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

Poly(N-isopropylacrylamide) (PIPAAm) exhibits a reversible, temperature-dep endent soluble/insoluble transition at its lower critical solution temperat ure (LCST) of 32 degrees C in aqueous media. The temperature-responsive PIP AAm was grafted onto tissue culture polystyrene (TCPS) dish surfaces by ele ctron beam irradiation. Blood platelet behaviors on PIPAAm-grafted surface were examined by computerized image analysis and scanning electron microsco py. Platelet behaviors on this surface were dramatically dependent upon tem perature, but those on poly(ethylene glycol)(PEG)-grafted or polystyrene re mained unchanged. Below the 32 degrees C (LCST), platelets on PIPAAm-grafte d surfaces retained a rounded shape and an oscillating vibratory microbrown ian motion for extended times, similarly to those on PEG-grafted surfaces. Above the LCST, platelets readily adhered, spread and developed characteris tic pseudopodia on PIPAAm-grafted surface similarly to those on TCPS. An AT P synthesis inhibitor failed to hinder prevention of platelet adhesion onto PIPAAm-grafted surface (below the LCST) suggesting that the preventive mec hanism 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. (C) 2000 Elsevier Science Ltd. All rights reserved.