Tests conducted in collaboration with CiBER at U.C. Berkeley reveal the stress distribution within a gecko's toe (see images below). These are normal stress distributions measured on the same toe in different trials. The distributions are visibly nonuniform, showing that parts of the toe were not producing adhesion.
These measurements required a custom tactile sensor with high spatial resolution, which is capable of measuring both positive and negative normal forces. The sensor uses frustrated total internal reflection (FTIR) and a microtextured silicone film with small pyramidal bumps; the sensor converts an applied stress into an image that is recorded by a camera. Further details and results are reported in Eason et al., (2015) Stress distribution and contact area measurements of a gecko toe.
Markup makes downsized image show on page, but you get large image if you click it -MRC
|Stress distributions within a gecko's toe. |
Positive/yellow areas are under compression, negative/blue areas are under tension.
|Custom FTIR tactile sensor.|
|Stress distribution changing as the gecko's toe slips on the sensor (16 MB mov)||Gecko bringing its foot into contact (18 MB mov)||Changing contact area as the gecko's toes are pressed with a finger (6 MB mov)|