Mechanical Properties of the Beetle Elytron, a Biological Composite Material

Chemical and Petroleum Engineering, University of Kansas, Lawrence, Kansas 66045, USA.
Biomacromolecules (Impact Factor: 5.75). 02/2011; 12(2):321-35. DOI: 10.1021/bm1009156
Source: PubMed


We determined the relationship between composition and mechanical properties of elytra (modified forewings that are composed primarily of highly sclerotized dorsal and less sclerotized ventral cuticles) from the beetles Tribolium castaneum (red flour beetle) and Tenebrio molitor (yellow mealworm). Elytra of both species have similar mechanical properties at comparable stages of maturation (tanning). Shortly after adult eclosion, the elytron of Tenebrio is ductile and soft with a Young's modulus (E) of 44 ± 8 MPa, but it becomes brittle and stiff with an E of 2400 ± 1100 MPa when fully tanned. With increasing tanning, dynamic elastic moduli (E') increase nearly 20-fold, whereas the frequency dependence of E' diminishes. These results support the hypothesis that cuticle tanning involves cross-linking of components, while drying to minimize plasticization has a lesser impact on cuticular stiffening and frequency dependence. Suppression of the tanning enzymes laccase-2 (TcLac2) or aspartate 1-decarboxylase (TcADC) in Tribolium altered mechanical characteristics consistent with hypotheses that (1) ADC suppression favors formation of melanic pigment with a decrease in protein cross-linking and (2) Lac2 suppression reduces both cuticular pigmentation and protein cross-linking.

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Available from: Stevin H. Gehrke, Jan 24, 2015
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    • "Over a certain time-period when the possibility of wings being torn apart exists, testing a range of frequencies has an advantage, as high frequencies provide more data. In DMA analysis, Storage modulus (E′) provides a measurement of material stiffness [18], [35], [43], [44], [49]. Our results showed that E′ of the mutant is higher than that of the wild-type strain, indicating that the wings of the mutant are stiffer (Figure 8B). "
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