TEMPERATURE-RESPONSIVE POLY(N-ISOPROPYLACRYLAMIDE) AS A MODULATOR FORALTERATION OF HYDROPHILIC HYDROPHOBIC SURFACE-PROPERTIES TO CONTROL ACTIVATION INACTIVATION OF PLATELETS

Our research is directed toward development and fundamental studies of biomedically relevant modulation systems using the temperature-respon sive polymer, poly(N-isopropylacrylamide) (PIPAAm) functionalized with a carboxyl end group, as the switching element. This material has bee n attached to both biomolecules and solid surfaces to create new, modi fied bioconjugates and grafted surfaces, respectively. PIPAAm was used to introduce a reversible switching function correlated to hydration- dehydration changes of polymer chains in response to changes in temper ature, The introduction of PIPAAm chains onto polymer surfaces is inte nded to impart temperature-responsive surface property changes, These surfaces were prepared using either PIPAAm with a terminal carboxyl en d group or random copolymers of IPAAm with acrylic acid. The effects o f graft conformation on the dynamics of grafted PIPAAm species were in vestigated by means of aqueous dynamic contact angle measurement. Each PIPAAm-grafted surface showed completely hydrophilic nature below 20 degrees C, however, these surfaces become hydrophobic above their crit ical temperature. The extent of hydrophobic property for multipoint-gr afted surfaces was small compared to that of the terminally grafted su rface. These hydrophilic/hydrophobic surface property changes affect t he platelet contact activation. The increase in cytoplasmic [Ca2+](i) in platelets was observed only when PIPAAm grafted surface become hydr ophobic, The feasibility of cell activation/inactivation control by te mperature-modulated surface changes is attractive as modulator for bio medical systems and this strategy may lead to development of new 'inte lligent materials' with specific temperature-modulated surface propert ies.