Dynamic mechanical analysis reveals reversible thermal effects in insect tibial cuticle.

Abstract

The mechanical performance of insect cuticle arises from its composite structure of chitin fibres embedded in a protein-rich matrix. While chitin contributes to thermal resistance and structural integrity, the protein component is temperature-sensitive and modulates viscoelastic behaviour. Here, we investigated how thermal exposure affects the mechanical properties of tibial cuticle in Locusta migratoria, using dynamic mechanical analysis (DMA) across a temperature range (22-74 °C) and following prior heating to 60 °C or 70 °C. Both storage and loss moduli decreased significantly with increasing temperature by approx. 64 %, respectively 42 %, consistent with partially reversible thermal softening. After re-cooling, the loss modulus increased again to control levels, whereas the storage modulus remained significantly reduced. Tan δ increased significantly with increasing temperature by approx. 31 % and remained higher in pre-heated samples, reflecting a shift toward more compliant and dissipative behaviour. No significant differences were detected between the 60 °C and 70 °C treatments. These results suggest that thermal exposure induces reversible changes in matrix protein mobility and non-covalent interactions, affecting stiffness more strongly than damping. The cuticle thus exhibits partial recovery of mechanical function after heating, which may reflect an adaptive response to transient thermal stress.