Timescale of k-fiber breakage under sustained force from microneedle, related to Fig. 4 . (A) Plot of the duration of manipulation for cells whose k-fibers broke or did not break under sustained applied force from the microneedle. The k-fibers broke when under force for slightly longer durations (plot shows mean ± SEM, P = 0.09, two-sided Mann–Whitney U test). (B and C) Additional examples of time-lapse images of k-fiber (GFP-tubulin, white) bending, lengthening, and breaking under sustained force. Insets with enhanced contrast show local changes to the structure of the deformed k-fiber near the area of high curvature next to the microneedle (Alexa 647, yellow). The break creates two fragments of the original k-fiber (purple arrowheads). Scale bar, 4 µm.