Multi-Technique Investigation of a Biomimetic Insect Tarsal Adhesive Fluid

Abstract

There is substantial motivation to develop novel adhesives which take advantage of the superior adhesive strength and adaptability of many natural animal adhesives; however, the tools typically used to study these mechanisms are incapable of determining the precise interactions of molecules at an adhesive interface. In this study, a surface specific, order sensitive vibrational spectroscopy called sum frequency generation (SFG) is, for the first time, combined with multiple bulk characterization techniques to examine a novel, simple biomimetic adhesive fluid inspired by tarsal fluid of insects. Insects perform complex adhesive demands, including sticking, climbing vertically and running upside-down with little difficulty. Thus, we hypothesize that both bulk and surface specific properties of the fluid contribute to the success of this wet adhesive mechanism. SFG spectra of biomimetic emulsion exhibited similar hydrocarbon organization on hydrophobic and hydrophilic substrates to natural beetle fluid previously studied with the same method. Bulk characterization techniques indicated that the emulsion had a shear-thinning profile with the ability to enhance traction forces during climbing and low surface tension ideal for surface wetting on the majority of natural surfaces. Multi-technique comparisons between emulsion and pure squalane revealed that a hydrocarbon only based fluid could not replicate the traction promoting properties of the emulsion. We conclude that the insect tarsal fluid adhesive mechanism relies upon contributions from both surface-specific properties optimizing traction force and bulk properties promoting rapid surface wetting and maintaining pull-off force for fast detachment.

Characterization of Morphologically Distinct Components in the Tarsal Secretion of Medauroidea extradentata (Phasmatodea) Using Cryo-Scanning Electron Microscopy

“…The complexity of biological tarsal fluid makes it difficult to reproduce the properties of this secretion using artificial-hydrocarbon-based components because the artificial fluid only mimics a part of this complex mixture, which might be surface-specific. Additionally, the mimicking quality of the other physical properties of natural secretions in biomimetic adhesive fluids remains unknown [ 70 ].…”

Bio-inspired materials to control and minimise insect attachment

“…Experimental evidence showing the non-Newtonian nature of adhesive fluid has only recently been confirmed [105]. Current tribological models revealed that both the interfacial interactions between the fluid and substrate as well as the chemistry of the bulk play an equally important role for establishing shear-thinning properties [105,291]. Therefore, further nano-tribological investigations are needed to gain additional insights into the origin of the observed friction forces of various insect species.…”