A study on the microstructure and micromechanical properties of Drosophila larval cuticle using scanning probe microscopy and viscoelastic modeling.

Abstract

The Drosophila larval cuticle exhibits compliant yet resilient viscoelasticity, serving as a soft exoskeleton that enables effective locomotion while maintaining structural integrity. Investigating its microstructure and micromechanical properties not only advances our understanding of soft-bodied biomechanics but also guides the design of biomimetic materials and soft robotic systems. In this study, we employed scanning probe microscopy (SPM)-based stress relaxation tests to characterize viscoelastic properties across the denticle and smooth skin bands in three larval instars. Four viscoelastic models were evaluated, and the five-element Maxwell (MX5) model provided the best fit, enabling the extraction of mechanical parameters and plotting of relaxation modulus functions. Results showed that the larval instar stage had minimal influence on viscoelasticity, while the denticle and smooth skin bands exhibited distinct mechanical behaviors. Across all instars, the denticle bands showed higher moduli throughout the relaxation process, and notably, exhibited a greater degree and faster rate of relaxation compared to the smooth skin bands. These findings reveal region-specific viscoelastic adaptations that enable rapid stress dissipation while maintaining stiffness, supporting effective deformation during locomotion. This study provides essential quantitative foundations for bioinspired stretchable electronics, soft robotic materials, and broader understanding of soft exoskeleton mechanics.