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Research Papers

A Device to Study the Effects of Stretch Gradients on Cell Behavior

[+] Author and Article Information
William J. Richardson, Michael R. Moreno, James E. Moore

Department of Biomedical Engineering,  Texas A&M University, 337 Zachry Engineering Center, 3120 TAMU, College Station, TX 77843

Richard P. Metz, Emily Wilson

 Department of Systems Biology and Translational Medicine, Texas A&M Health Science Center, 336 Reynolds Medical Building, College Station, TX 77843

J Biomech Eng 133(10), 101008 (Nov 01, 2011) (9 pages) doi:10.1115/1.4005251 History: Received June 15, 2011; Revised October 02, 2011; Published November 01, 2011; Online November 01, 2011

Mechanical forces are key regulators of cell function with varying loads capable of modulating behaviors such as alignment, migration, phenotype modulation, and others. Historically, cell-stretching experiments have employed mechanically simple environments (e.g., uniform uniaxial or equibiaxial stretches). However, stretch distributions in vivo can be highly non-uniform, particularly in cases of disease or subsequent to interventional treatments. Herein, we present a cell-stretching device capable of subjecting cells to controllable gradients in biaxial stretch via radial deformation of circular elastomeric membranes. By including either a defect or a rigid fixation at the center of the membrane, various gradients are generated. Capabilities of the device were quantified by tracking marked positions of the membrane while applying various loads, and experimental feasibility was assessed by conducting preliminary experiments with 3T3 fibroblasts and 10T1/2 cells subjected to 24 h of cyclic stretch. Quantitative real-time PCR was used to measure changes in mRNA expression of a profile of genes representing the major smooth muscle phenotypes. Genes associated with the contractile state were both upregulated (e.g., calponin) and downregulated (e.g., α-2-actin), and genes associated with the synthetic state were likewise both upregulated (e.g., SKI-like oncogene) and downregulated (e.g., collagen III). In addition, cells aligned with an orientation perpendicular to the maximal stretch direction. We have developed an in vitro cell culture device that can produce non-uniform stretch environments similar to in vivo mechanics. Cells stretched with this device showed alignment and altered mRNA expression indicative of phenotype modulation. Understanding these processes as they relate to in vivo pathologies could enable a more accurately targeted treatment to heal or inhibit disease, either through implantable device design or pharmaceutical approaches.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic of stretching device. A computer-controlled stepper motor drives radial deformation of a circular membrane via stretching over an indenter disk. The assembly can be mounted on an inverted microscope for imaging through a cover slip in the bottom of the box.

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Figure 2

Membrane deformation schematic. As the clamp ring is vertically displaced, the membrane is stretched over the stationary indenter disk. This action radially deforms the cell-seeded membrane while holding it at a constant focal plane for imaging.

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Figure 3

Device stretching capabilities. Stretch profiles for defect and fixation (both small and large) central boundary conditions. Membranes were deformed by vertically displacing the clamped outer circumference at levels ranging from 3.75–7.5 mm. Stretch ratios were calculated from measured positions of marked points and fit by solving the corresponding finite deformation problem using a Mooney-Rivlin strain energy function.

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Figure 4

Potential experimental stretching cases. Boxes highlight regions that span identical stretch magnitude ranges and anisotropy ratios, but different stretch gradients.

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Figure 5

3T3 fibroblast alignment in response to 24 h of cyclic stretch. Cells oriented perpendicular to their largest stretch component (circumferential stretch). Note that these images are not of identical cells but representative of the overall population. Scale bar is 50 μm.

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