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Title: Mechanical properties of the beetle elytron, a biological composite material

Author
item Lomakin, Joseph
item Huber, Patricia - University Of Kansas
item Eichler, Christian - University Of Kansas
item Arakane, Yasuyuki - Kansas State University
item Kramer, Karl - Retired Ars Employee
item Beeman, Richard
item Kanost, Michael - Kansas State University
item Gehrke, Stevin - University Of Kansas

Submitted to: Biomacromolecules
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/21/2010
Publication Date: 1/1/2011
Citation: Lomakin, J., Huber, P.A., Eichler, C., Arakane, Y., Kramer, K.J., Beeman, R.W., Kanost, M.R., Gehrke, S.H. 2011. Mechanical properties of the beetle elytron, a biological composite material. Biomacromolecules. 12(2):321-335. doi: http://dx.doi.org/10.1021/bm1009156.

Interpretive Summary: The exoskeleton, or cuticle, forms a protective outer covering or “skin” of insects, and is a potential model for next-generation plastics that would have increased biodegradability and environmental safety. In this work we have quantified the physical properties of the developing adult cuticle. We monitored the brittleness, elasticity and strength of cuticle of the new beetle wing covers as they harden and dry immediately after the insect sheds its old skin. Studies such as these will lead to better understanding of insect growth and development, better strategies for disrupting the associated genes for pest control, and new ideas for the design of next-generation biodegradable plastics.

Technical Abstract: We determined the relationship between composition and mechanical properties of elytral (modified forewing) cuticle of the beetles Tribolium castaneum and Tenebrio molitor. Elytra of both species have similar mechanical properties at comparable stages of maturation (tanning). Shortly after adult eclosion, elytra of Tenebrio were ductile and soft with a Young's modulus (E) of 44±8 MPa, but become brittle and stiff with an E of 2400±1100 MPa when fully tanned. With increasing tanning, dynamic elastic moduli (E’) increase nearly 20 times, while the frequency dependence of E' diminishes. This suggests that cuticle tanning involves cross-linking of components, as drying to minimize plasticization has a lesser impact on cuticular stiffening and frequency dependence. Suppression of the tanning enzymes laccase2 (TcLac2) or aspartate 1-decarboxylase (TcADC) in Tribolium altered mechanical characteristics consistent with hypotheses that ADC inhibition favors formation of melanic pigment with a decrease in protein cross-linking, whereas TcLac2 suppression inhibits both processes.