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Research Papers

A Shearing-Stretching Device That Can Apply Physiological Fluid Shear Stress and Cyclic Stretch Concurrently to Endothelial Cells

[+] Author and Article Information
Daphne Meza, Louie Abejar, David A. Rubenstein

Department of Biomedical Engineering,
Stony Brook University,
Stony Brook, NY 11794

Wei Yin

Department of Biomedical Engineering,
Stony Brook University,
Stony Brook, NY 11794
e-mail: wei.yin@stonybrook.edu

1Corresponding author.

Manuscript received June 12, 2015; final manuscript received January 10, 2016; published online February 5, 2016. Assoc. Editor: Kristen Billiar.

J Biomech Eng 138(3), 031007 (Feb 05, 2016) (8 pages) Paper No: BIO-15-1297; doi: 10.1115/1.4032550 History: Received June 12, 2015; Revised January 10, 2016

Endothelial cell (EC) morphology and functions can be highly impacted by the mechanical stresses that the cells experience in vivo. In most areas in the vasculature, ECs are continuously exposed to unsteady blood flow-induced shear stress and vasodilation-contraction-induced tensile stress/strain simultaneously. Investigations on how ECs respond to combined shear stress and tensile strain will help us to better understand how an altered mechanical environment affects EC mechanotransduction, dysfunction, and associated cardiovascular disease development. In the present study, a programmable shearing and stretching device that can apply dynamic fluid shear stress and cyclic tensile strain simultaneously to cultured ECs was developed. Flow and stress/strain conditions in the device were simulated using a fluid structure interaction (FSI) model. To characterize the performance of this device and the effect of combined shear stress–tensile strain on EC morphology, human coronary artery ECs (HCAECs) were exposed to concurrent shear stress and cyclic tensile strain in the device. Changes in EC morphology were evaluated through cell elongation, cell alignment, and cell junctional actin accumulation. Results obtained from the numerical simulation indicated that in the “in-plane” area of the device, both fluid shear stress and biaxial tensile strain were uniform. Results obtained from the in vitro experiments demonstrated that shear stress, alone or combined with cyclic tensile strain, induced significant cell elongation. While biaxial tensile strain alone did not induce any appreciable change in EC elongation. Fluid shear stress and cyclic tensile strain had different effects on EC actin filament alignment and accumulation. By combining various fluid shear stress and cyclic tensile strain conditions, this device can provide a physiologically relevant mechanical environment to study EC responses to physiological and pathological mechanical stimulation.

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Figures

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Fig. 2

A constant angular velocity (18 rad/s) was used as the velocity input of the cone, and a cyclic vacuum pressure (magnitude at 30 kPa, frequency at 1.1 Hz) was used as the transient pressure input on the flexible membrane

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Fig. 1

The schematic drawing of the shearing and stretching device. (a) The housing for a cell culture plate, (b) the six-well cell culture plate with flexible membranes, (c) shearing cones, (d) the piston pump, and (e) enlarged view of the flexible membrane and the supporting plate.

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Fig. 3

(a) Velocity (m/s) vectors of the fluid phase as the vacuum pressure changed between 0 and 30 kPa in one stretching cycle. Simultaneously, the cone was rotating at a constant angular velocity of 18 rad/s. (b) Corresponding shear stress (Pa) distribution in the flow field when both the cone and the membrane were moving.

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Fig. 4

(a) Nodal displacement along the radial direction in the in-plane area of the membrane at the maximum deformation (t = 0.6 s). (b) Circumferential and radial strain of a randomly chosen node (6 mm from the center of the membrane) change as a function of time during one stretching cycle.

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Fig. 5

Measured circumferential and radial strain. (a) Radial strain did not vary significantly with angle (P > 0.3); (b) circumferential strain did not vary significantly with radial distance (P > 0.1). The circumferential and radial strains do not differ (P > 0.1), indicating strain field uniformity.

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Fig. 6

Representative images of ECs following shear stress and/or tensile strain treatment. White arrows indicate flow direction and red arrows indicate the directions of tensile strain. Scale bars represent 25 μm.

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Fig. 7

(a) Cell elongation and (b) nucleus elongation after HCAEC were treated with shear stress and/or cyclic tensile strain. Data are presented as mean + standard deviation (n = 24). *indicates significant difference (P < 0.05).

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Fig. 8

Actin alignment was quantified using FFT. Significant difference was detected between ECs that were treated with shear stress alone, and those treated with tensile strain alone (P < 0.05, n = 12–19). Data are presented as mean + standard deviation.

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Fig. 9

Actin accumulation along EC boundaries. Shear stress, alone or combined with tensile strain, induced significant increase in actin accumulation along cell boundaries (P < 0.05, n = 31–93). Biaxial tensile strain alone did not induce any changes in actin accumulation at cell junctions. Data are presented as mean + standard deviation.

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