Discrete responses of erythrocytes, platelets, and von Willebrand factor to shear

Despite decades of technological advancements in blood-contacting medical devices, complications related to shear flow-induced blood trauma are still frequently observed in clinic. Blood trauma includes haemolysis, platelet activation, and degradation of High Molecular Weight von Willebrand Factor (HMW vWF) multimers, all of which are dependent on the exposure time and magnitude of shear stress. Specifically, accumulating evidence supports that when blood is exposed to shear stresses above a certain threshold, blood trauma ensues; however, it remains unclear how various constituents of blood are affected by discrete shears experimentally. The aim of this study was to expose blood to discrete shear stresses and evaluate blood trauma indices that reflect red cell, platelet, and vWF structure. Citrated human whole blood (n = 6) was collected and its haematocrit was adjusted to 30 ± 2% by adding either phosphate buffered saline (PBS) or polyvinylpyrrolidone (PVP). Viscosity of whole blood was adjusted to 3.0, 12.5, 22.5 and 37.5 mPa·s to yield stresses of 3, 6, 9, 12, 50, 90 and 150 Pa in a custom-developed shearing system. Blood samples were exposed to shear for 0, 300, 600 and 900 s. Haemolysis was measured using spectrophotometry, platelet activation using flow cytometry, and HMW vWF multimer degradation was quantified with gel electrophoresis and immunoblotting. For tolerance to 300, 600 and 900 s of exposure time, the critical threshold of haemolysis was reached after blood was exposed to 90 Pa for 600 s (P < 0.05), platelet activation and HMW vWF multimer degradation were 50 Pa for 600 s and 12 Pa for 300 s respectively (P < 0.05). Our experimental results provide simultaneous comparison of blood trauma indices and thus also the relation between shear duration and magnitude required to induce damage to red cells, platelets, and vWF. Our results also demonstrate that near-physiological shear stress (<12 Pa) is needed in order to completely avoid any form of blood trauma. Therefore, there is an urgent need to design low shear-flow medical devices in order to avoid blood trauma in this blood-contacting medical device field.