Figure 2.

Blood loop model for assessment of activation of innate immunity systems and blood cells induced by nanoparticles (NPs). The model consists of tubing (internal diameter of 4 mm, length of 20 cm) that is covalently coated with heparin. Human blood, freshly drawn and without anticoagulants (2.0 mL) is added together with NPs in final concentration of ranging from 10 ng/mL to 5 µg/mL blood. Thereafter, the tubing is closed to form loops using connectors of stainless steel coated with immobilized heparin and rotated vertically for 60 min at 20 rpm in a 37°C water bath. After or during incubation, aliquots of blood are removed and analyzed for platelet counts (using a cell counter), leukocyte activation (by FACS analysis), and fluid phase markers resulting from activation of the complement, coagulation, contact/kallikrein systems, and release of cytokines and chemokines using various multiplex assays (see text for details). It should be noted that it is not possible to isolate NPs for corona determination after incubation in whole blood since they will adhere to or be phagocyted by leukocytes [61]. An extensive description of the experimental protocol is found in ref [57] and the figure is reproduced with permission from the publisher.