Microchannels fabricated by soft lithography have been favourable in mechanobiological applications for cell culture platforms, especially shear stress studies. Normally, physiological shear stress levels for veins are between 10 and 70 dynes/cm 2 (1-7 Pa) and arteries between 1 and 6 dynes/cm 2 (0.1-0.7 Pa). In this work, a circular system has been set up by microfluidic pump to mimic physiological environment of monocyte cells for monitoring structural changes at various levels of shear stresses. Shear stresses at 4, 15 and 45 Pa, low, medium and high stresses, respectively, simulated by CFD have been applied on THP-1 cells under different flow rates for 0.5 and 3 h. These cells, which passed through microchannels under these experimental conditions were analysed for their F-actin content by staining with phalloidin and determination of mean fluorescence intensity by fluorescence microscopy and flow cytometry. An increase in THP-1 monocytic cell actin polymerisation is significant in the case of 15 Pa, and slight in the case of 45 Pa shear stress conditions for 0.5 h. This may reflect the structural adaptation of monocytes during a pathological condition such as atherosclerosis.
Atherosclerosis is a long-term disease process of the vascular system that is characterized by the formation of atherosclerotic plaques, which are inflammatory regions on medium and large-sized arteries. There are many factors contributing to plaque formation, such as changes in shear stress levels, rupture of endothelial cells, accumulation of lipids, and recruitment of leukocytes. Shear stress is one of the main factors that regulates the homeostasis of the circulatory system; therefore, sudden and chronic changes in shear stress may cause severe pathological conditions. In this study, microfluidic channels with cavitations were designed to mimic the shape of the atherosclerotic blood vessel, where the shear stress and pressure difference depend on design of the microchannels. Changes in the inflammatory-related molecules ICAM-1 and IL-8 were investigated in THP-1 cells in response to applied shear stresses in an continuous cycling system through microfluidic channels with periodic cavitations. ICAM-1 mRNA expression and IL-8 release were analyzed by qRT-PCR and ELISA, respectively. Additionally, the adhesion behavior of sheared THP-1 cells to endothelial cells was examined by fluorescence microscopy. The results showed that 15 Pa shear stress significantly increases expression of ICAM-1 gene and IL-8 release in THP-1 cells, whereas it decreases the adhesion between THP-1 cells and endothelial cells.
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