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Research Papers

Mechanics of Cell Mechanosensing on Patterned Substrate

[+] Author and Article Information
Chenglin Liu, Shijie He, Xiaojun Li

Biomechanics and Biomaterials Laboratory,
School of Aerospace Engineering,
Beijing Institute of Technology,
Beijing 100081, China

Bo Huo

Biomechanics and Biomaterials Laboratory,
School of Aerospace Engineering,
Beijing Institute of Technology,
No. 5 South Zhongguancun Street,
Beijing 100081, China
e-mail: huobo@bit.edu.cn

Baohua Ji

Biomechanics and Biomaterials Laboratory,
School of Aerospace Engineering,
Beijing Institute of Technology,
No. 5 South Zhongguancun Street,
Beijing 100081, China
e-mail: bhji@bit.edu.cn

1Corresponding authors.

Contributed by the Applied Mechanics Division of ASME for publication in the JOURNAL OF APPLIED MECHANICS. Manuscript received January 26, 2016; final manuscript received March 3, 2016; published online March 21, 2016. Editor: Yonggang Huang.

J. Appl. Mech 83(5), 051014 (Mar 21, 2016) (8 pages) Paper No: JAM-16-1052; doi: 10.1115/1.4032907 History: Received January 26, 2016; Revised March 03, 2016

It has been recognized that cells are able to actively sense and respond to the mechanical signals through an orchestration of many subcellular processes, such as cytoskeleton remodeling, nucleus reorientation, and polarization. However, the underlying mechanisms that regulate these behaviors are largely elusive; in particular, the quantitative understanding of these mechanical responses is lacking. In this study, combining experimental measurement and theoretical modeling, we studied the effects of rigidity and pattern geometry of substrate on collective cell behaviors. We showed that the mechanical force took pivotal roles in regulating the alignment and polarization of cells and subcellular structures. The cell, cytoskeleton, and nucleus preferred to align and polarize along the direction of maximum principal stress in cell monolayer, and the driving force is the in-plane maximum shear stress. The higher the maximum shear stress, the more the cells and their subcellular structures preferred to align and polarize along the direction of maximum principal stress. In addition, we proved that in response to the change of in-plane shear stresses, the actin cytoskeleton is more sensitive than the nucleus. This work provides important insights into the mechanisms of cellular and subcellular responses to mechanical signals. And it also suggests that the mechanical force does matter in cell behaviors, and quantitative studies through mechanical modeling are indispensable in biomedical and tissue engineering applications.

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Figures

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Fig. 1

The schematic illustration of cell traction measurement. (a) Upper: the cells adhering on the gel substrate; lower: the cells treated with trypsin for removing off from the gel. (b) Upper: the fluorescence image of gel surface with cells; lower: the fluorescence image of gel surface without cells for measuring the substrate deformation.

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Fig. 2

Free-body diagram of the element in cell layer. (a) The cell layer restrained by ringlike pattern substrate. (b) The top view of the free-body diagram of the element. (c) The side view of the free-body diagram of the element.

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Fig. 6

In-plane stresses in the cell layer. (a) Color map of predictions of in-plane maximum shear stress; (b) vectorial representation of predictions of the in-plane maximum principal stress; (c) the predictions of the in-plane maximum shear stress for two different substrate stiffnesses; (d) and (g) color map of the measured in-plane maximum shear stress on the 30 kPa gel (d) and 10 kPa gel (g); (e) and (h) the vectorial representation of the measured maximum principal stress on the 30 kPa gel (e) and 10 kPa gel (h); and (f) and (i) the measured in-plane maximum shear stress as function of the distance to the ring center on the 30 kPa gel (f) and 10 kPa gel (i). Scale bar: 50 μm.

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Fig. 5

Nucleus alignment and polarization on the ringlike patterned substrate. (a) Nucleus fluorescence image on 60 kPa gel; (b) nucleus fluorescence image on 10 kPa gel. (c) Nucleus orientation angle versus the radial position; (d) nucleus aspect ratio versus the radial position. Scale bar: 50 μm.

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Fig. 4

Actin distribution on the ringlike patterned substrate. (a) F-actin fluorescence image on 60 kPa gel; a zoom-in image illustrating how orientationj works. The yellow dotted ellipse shows the region of interest. The angle ϕ is defined as the angle between the major axis of the red ellipse and the horizontal direction, given by Eq. (A3) in the Appendix. And the angle θbetween the major axis of the red solid ellipse and the circumferential direction of the ring pattern can be calculated when ϕ is obtained. (b) F-actin fluorescence image on 10 kPa gel. (c) Actin orientation angle versus the radial position; (d) actin coherency versus the radial position. Scale bar: 50 μm. #:60 kPa versus 10 kPa, p < 0.05.

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Fig. 3

Cell alignment and polarization on the ring patterned substrate. (a) A quarter of phase contrast images of cell morphology on 60 kPa and 10 kPa PAA gel substrate with ring pattern (scale bar: 50 μm); (b) polar plot of cell angle distribution with respect to the circumferential angle; and (c) the mean cell angle as function of the distance to the ring center for two different stiffnesses. (d) The mean aspect ratio of cells versus the distance to the center of the ring pattern of different stiffnesses. #: 60 kPa versus 10 kPa, p < 0.05.

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