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Effect of Cyclic Stretch on the Visco-Elastic Deformation of Endothelial Cells in Micropipette Aspiration Experiment

Javad Hatami; Tafazzoli-Shadpour, Mohammad ; Shokrgozar, Mohammad Ali

Proceedings of the 6th World Congress of Biomechanics (WCB 2010). August 1-6, 2010 Singapore, (2010), 1087-1090

Mechanical environment of arterial endothelial cells (ECs) is an important factor affecting endothelial functionality. Endothelial cells are physiologically exposed to a variety of mechanical stimuli. The aim of this study is to investigate effects of cyclic stretch on the Visco-elastic deformation of ECs utilizing micropipette aspiration experiment.

Human Umbilical Vein Endothelial Cells (HUVECs) were transferred on the central region of silicon membrane precoated with collagen type I. After one night incubation, cells were subjected to uniaxial cyclic stretch utilizing a custom built apparatus. Test conditions included load frequency of 1 Hz, strain amplitudes of 10% and 20%, and test durations of 2, 4, 6 and 8 hours.

Micropipette aspiration experiment was performed after detaching cells from substrate. A linear standard three parameter viscoelastic solid model was used. In this model, the cell is assumed to be a homogeneous, incompressible and viscoelastic material with an applied uniform axisymmetric aspiration pressure. Results of test groups were statistically compared with control groups using ANOVA.

Result showed visco-elastic behavior of ECs in micropipette aspiration experiment. We observed decrease in initial and final aspirated lengths (L(0) and L(s) respectively) of ECs after 8 hours cyclic loading. Results also showed that L(0) and L(s) after 20% stretch were lower than those of 10% stretch (P<0.05). It was concluded that cells were remodeled after loading by alteration in visco-elastic behavior of cells. It has been shown that application of cyclic stretch leads to aggregation and reorientation of actin bundles inside the cell. The decrease in L(0) and also L(s) might be due to formation of stress fibers inside ECs after 8 hour cyclic stretch. Results of this study confirm that increased stretch amplitude and/or duration leads to less deformation and further stiffening of ECs. Results can be applied in production of engineered endothelial cells for tissue engineering and cell therapy.