Publications

The adhesion of circulating cancer cells to vascular endothelium is a key step in hematogenous metastasis. Cancer cell-endothelium interactions are mediated by cell adhesion molecules that can also be involved in the arrest of circulating leukocytes on endothelium in inflammation. Static and microfluidic flow adhesion assays as well as flow cytometry were conducted in this study to elucidate the role of circulating monocytes, bacterial lipopolysaccharide (LPS), and histamine in breast cancer cell adhesion to vascular endothelial cells. Tumor necrosis factor-α (TNF-α) released from LPS-treated monocytes triggered the expression of intercellular cell adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) on endothelial cells. Histamine augmented the TNF-α effect, leading to a high number of arrested breast cancer cells under both static and shear flow conditions. LPS-treated monocytes were shown to enhance the arrest of breast cancer cells by anchoring the cancer cells to activated endothelial cells. This anchorage was achieved by binding cancer cell ICAM-1 to monocyte β₂ integrins and binding endothelial ICAM-1 and VCAM-1 to monocyte β₁ and β₂ integrins. The results of this study imply that LPS is an important risk factor for cancer metastasis and that the elevated serum level of histamine further increases the risk of LPS-induced cancer metastasis. Preventing bacterial infections is essential in cancer treatment, and it is particularly vital for cancer patients affected by allergy.

Microfluidic cell adhesion assays have emerged as a means to increase throughput as well as reduce the amount of costly reagents. However as dimensions of the flow chamber are reduced and approach the diameter of a cell (Dc), theoretical models have predicted that mechanical stress, force, and torque on a cell will be amplified. We fabricated a series of microfluidic devices that have a constant width:height ratio (10:1) but with varying heights. The smallest microfluidic device (200µm x 20µm) requires perfusion rates as low as 40 nL/min to generate wall shear stresses of 0.5 dynes/cm2. When neutrophils were perfused through P-selectin coated chambers at equivalent wall shear stress, rolling velocities decreased by approximately 70% as the ratio of cell diameter to chamber height (Dc/H) increased from 0.08 (H=100µm) to 0.40 (H=20µm). Three-dimensional numerical simulations of neutrophil rolling in channels of different heights showed a similar trend. Complementary studies with PSGL-1 coated microspheres and paraformaldehyde-fixed neutrophils suggested that changes in rolling velocity were related to cell deformability. Using interference reflection microscopy, we observed increases in neutrophil contact area with increasing chamber height (9-33%) and increasing wall shear stress (28-56%). Our results suggest that rolling velocity is dependent not only on wall shear stress but also on the shear stress gradient experienced by the rolling cell. These results point to the Dc/H ratio as an important design parameter of leukocyte microfluidic assays, and should be applicable to rolling assays that involve other cell types such as platelets or cancer cells.

Background and Purpose: The treatment of vertebro-basilar junction (VBJ) giant aneurysms (GA) remains a challenging task in the neurosurgical practice and the gold standard therapy is still under debate. Through a detailed post-mortem study, the authors analyze the hemodynamic factors underlying the formation and recanalization of an aneurysm located at this particular site and its anatomic configuration.
Methods: An adult fixed cadaveric specimen with a known VBJ GA, characterized radiographically and treated with endovascular embolization, was studied. 3-D computational fluid dynamic (CFD) models were built based on the specific angio-architecture of the specimen and each step of the endovascular treatment was simulated.
Results: The 3-D CFD study showed at the neck region of the aneurysm, an area of hemodynamic stress (high wall shear stress, high static pressure, high flow velocity), matching the site of recanalization seen during the treatment period of the patient.
Conclusions: Aneurysm morphology, location and patient specific angio-architecture are the principal factors to be considered in the management of the VBJ giant aneurysms. The 3-D CFD study is valuable tool that, coupled with the neuro-radiological work-up, may add valuable insights in the treatment planning of complex cerebrovascular diseases.

Histamine and tumor necrosis factor-α (TNF-α) are critical mediators of acute and chronic inflammation that are generated by mast cells and macrophages in atherosclerotic lesions or systemically during allergic attacks. Both of them induce activation of vascular endothelium and thus may play a role in thrombosis. Here we studied the interplay between histamine and TNF-α in glycoprotein (GP) Ibα-mediated platelet adhesion to cultured human vascular endothelial cells under static and shear flow conditions. The stimulation of endothelial cells with histamine or TNF-α increased the number of adherent or slow rolling GP Ibα-coated microbeads or washed human platelets. However, the application of histamine to endothelium pre-activated by TNF-α inhibited GP Ibα-mediated platelet adhesion. These effects were found to be associated with changes in the concentration of ultra large von Willebrand factor (ULVWF) strings anchored to endothelium. The results of this study indicate that histamine released during mast cell degranulation may cause or inhibit thrombosis, depending on whether it acts on resting endothelial cells or on cells pre-activated by other inflammatory stimuli.

The histamine level is high during allergic attacks, and patients with allergy may have chronic inflammatory conditions at which tumor necrosis factor (TNF)-α is extensively released by macrophages. Here, in vitro static and microfluidic flow assays were conducted to investigate the combined influence of histamine and TNF-α on adhesion of monocytic THP-1 cells to human umbilical vein endothelial cells (HUVEC). In a static assay, histamine stimulation of TNF-α-activated HUVEC elevated the number of attached THP-1 cells. In a flow assay, the number of crawling and firmly adherent THP-1 cells was higher on TNF-α + histamine activated HUVEC than on HUVEC activated by TNF-α alone. This synergistic effect of histamine and TNF-α is caused by the increased endothelial surface expression of intercellular adhesion molecule-1, vascular cell adhesion molecule-1, and E-selectin. Since the exposure of TNF-α-activated endothelium to histamine favors monocyte recruitment, it may be a serious risk factor for atherosclerosis and other chronic inflammatory disorders.

The effects of cell size and deformability on the lateral migration and deformation of living cells flowing through a rectangular microchannel has been numerically investigated and compared with the experimental data on the inertial microfluidics-based approach for detection and separation of cells. The results of this work indicate that the cells move closer to the centerline if they are bigger and/or more deformable and that their equilibrium position is largely determined by the solvent (cytosol) viscosity, which is much less than the polymer (cytoskeleton) viscosity measured in most rheological systems. Simulations also suggest that decreasing channel dimensions leads to larger differences in equilibrium position for particles of different viscoelastic properties, giving design guidance for the next generation of microfluidic cellseparation chips.

The endovascular treatment of intracranial aneurysms remains a challenge, especially when the aneurysm is large in size and has irregular, non-spherical geometry. In this paper, we use computational fluid dynamics to simulate blood flow in a vertebro-basilar junction giant aneurysm for the following three cases: 1) an empty aneurysm, 2) an aneurysm filled with platinum coils, and 3) an aneurysm filled with a yield stress fluid material. In the computational model, blood and the coil-filled region are treated as a non-Newtonian fluid and an isotropic porous medium, respectively. The results show that yield stress fluids can be used for aneurysm embolization provided the yield stress value is 20 Pa or higher. Specifically, flow recirculation in the aneurysm and the size of the inflow jet impingement zone on the aneurysm wall are substantially reduced by yield stress fluid treatment. Overall, this study opens up the possibility of using yield stress fluids for effective embolization of large-volume intracranial aneurysms.

Multicellular tumor spheroids are widely used as in vitro models for testing of anticancer drugs. The advantage of this approach is that it can predict the outcome of a drug treatment on human cancer cells in their natural three-dimensional environment without putting actual patients at risk. Several methods were utilized in the past to grow submillimeter-size tumor spheroids. However, these small models are not very useful for preclinical studies of tumor ablation where the goal is the complete destruction of tumors that can reach several centimeters in diameter in the human body. Here, we propose a PDMS well method for large tumor spheroid culture. Our experiments with HepG2 hepatic cancer cells show that three-dimensional aggregates of tumor cells with a volume as large as 40 mm³ can be grown in cylindrical PDMS wells after the initial culture of tumor cells by the hanging drop method. This is a 320 times more than the maximum volume of tumor spheroids formed inside hanging drops (0.125 mm³).

Cavitation activity and temperature rise have been investigated in a tissue-mimicking material and excised bovine liver treated with ethanol and insonated with a 0.825 MHz focused acoustic transducer. The acoustic power was varied from 1.3 W to 26.8 W to find the threshold leading to the onset of inertial cavitation. Cavitation events were quantified by three independent techniques: B-mode ultrasound imaging, needle hydrophone measurements, and passive cavitation detection. Temperature in or near the focal zone was measured by thermocouples embedded in the samples. The results of this study indicate that the treatment of tissue phantoms and bovine liver samples with ethanol reduces their threshold power for inertial cavitation. This in turn leads to a sudden rise in temperature in ethanol-treated samples at a lower acoustic power than that in untreated ones. The analysis of passive cavitation detection data shows that once the threshold acoustic power is reached, inertial cavitation becomes a major contributor to acoustic scattering in ethanol-treated phantoms and bovine liver samples as compared to control. This study opens up the possibility of improved tumour ablation therapy via a combination of percutaneous ethanol injection and high-intensity focused ultrasound.

There is a need for accurate yield stress measurements, especially in the case of low yield stress complex materials such as biological samples. This task cannot be accomplished with conventional rotational rheometers due to significant wall slip effects and the necessity to operate the device at very low shear rates, often beyond the limit that such rheometers can achieve. In this paper, we focus on the slotted plate method proposed recently for low yield stress measurements. Using computational fluid dynamics, we study the effects of plate geometry on the measurement accuracy of the slotted plate method. Results of this study indicate that both wall slip effects and pressure drag force can be substantially reduced by adopting a thin plate with sharp front and rear edges, high slot area ratio, and large number of slots. If the plate has 30 degree triangular edges, a slot area ratio of 80%, and 12 slots, the slotted plate method overpredicts the yield stress of a 0.09 wt.% Carbopol dispersion (yield stress of 9.17 Pa) by only 8.4% under no slip conditions and underpredicts the yield stress by 12.3% under free slip conditions. Similar results were obtained for human saliva characterized by a very low yield stress (0.073 Pa).