Hybrid Surface Patterns Mimicking the Design of the Adhesive Toe Pad of Tree Frog

TL;DR

This paper presents a bioinspired fabrication method for hierarchical micropatterns mimicking tree frog toe pads, demonstrating enhanced adhesion and friction through anisotropic design and nanopillar integration.

Contribution

It introduces a novel fabrication technique for composite micropatterns inspired by tree frog toe pads, revealing improved adhesion and friction properties in wet environments.

Findings

Hierarchical design improves adhesion and friction.

Nanopillars alter stress distribution at contact interfaces.

Enhanced performance in wet conditions.

Abstract

Biological materials achieve directional reinforcement with oriented assemblies of anisotropic building blocks. One such example is the nanocomposite structure of keratinized epithelium on the toe pad of tree frogs, in which hexagonal arrays of (soft) epithelial cells are crossed by densely packed and oriented (hard) keratin nanofibrils. Here, a method is established to fabricate arrays of tree-frog-inspired composite micropatterns composed of polydimethylsiloxane (PDMS) micropillars embedded with polystyrene (PS) nanopillars. Adhesive and frictional studies of these synthetic materials reveal a benefit of the hierarchical and anisotropic design for both adhesion and friction, in particular, at high matrix-fiber interfacial strengths. The presence of PS nanopillars alters the stress distribution at the contact interface of micropillars and therefore enhances the adhesion and friction of the composite micropattern. The results suggest a design principle for bioinspired structural adhesives, especially for wet environments.