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Advanced Microfluidic Device Designed for Cyclic Compression of Single Adherent Cells - PubMed

  • ️Mon Jan 01 2018

Advanced Microfluidic Device Designed for Cyclic Compression of Single Adherent Cells

Kenneth K Y Ho et al. Front Bioeng Biotechnol. 2018.

Abstract

Cells in our body experience different types of stress including compression, tension, and shear. It has been shown that some cells experience permanent plastic deformation after a mechanical tensile load was removed. However, it was unclear whether cells are plastically deformed after repetitive compressive loading and unloading. There have been few tools available to exert cyclic compression at the single cell level. To address technical challenges found in a previous microfluidic compression device, we developed a new single-cell microfluidic compression device that combines an elastomeric membrane block geometry to ensure a flat contact surface and microcontact printing to confine cell spreading within cell trapping chambers. The design of the block geometry inside the compression chamber was optimized by using computational simulations. Additionally, we have implemented step-wise pneumatically controlled cell trapping to allow more compression chambers to be incorporated while minimizing mechanical perturbation on trapped cells. Using breast epithelial MCF10A cells stably expressing a fluorescent actin marker, we successfully demonstrated the new device design by separately trapping single cells in different chambers, confining cell spreading on microcontact printed islands, and applying cyclic planar compression onto single cells. We found that there is no permanent deformation after a 0.5 Hz cyclic compressive load for 6 min was removed. Overall, the development of the single-cell compression microfluidic device opens up new opportunities in mechanobiology and cell mechanics studies.

Keywords: cell mechanics; compression; mechanobiology; microcontact printing; microfluidics; single-cell analysis.

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Figures

Figure 1
Figure 1

Overview and design of the microfluidic device for single-cell compression. (A) The top view of overall design of the device. The flow layer is labeled in magenta, and the control layer consists of trapping control valves (blue) and compression control valve (orange). (B) The zoomed-in top view of the compression chamber (marked in A) and the meandering microfluidic channel in the device. The orange compression control valve is on top of the compression chamber in the flow layer. The purple rectangles are the designed block attached to the deflection membrane for compression. (C) Side view schematic of the compression chamber. A rectangular block and fibronectin island are unique features of this device. (D) The zoomed-in top view of the main meandering microfluidic channel (marked in A) and trapping control valve (blue). The inside two columns and outside two columns are controlled separately by two different trapping control valves. (E) A picture of the device. (F,G) Side view schematics of the device when the compression control valve is uncompressed (F) or compressed (G) on a cell spread on the fibronectin island.

Figure 2
Figure 2

Simulation and experimental results for designing and verifying the PDMS membrane block design of the device for cell compression. (A) A simplified model of membrane and block for simulation. Three geometric parameters were defined: compression chamber width (w), block thickness (hb) and membrane thickness (hm). (B) Displacement of the simplified membrane and block model at different values of geometric parameters. (C) Vertical displacement of the membrane and block at different horizontal positions across the compression chamber with different block thicknesses. (D) Displacement of the simulated result for the complete device model. (E) Membrane deflection of different compression chamber widths as a function of applied pressure. n = 3 for each chamber width. Error bar denotes the standard error of mean. (F) Reconstructed 3D and side view images of 80 μm chamber width at different compression control valve pressures. Scale bar = 40 μm.

Figure 3
Figure 3

Schematic of multi-column, separately-controlled cell trapping. (A) A schematic of a microfluidic channel with n individually controlled columns. Each column consists of two channels, so subscripts 2i and 2i-1 (with i = 1,2,3,…, n) address individual channels. Pressures (P), flow rates (Q), and resistances (R) of the main microfluidic channel and the small microchannel were denoted in blue and red and are shown in the figure as blue and red dotted lines, respectively. (B,C) A schematic of the same microfluidic channel when the n columns of microfluidic channel are (B) controlled altogether (i.e., all values are ON) or (C) separately controlled (i.e., valves 1 to i are OFF and valves i + 1 to n are ON). The consequential changes in fluid flow resistance and pressure difference across cells are shown.

Figure 4
Figure 4

Two-step, pneumatically controlled cell trapping. (A) Brightfield image of the compression chamber and fluorescence images of the 1 μm Y (yellow)-G (green) fluorescent beads when the trapping control valve was pressurized at different pressures. Scale bar = 60 μm. (B,C) Brightfield images of the compression chamber (B) and fluorescence images of the trapped eGFP expressing MCF-10A cells (C) when the trapping control valve was changed from before trapping (C, left) to after first trapping step (C, middle) and second trapping step (C, right). Scale bar = 200 μm.

Figure 5
Figure 5

Alignment of microcontact-printed fibronectin for the attachment and compression of cells. (A) Brightfield and fluorescence images of the device and fibronectin, respectively. Scale bar = 50 μm. (B) Zoomed-in brightfield and fluorescence image of the device and fibronectin, respectively (left). Fluorescence image of the MCF-10A cell, labeling the DNA (cyan) and actin (magenta) (right). Scale bar = 20 μm.

Figure 6
Figure 6

Cyclic deflection of the membrane and compression of cells. (A) Reconstructed side view images of a MCF-10A cell at different applied pressures to compression control valve. Cyan: DNA; Magenta: actin. Scale bar = 10 μm. (B) (Top) The applied cyclic pressure in the compression control valve over time at 0.25 Hz (left) and 0.5 Hz (right). (Bottom) The measured fluorescence intensity of the rhodamine succinimidyl dye at the middle of the compression chamber over time when the compression control valves were pressurized at the corresponding frequencies. (C) Fluorescence images of the compression chamber at different time points, as indicated in (B). Scale bar = 20 μm. (D) The normalized cell height before and 6 min after 6-min cyclic compression alternating between 10 and 15 psi at 0.5 Hz (n = 6). Error bar denotes the standard error of mean. No statistical significance by t-test.

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