Cells Under Stress: An Inertial-Shear Microfluidic Determination of Cell Behavior

Abstract

The deformability of a cell is the direct result of a complex interplay between the different constituent elements at the subcellular level, coupling a wide range of mechanical responses at different length scales. Changes to the structure of these components can also alter cell phenotype, which points to the critical importance of cell mechanoresponse for diagnostic applications. The response to mechanical stress depends strongly on the forces experienced by the cell. Here, we use cell deformability in both shear-dominant and inertia-dominant microfluidic flow regimes to probe different aspects of the cell structure. In the inertial regime, we follow cellular response from (visco-)elastic through plastic deformation to cell structural failure and show a significant drop in cell viability for shear stresses >11.8 kN/m 2 . Comparatively, a shear-dominant regime requires lower applied stresses to achieve higher cell strains. From this regime, deformation traces as a function of time contain a rich source of information including maximal strain, elastic modulus, and cell relaxation times and thus provide a number of markers for distinguishing cell types and potential disease progression. These results emphasize the benefit of multiple parameter determination for improving detection and will ultimately lead to improved accuracy for diagnosis. We present results for leukemia cells (HL60) as a model circulatory cell as well as for a colorectal cancer cell line, SW480, derived from primary adenocarcinoma (Dukes stage B). SW480 were also treated with the actin-disrupting drug latrunculin A to test the sensitivity of flow regimes to the cytoskeleton. We show that the shear regime is more sensitive to cytoskeletal changes and that large strains in the inertial regime cannot resolve changes to the actin cytoskeleton.

Physical Biomarkers of Disease Progression: On-Chip Monitoring of Changes in Mechanobiology of Colorectal Cancer Cells

“…, which was identified as the yield stress of the cells and is associated to cytoskeletal breakdown 32 Figure S1 shows the unnormalized data, DI as a function of Q, for the three cell lines in both shear and inertia-dominant regimes.…”

“…Figure S2 shows the velocity profiles calculated along the central axis of the extensional flow junction, that were fitted with a sine function and www.nature.com/scientificreports www.nature.com/scientificreports/ used to fit the Kelvin-Voigt model to the deformation trace (shown in red in Figure S2). As a comparison, control data from the averaged deformation trace of N = 50 HL60 cells is also included in Table 1 from Armistead et al (2019) 32 .…”

“…We have previously shown that a low-strain and shear dominant regime is most sensitive to cytoskeletal changes 32 . Thus, to study mechanical changes in our CRC model system we performed deformation tracking and multiparameter analysis of SW480, HT29 and SW620 deforming at Q = 5 µl/min, in the shear regime.…”

Elongation Index as a Sensitive Measure of Cell Deformation in High-Throughput Microfluidic Systems

“…Cross-slot microfluidic deformability cytometry (mDC) is a promising high-throughput approach for mechanotypic screening of living cells, but it is plagued with measurement errors associated with cell offset from the flow centerline (24,37) and pressure or velocity fluctuations at the inlet channels. One of the ways to reduce offset errors is to eliminate the off-distance deformation index (DI) data (20,23), which can make mDC less powerful in assessing changes in cell mechanotype. We have demonstrated via predictive computational modeling that the mDC output can be sensitized to mechanical properties of the cells such as shear elasticity without removing viable off-distance data.…”

“…Simple analytical expressions 4 that relate the DI with channel geometry and cell's viscoelastic properties based on Maxwell and Kevin-Voigt models exist only for the cell moving along the flow centerline under low-velocity, Stokes flow conditions (21)(22)(23)(24). Commercial software packages (e.g., COMSOL Multiphysics ® ) that can only simulate flow but not cell deformation in a cross-slot channel have been employed to optimize the channel geometry for mDC (20,21,(25)(26)(27). This approach worked well for Re ≤ 10, but failed for higher Re.…”