Figure 1: Probing semi-isolated fiber with soft cantilever.

(A) Cell spread on an elevated S-shaped PDMS pattern. A thin cytoplasmic sheet is bridging the gap between two adhesive sides of the pattern (left side of the cell). (B) Phase contrast image of the cell after microsurgery: the fiber is isolated from the cytoplasm. (C) Time course of the deformation: δ_s is the imposed stage displacement (blue – top curve), δ_clv is the cantilever displacement (red – bottom curve), e is the transverse fiber displacement (see 1F), calculated as the difference between δ_s and δ_clv (black – middle curve). The two phases of deformation are called “STRETCHING PHASE” (constant stage velocity) and “RELAXATION PHASE” (zero stage velocity). (D) Snapshots of the experiment in the frame of reference of the substrate. The motion of the stage and cantilever correspond to the displacements represented in 1C. (I) The cantilever is placed between the fiber and the rest of the cell; (II) then the stage is moved, so that the cantilever pulls the fiber outward (stretching phase); (III) the stage is then kept still to let the fiber relax (relaxation phase) and finally (IV) the probe is retracted and the fiber recovers its initial straight configuration. The white dashed line represents the position of the cantilever at the end of stretching phase (II), to highlight the additional small deformation of the fiber in (III). (E) Cartoon of the experiment in the laboratory frame of reference. The adhesive pattern is shown in blue, the cross-section of the cantilever in red and the probed fiber in black. Displacements are slightly exaggerated. e^∗ corresponds to the transverse displacement at the end of the traction phase, e′ represents additional elongation during the relaxation phase. (F) Geometry of the system and parameter: a fiber of initial half-length d is pulled over a transverse distance e with a cantilever force F_clv. The resulting half-length of the elongated fiber is (δ: fiber elongation, θ: the projection angle on the initial fiber axis, resisting tension is ). For A, B and D, scale bar is 10 μm.