Permeation control by thermosensitive shell layer of submicron microspheres

Monodisperse microspheres composed of ubiquinone (UQ)-containing hydrophobic core and thermosensitive hydrogel shell were prepared by soap-free emulsion copolymerization of hydrophobic monomers and N-isopropylacrylamide (NIPAM) in the presence of UQ. Some properties such as hydrodynamic size and electrophoretic mobility of the microspheres showed unique temperature-dependence. The rate of permeation of UQ-reducing and oxidizing agents from aqueous media to the microsphere core through the poly-NIPAM shell was measured as a function of temperature. The rate decreased gradually with increasing temperature and became near zero above the lower critical solution temperature of poly-NIPAM. Thus, a poly-NIPAM shell of microspheres can be regarded as thermo-sensitive ultra-thin membrane.