Fig. 5. Mapping stiffness of primary cilia. (A) Principle of non-contact measurement of stiffness using SICM. Displacement between 0.3 % current drop (typical topography setpoint) and 1% current drop is measured to obtain the stiffness. As illustrated on the right, the measurement is likely to cause compression in extra-ciliary membrane as well as at the base of cilia, but more likely to cause pivoting or bending of the whole cilium when targeting the tip of cilia. (B) Comparison of mean stiffness of cilia base and tip versus extra-ciliary membrane (ExC) (n = 7). Example of simultaneously obtained height-coded topography image of a live primary cilium (C) and its stiffness map (D). The dotted circles mark the membrane regions of cilium tip (white), cilium base (green) and extra-ciliary membrane (red). *p<0.05, **p<0.01