Mechanical Characterization of Stick Insect Tarsal Attachment Fluid Using Atomic Force Microscopy (AFM)

Area of Science:

• Biophysics
• Materials Science
• Insect Physiology

Background:

• Insects utilize specialized tarsal pad fluids for attachment.
• Previous research explored fluid characteristics, but mechanical properties of smooth pad fluids remain understudied.

Purpose of the Study:

• To investigate the viscoelastic properties of adhesive pad fluid from the stick insect *Sungaya aeta*.
• To characterize the mechanical behavior of insect tarsal secretions.

Main Methods:

• Utilized stress-relaxation nanoindentation with atomic force microscopy (AFM) to measure viscoelastic properties.
• Applied Johnson-Kendall-Roberts (JKR) and generalized Maxwell models for data analysis.
• Employed white light interferometry (WLI) to determine droplet height.

Main Results:

• Identified three distinct droplet categories: "almost inviscid", "viscous", and "rigid".
• Observed that droplet properties are determined upon secretion and are stable over time.
• Demonstrated non-uniform composition across different droplet types based on mechanical properties.

Conclusions:

• The study reveals diverse mechanical properties of insect tarsal pad fluids.
• Findings contribute to understanding adaptive adhesion mechanisms in insects.
• Results may inform the development of novel soft adhesives and gripping technologies.