Bioinspired Surgical Grasper Based on the Strong Wet Attachment of Tree Frog's Toe Pads

Abstract

Surgical grasper is one of the most common used tools in surgery. To effectively grasp soft slippery tissues, traditional surgical graspers are usually constructed with sharp teeth to deform tissue and form mechanical interlock between interfaces, which easily leads to strong tissue damages. Improvement of wet friction properties at the interface between the surgical grasper and soft tissue can greatly reduce the holding force required and the soft tissue damage. To design a surface with strong wet attachment performance, the wet attachment mechanisms of tree frog has been studied. Here we find that its toe pad is constructed with micropillar array, which mainly are hexagon. With liquid volume decreasing, the uniform liquid self-splitting effect has been observed on micropillar array surface, and the boundary friction appears on both tree frog's toe pad and bioinspired surface. This boundary friction mainly comes from the thin liquid film induced strong capillary force and leads to strong friction without any normal force. Besides, the anisotropic pillars and channels' distribution on toe pad leads to its directional dependent friction. By testing the friction of different pillar structure surfaces and traditional surgical grasper surfaces with macroscale teeth, the hexagonal pillar pattern exhibited improved wet frictional performance, which is appropriate for bioinspired surgical graspers. Finally, the soft tissue damage of these patterns was evaluated, and the effectiveness of biomimetic surface patterns when applied in surgical graspers is confirmed.