In vitro platelet adhesion on polymeric surfaces with varying fluxes of continuous nitric oxide release

Nitric oxide (NO) is released by endothelial cells that line the inner walls of healthy blood vessels at fluxes ranging from 0.5 x 10(-10) to 4.0 x 10(-10) mol cm(-2) min(-1), and this continuous NO release contributes to the extraordinary thromboresistance of the intact endothelium. To improve the biocompatibility of blood-contacting devices, a biomimetic approach to release/generate NO at polymer/blood interfaces has been pursued recently (with NO donors or NO generating catalysts doped within polymeric coatings) and this concept has been shown to be effective in preventing platelet adhesion/activation via several in vivo animal studies. However, there are no reports to date describing any quantitative in vitro assay to evaluate the blood compatibilities of such NO release/generating polymers with controlled NO fluxes. Such a methodology is desired to provide a preliminary assessment of any new NO-releasing material, in terms of the effectiveness of given NO fluxes and NO donor amounts on platelet activity before the more complex and costly in vivo testing is carried out. In this article, we report the use of a lactate dehydrogenase assay to study in vitro platelet adhesion on such NO-releasing polymer surfaces with varying NO fluxes. Reduced platelet adhesion was found to correlate with increasing NO fluxes. The highest NO flux tested, 7.05 (+/-0.25) x 10(-10) mol cm(-2) min(-1), effectively reduced platelet adhesion to nearly 20% of its original level (from 14.0 (+/-2.1) x 10(5) cells cm(-2) to 2.96 (+/-0.18) x 10(5) cells cm(-2)) compared to the control polymer coating without NO release capability.