Neutrophil extracellular trap formation upon exposure of hydrophobic materials to human whole blood causes thrombogenic reactions
Neutrophil extracellular trap (NET) formation, a reaction of the innate immune system to fight pathogens, was shown to be involved in thrombus formation. In the present study blood-contacting biomaterials with graded surface characteristics were investigated as a potential cause of NET formation on medical devices. Surface properties are known to govern protein adsorption, cell adhesion and ultimately the activation of several other host defense pathways – potentially also the formation of NETs. Model materials of defined hydrophilic or hydrophobic properties (glass, and thin films of poly(ethylene-alt-maleic anhydride), self-assembled monolayers of methyl terminated alkanethiols, and Teflon AF™) were incubated either with isolated human granulocytes after pre-adsorption with plasma proteins or with human whole blood. NET formation – detected as extracellular DNA, citrullinated histones, elastase and reactive oxygen species (ROS) – was observed on hydrophobic surfaces. Furthermore, NET formation on the hydrophobic surface Teflon AF™ resulted in elevated thrombin generation in hirudin-anticoagulated whole blood, but not in heparinized whole blood. Disintegration of surface-bound NETs by DNase treatment resulted in significantly lower pro-coagulant effects. Thus, NET formation can contribute to the thrombogenicity of clinically applied hydrophobic materials, suggesting NETosis as well as NET surface anchorage as new targets of anticoagulation strategies.