Morphological and Viscoelastic Properties of the Cicada Tymbal

Abstract

This paper focusses on the morphological and viscoelastic properties of the cicada tymbal from the species Dundubia rufivena. Morphological details were determined by scanning electron and fluorescence microscopy, while the viscoelastic properties were determined by dynamic mechanical thermal analysis, and further supported by differential scanning calorimetry. We find that water evaporation from the tymbal begins at 71.1 °C and the glass transition for the tymbal, which is a chitin–resilin composite, is on average 150 °C, though there is considerable heterogeneity in the material of the tymbal, as indicated by the half height peak width of the tymbal (35.3 °C) and the shoulder peak indicative of a second phase and hence glass transition at on average, 168 °C. This second phase is assumed to reflect the effects of large-scale molecular pinning and restructuring at resilin–chitin interfaces (possibly via specific binding domains). In addition, we elucidate that the predominantly resilin regions of the tymbal of Dundubia rufivena is reinforced by a polygonal mesh of chitin, a morphological feature that has not been described in any previous research on the cicada tymbal. We provide evidence for nonlinear elasticity in the tymbal by comparing the storage modulus of the tymbal at different frequencies and loading amplitudes.