(643c) A Novel Smart Microsphere with K+-Induced Shrinking and Aggregating Property Based on Responsive Host-Guest System

A novel type of smart microspheres with K⁺-induced shrinking and aggregating properties is designed and developed based on K⁺-recognition host-guest system.  The microspheres are composed of crosslinked poly(N-isopropylacrylamide-co-acryloylamidobenzo-15-crown-5) (P(NIPAM-co-AAB15C5)) networks.  Due to the formation of stable 2:1 “sandwich-type” host-guest complexes between 15-crown-5 units and K⁺ ions, the P(NIPAM-co-AAB15C5) microspheres significantly exhibit isothermally and synchronously K⁺-induced shrinking and aggregating properties at a low K⁺ concentration; while other cations (e.g., Na⁺, H⁺, NH₄⁺, Mg²⁺ or Ca²⁺) can not trigger such response behaviors.  Effects of chemical compositions of microspheres on the K⁺-induced shrinking and aggregating behaviors are investigated systematically.  The K⁺-induced aggregating sensitivity of the P(NIPAM-co-AAB15C5) microspheres can be enhanced by increasing the content of crown ether units in the polymeric networks; however, it is nearly not influenced by varying the monomer and crosslinker concentrations in the microsphere preparation.  State diagrams of the dispersed-to-aggregated transformation of P(NIPAM-co-AAB15C5) microspheres in aqueous solutions as a function of temperature and K⁺ concentration are constructed, which provide valuable information for tuning the dispersed/aggregated states of microspheres by varying environmental K⁺ concentration and temperature.  The microspheres with synchronously K⁺-induced shrinking and aggregating properties proposed in this study provide a brand-new model for designing novel targeted drug delivery systems.