Effect of the incorporation of amino groups in a glucose‐responsive polymer complex having phenylboronic acid moieties

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Abstract
A novel polymer complex system sensitive to glucose was studied as a candidate material for formulating a chemically regulated insulin release system. A ternary copolymer of N‐vinyl‐2‐pyrrolidone (NVP), 3‐acrylamidophenylboronic acid (AAm‐PBA) and N,N‐dimethylaminopropylacrylamide (DMAPAA) (poly(NVP‐co‐PBA‐co‐DMAPAA)) was synthesized by radical copolymerization. The phenylboronic acid group in this copolymer serves as a glucose sensor moiety. Poly(NVP‐co‐PBA‐co‐DMAPAA) was soluble in water in the pH range of 3–12, in sharp contrast to a binary copolymer of NVP and AAm‐PBA (poly(NVP‐co‐PBA)) which showed solubility only under alkaline aqueous conditions, where the boronic acid group is in a tetrahedral ionized form. The protonated amino group in poly(NVP‐co‐PBA‐DMAPAA) contributed to increase the solubility of the polymer under physiological and acidic aqueous conditions. Furthermore, poly(NVP‐co‐PBA‐co‐DMAPAA) formed a stable polymer complex gel with poly(vinyl alcohol) (PVA) in pH 7.4 phosphate buffered solution due to the formation of a covalent linkage between the boronic acid groups in ternary copolymer and diol units in PVA. The release of myoglobin as model protein from the complex gel was increased immediately after the addition of glucose, due to the transition of gel into sol state, indicating the feasibility of this complex gel as a candidate material for a glucose‐responsive delivery system for insulin.