Temperature-dependent modulation of blood platelet movement and morphology on poly(N-isopropylacrylamide)-grafted surfaces

Poly(N-isopropylacrylamide) (PIPAAm) exhibits a reversible, temperature-dependent soluble/insoluble transition at its lower critical solution temperature (LCST) of 32°C in aqueous media. The temperature-responsive PIPAAm was grafted onto tissue culture polystyrene (TCPS) dish surfaces by electron beam irradiation. Blood platelet behaviors on PIPAAm-grafted surface were examined by computerized image analysis and scanning electron microscopy. Platelet behaviors on this surface were dramatically dependent upon temperature, but those on poly(ethylene glycol)(PEG)-grafted or polystyrene remained unchanged. Below the 32°C (LCST), platelets on PIPAAm-grafted surfaces retained a rounded shape and an oscillating vibratory microbrownian motion for extended times, similarly to those on PEG-grafted surfaces. Above the LCST, platelets readily adhered, spread and developed characteristic pseudopodia on PIPAAm-grafted surface similarly to those on TCPS. An ATP synthesis inhibitor failed to hinder prevention of platelet adhesion onto PIPAAm-grafted surface (below the LCST) suggesting that the preventive mechanism is ATP-independent similarly to that of PEG-grafted surfaces. These results correlate platelet surface activation state with the hydration and structure of polymer surfaces, and demonstrate the ability to modulate such reactions by a small temperature change in situ.