No abstract

By the functionalization of poly(N-isopropylacrylamide-co-acrylic acid) microgels with 3-aminophenylboronic acid (APBA) via carbodiimide coupling, nearly monodisperse glucose-sensitive P(NIPAM-PBA) microgels with a diameter of several hundred nanometers were synthesized in aqueous media. Dynamic laser light scattering was used to study the glucose-sensitive and thermosensitive behaviors of the resultant microgels under various conditions. The introduction of the hydrophobic phenylboronic acid (PBA) group significantly decreases the volume phase transition temperature of the resultant microgels. As a result, the P(NIPAM-PBA) microgels with a 10.0 mol % PBA content are in a collapsed state at room temperature. However, the addition of glucose makes the microgels swell dramatically. The glucose-sensitivity of the PBA-containing microgels relies on the stabilization of the charged phenylborate ions by binding with glucose, which can convert more hydrophobic PBA groups to the hydrophilic phenylborate ions. The presence of glucose also induces a two-stage volume phase transition of the P(NIPAM-PBA) microgels, which is explained by the core-shell-like heterogeneous structure of the microgels induced by the formation of the unique glucose-bis(boronate) complex in the "core" area of the microgels. The effects of pH, ionic strength, and PBA content on the glucose sensitivity of the P(NIPAM-PBA) microgels were investigated.

Boronic acid-containing hydrogels are important intelligent materials. With the introduction of boronic acid functionality, these hydrogels exhibit a lot of interesting properties, such as glucose-sensitivity, reversibility and self-healing. These materials have found important applications in many areas, especially in biomedical areas. This paper aims to provide an overview of the current state of the art of the study in this area. We review the synthesis and properties of various boronic acid-containing hydrogels, including macroscopic hydrogels, microgels and layer-by-layer self-assembled films. Their applications were described, with an emphasis on the design of various glucose sensors and self-regulated insulin delivery devices. New development in this area was highlighted. Problems and the new directions were discussed.