Anti-thrombotic strategies for microfluidic blood processing.

The redundant mechanisms involved in blood coagulation are crucial for rapid hemostasis. Yet they also create challenges in blood processing in medical devices and lab-on-a-chip systems. In this work, we investigate the effects of both shear stress and hypothermic blood storage on thrombus formation in microfluidic processing. For fresh blood, thrombosis occurs only at high shear, and the glycoprotein IIb/IIIa inhibitor tirofiban is highly effective in preventing thrombus formation. Blood storage generally activates platelets and primes them towards thrombosis via multiple mechanisms. Thrombus formation of stored blood at low shear can be adequately inhibited by glycoprotein IIb/IIIa inhibitors. At high shear, von Willebrand factor-mediated thrombosis contributes significantly and requires additional treatments with thiol-containing antioxidants-such as N acetylcysteine and reduced glutathione-that interfere with von Willebrand factor polymerization. We further demonstrate the effectiveness of these anti-thrombotic strategies in microfluidic devices made of cyclic olefin copolymer, a popular material used in the healthcare industry. This work identifies effective anti-thrombotic strategies that are applicable in a wide range of blood- and organ-on-a-chip applications.

Effect of Ice Nucleation and Cryoprotectants during High Subzero-Preservation in Endothelialized Microchannels.

Cryopreservation is of significance in areas including tissue engineering, regenerative medicine, and organ transplantation. We investigated endothelial cell attachment and membrane integrity in a microvasculature model at high subzero temperatures in the presence of extracellular ice. The results show that in the presence of heterogeneous extracellular ice formation induced by ice nucleating bacteria, endothelial cells showed improved attachment at temperature minimums of -6 °C. However, as temperatures decreased below -6 °C, endothelial cells required additional cryoprotectants. The glucose analog, 3-O-methyl-D-glucose (3-OMG), rescued cell attachment optimally at 100 mM (cells/lane was 34, as compared to 36 for controls), while 2% and 5% polyethylene glycol (PEG) were equally effective at -10 °C (88% and 86.4% intact membranes). Finally, endothelialized microchannels were stored for 72 h at -10 °C in a preservation solution consisting of the University of Wisconsin (UW) solution, Snomax, 3-OMG, PEG, glycerol, and trehalose, whereby cell attachment was not significantly different from unfrozen controls, although membrane integrity was compromised. These findings enrich our knowledge about the direct impact of extracellular ice on endothelial cells. Specifically, we show that, by controlling the ice nucleation temperature and uniformity, we can preserve cell attachment and membrane integrity. Further, we demonstrate the strength of leveraging endothelialized microchannels to fuel discoveries in cryopreservation of thick tissues and solid organs.