Generating Secure and Gentle Grip on Soft Substrates

Generation of grip on soft tissue in the surgical field is most commonly done with forceps that generate friction grip, that is, the translation of normal (pinch) forces into shear forces. Errors made with these surgical grippers are often force-related: applying too low pinch forces results in slipping of the tissue out of the gripper, and too high pinch forces may lead to tissue damage. One possible solution for generating tissue grip that is secure yet gentle is the adhesive grip. In this case, contact between tissue and gripper is maintained by attracting gripper-tissue interactions, and gripping strength does not depend on the applied pinch forces. Inspiration for the design of such a gripper can be derived from the tree frog, an animal that uses adhesive grip to grip on a range of substrates in its habitat. The main aim of this thesis is to translate grip-generating principles used by tree frogs into designs of artificial adhesives that can generate firm yet gentle grip on soft substrates. The designs of the artificial adhesives in this thesis are inspired by two important characteristics of the tree frog’s attachment apparatus: the hierarchical surface pattern on the tree-frog toe-pad and reinforcing fibrillar structures located inside the pad. Specifically, the aim of this thesis is to mimic function rather than form, and focuses on mechanisms underlying the tree-frog attachment apparatus to satisfy two main requirements for strong grip: (1) contact formation and (2) preservation of the formed contact.