Movie 5.

Representative examples of raw imaging data of the probe tip in hydrogel samples. Probe force constant k = 0.2 N m^-1, set to 10 V and with a sinewave frequency of 0.5 Hz, at an insertion depth of 230 μm. While the motor and probe holder move the same way in each sample, the probe movement can be seen to decrease as the stiffness increases. In very stiff samples, the probe is locally “stuck” and rotates around the half insertion point, resulting in the probe tip moving in an opposite direction to the motor (e.g., 3130 Pa and 5220 Pa). Timestamp in ss:ms.