Monodisperse microspheres with poly(N-isopropylacrylamide) core and poly(2-hydroxyethyl methacrylate) shell.

Monodisperse core-shell microspheres, composed of poly(N-isopropylacrylamide) (PNIPAM) core with thermo-responsive swelling/shrinking function and biocompatible poly(2-hydroxyethyl methacrylate) (PHEMA) shell with "open/close" switching function, have been successfully prepared by microfluidic emulsification, free-radical polymerization and atom transfer radical polymerization (ATRP). The effects of grafting time for the ATRP and polyvinyl alcohol (PVA) concentration inside the core on the thermo-responsive behavior of core-shell microspheres are investigated. For the core-shell microspheres prepared with PVA concentration of 2% (w/v) and grafting time of 2 h, the PNIPAM core is in the shrunken state and the solid PHEMA shell protect the whole PNIPAM core at temperatures above the volume phase transition temperature (VPTT); as environmental temperature decreases below the VPTT, the PNIPAM core swells dramatically and the PHEMA shell ruptures a large area. The thermo-responsive function of the core-shell microspheres is reversible and the appearance/recovery of PHEMA shell crack exhibits an "open/close" switching function. Such core-shell microspheres are highly attractive for developing drug delivery systems with both biocompatible and thermo-responsive characteristics.