Fig. 6.

Microscale stress-strain behavior of zebrafish embryo yolk and uncured PDMS measured by active microrheology. (a) Sinusoidal oscillations of the trap position with increasing amplitudes of trap displacement increases applied force, stress, bead displacement and induced strain on the surrounding material. Probe displacements remain within the linear response regimes of both the detector and optical trapping potential but the material response is nonlinear. (b–e) Active microrheology measurements were conducted from 2 Hz – 12,8 kHz, with multiplexed frequencies at stress-strain amplitudes of 2 nm (blue), 5 nm (green) and 20 nm (red) trap displacement per frequency. (b, d) The elastic (G’, squares) and viscous (G”, triangles) components of the complex modulus are shown. (c, e) Corresponding complex viscosities η*. In both PDMS (b, c) and inside the yolks of living zebrafish embryos (d, e), the moduli show nonlinear viscoelasticity, increasing significantly with increasing stress-strain amplitude (p < 0.0001, two-way ANOVA).