Slow viscoelastic response of resilin

Abstract

The high importance of resilin in invertebrate biomechanics is widely known. It is generally assumed to be an almost perfect elastomer in different tissues. Whereas mechanical properties of resilin were previously determined mainly in tension, here we aimed at studying its mechanical properties in compression. Microindentation of resilin from the wing hinge of Locusta migratoria revealed the clear viscoelastic response of resilin: about a quarter of the mechanical response was assigned to a viscous component in our experiments. Mechanical properties were characterized using a generalized Maxwell model with two characteristic time constants, poroelasticity theory, and alternatively using a 1D model with just one characteristic time constant. Slow viscous responses with 1.7 and 16 s characteristic times were observed during indentation. These results demonstrate that the locust flight system is adapted to both fast and slow mechanical processes. The fast highly elastic process is related to the flight function and the slow viscoelastic process may be related to the wing folding.

Appendix

The springs’ stiffness distribution could be derived as follows: $P\left( K \right)\sim {{dy} \mathord{\left/ {\vphantom {{dy} {dK}}} \right. \kern-0pt} {dK}}$, $y={z_0}+R\sqrt {\left( {x - {x_0}} \right)} ,$ where x and y are horizontal and vertical co-ordinates of the substrate, z is a vertical co-ordinate of the indenting sphere with radius R, x₀ and z₀ are the vertical co-ordinates of the deepest position of the material and of the indenting sphere (Fig. 4). Following this line, after differentiating Eq. 3, equation shown in the legend to the Fig. 6 could be obtained.