Figure 2.

Validation of cross-slot mechanical measurements with cross-linked dextran hydrogel particles. (A) Time-lapse of a Sephadex G200 cross-linked dextran particle stretching in extensional flow as it passes through the stagnation point region. The shear modulus is extracted from the observed deformation. Cross-slot dimensions are 400 μm wide and 200 μm deep. The strain rate is ξU/D ∼ 520 s⁻¹ at a 20 mL/h flow rate. Right: Overlay of the ellipses manually fitted to images of the dextran particle at the entrance of the cross-slot region and at the location closest to the stagnation point. The deformation was chosen to be an average case of all observed deformations. (B) Deformation of Sephadex G200 beads as a function of the applied stress. Suspending fluids with three viscosities were used, μ = 105 mPa·s, 179 mPa·s, and 201 mPa·s. A linear regression of ε = 5ξμU/(2GD) provides the shear modulus of G = 8.6 ± 0.5 kPa. Reported uncertainties of our measurements are the standard errors of the mean values of the population of dextran beads. (C) Micropipette aspiration of Sephadex G200 beads. The entry length, L, is normalized by the micropipette radius, R_p, and plotted as a function of the applied pressure, ΔP. Each color represents a different bead (n = 5 beads), and the shear modulus is inversely proportional to the slope. (D) Comparison of shear-modulus values obtained with our cross-slot measurements, our MPA measurements, and previously published values based on osmotic deswelling (43) and suspension rheology (44). To see this figure in color, go online.