In vitro platelet adhesion to nonionic and ionic hydrogels with different water contents

To investigate in vitro platelet adhesion to hydrogels, using electron-beam irradiation, polymer reaction, and radical polymerization, hydrogels were synthesized to have a wide range of water content. The nonionic synthesized hydrogels include polyacrylamide (PAAm), poly(vinyl alcohol) (PVA), poly(ethylene glycol) (PEG), poly(N-vinyl pyrrolidone), and poly(methoxy-PEG methacrylate) while the ionic hydrogels were crosslinked poly(AAm-acrylic acid) and poly(AAm-dimethylaminoethyl methacrylate) copolymers. Adhesion of washed rabbit platelets to these hydrogels were studied in phosphate-buffered saline for 30 min. In the case of PVA and PAAm hydrogels, platelet adhesion also was conducted in the presence of proteins. The protein sorption into PVA hydrogel was studied by fluorescent spectroscopy. It was found that all the nonionic hydrogels exhibited a lower level of platelet adhesion than did conventional hydrophobic polymers, such as medical-grade poly(vinyl chloride), polyurethane, and silicone, and they exhibited the minimum platelet adhesion at a water content of around 90%. PAAm and PEG hydrogels had the weakest interaction with platelets when the water content was lower than 90%. PVA hydrogel showed the highest platelet adhesion in the low-water-content region, but the platelet adhesion was greatly reduced in the presence of proteins. Significant protein sorption was noted when the water content of PVA hydrogel was as high as 80%. Introduction of a positive charge into the PAAm hydrogel promoted platelet adhesion whereas the negative charge introduced into the hydrogel slightly reduced the number of adhered platelets.