Permeability control of glucose-sensitive nanoshells.

To study the permeability of hydrogel in nanoscale thickness, core-shell microgels with degradable poly( N-isopropylacrylamide) (PNIPAM) as the core and nondegradable phenylboronic acid (PBA)-conjugated poly( N-isopropylacrylamide) [P(NIPAM-PBA)] as the shell were designed and synthesized. Laser light scattering was used to study the volume phase transitions and core degradation behavior of the core-shell microgels. The release of the degraded core polymer chains can be conveniently followed by turbidity change. At room temperature, the degraded polymer segments diffuse freely out of the precursor poly( N-isopropylacrylamide-co-acrylic acid) gel shells in water. In contrast, the PBA-modified P(NIPAM-PBA) nanoshell can hold most of the degraded core polymer chains under the same conditions, thanks to its condensed structure at the collapsed state. Lowering the temperature or increasing pH increases the swelling degree of the P(NIPAM-PBA) shell, which provides methods to control its permeability by temperature and pH. The complexation of PBA groups with glucose also enhances the swelling of the nanoshell and, thus, increases its permeability. The understanding of how to control the permeability of the glucose-sensitive gel nanoshell in hollow microgel particles is very important for further design of self-regulated insulin delivery systems.