The physical origins of transit time measurements for rapid, single cell mechanotyping

Abstract

The mechanical phenotype or 'mechanotype' of cells is emerging as a potential biomarker for cell types ranging from pluripotent stem cells to cancer cells. Using a microfluidic device, cell mechanotype can be rapidly analyzed by measuring the time required for cells to deform as they flow through constricted channels. While cells typically exhibit deformation timescales, or transit times, on the order of milliseconds to tens of seconds, transit times can span several orders of magnitude and vary from day to day within a population of single cells; this makes it challenging to characterize different cell samples based on transit time data. Here we investigate how variability in transit time measurements depends on both experimental factors and heterogeneity in physical properties across a population of single cells. We find that simultaneous transit events that occur across neighboring constrictions can alter transit time, but only significantly when more than 65% of channels in the parallel array are occluded. Variability in transit time measurements is also affected by the age of the device following plasma treatment, which could be attributed to changes in channel surface properties. We additionally investigate the role of variability in cell physical properties. Transit time depends on cell size; by binning transit time data for cells of similar diameters, we reduce measurement variability by 20%. To gain further insight into the effects of cell-to-cell differences in physical properties, we fabricate a panel of gel particles and oil droplets with tunable mechanical properties. We demonstrate that particles with homogeneous composition exhibit a marked reduction in transit time variability, suggesting that the width of transit time distributions reflects the degree of heterogeneity in subcellular structure and mechanical properties within a cell population. Our results also provide fundamental insight into the physical underpinnings of transit measurements: transit time depends strongly on particle elastic modulus, and weakly on viscosity and surface tension. Based on our findings, we present a comprehensive methodology for designing, analyzing, and reducing variability in transit time measurements; this should facilitate broader implementation of transit experiments for rapid mechanical phenotyping in basic research and clinical settings.

Cancer cells become less deformable and more invasive with activation of β-adrenergic signaling

“…The retention of each sample, in which the final mass is expressed as a percentage of the initial mass of loaded cell suspension, reflects the number of cells that occlude the membrane pores: a higher retention indicates a larger volume of cell suspension retained in the top well, which results from a larger number of occluded pores. The probability of pore occlusion depends on the external applied pressure, cell-to-pore size ratio and cell-surface interactions, as well as the mechanical properties of cells, such as their elastic and viscous moduli (Nyberg et al, 2016;Qi et al, 2015). At a constant applied pressure and pore size, cell deformability is a major contributor to the transit of cells through pores (Shaw Bagnall et al, 2015), and thus the retention that we measure (Qi et al, 2015).…”

High-throughput physical phenotyping of cell differentiation

“…Cell physical properties, including the shape, size and resistance of cells to an applied load, stem from other structural and molecular cell properties in a complex manner that is not easily discerned [1][2][3][4] . Compared to the conventional molecular biomarkers, these physical properties integrate many molecular changes.…”

Impact of Channel Geometry on the Discrimination of Mechanically Impaired Red Blood Cells in Passive Microfluidics

“…Finally, we investigated cells relaxation time τ as a biomarker. It has been shown in literature [5] that 1/τ increases linearly with the cell velocity. Figure 3b represents the slopes α of 1/τ = f(V3) curves (see insert) for both populations flowing in the two geometries.…”

“…Various techniques have been reported in literature to evaluate RBC mechanical properties through the measurement of different parameters, i.e., the cortical tension [1], flowing speed through a network of constrictions [2], the time necessary to reach a steady state starting from rest [3], as well as their maximal deformability and their shape relaxation time (τ) [4]. Passive microfluidic techniques have emerged as powerful, label free, high throughput methods to assay those mechanical characteristics, using specific geometries [5]. In the present work, we used a passive microfluidic approach to differentiate mechanically impaired from healthy RBCs.…”