this work suggests a solution for directly loading insulin in polymerized glucose-responsive MNs.