Nanoscale in vivo evaluation of the stiffness of Drosophila melanogaster integument during development

Abstract

A quasistatic nanoindentation technique, enhanced by scanning probe microscopy, was used to measure cuticle stiffness of live Drosophila melanogaster during its larval, pupal, and early adult development in vivo. Stiffness was defined as the reduced elastic modulus (E(r)), which is a material property related to the elastic modulus. E(r) was measured at the local contact while indenting the live sample at a constant loading rate using a spherical tip. E(r) was derived from the resultant force-displacement curves. Insect cuticle exhibits viscoelastic behavior. Constant loading rate quasistatic measurements were used so that the effects of viscosity and contact force adhesion introduced systematic measurement effects. E(r) values were as follows: larvae, mean (SE), 0.39 (0.01) MPa; the puparium without evidence of adult structures 15.43 (1.78) MPa; and the adult, measured in the puparium at the completion of metamorphosis, 4.37 (0.31) MPa. Thus, as expected, the puparium and adult cuticle were very much stiffer than larval cuticle. Results also indicated stiffness variation that related to developmental events. This study has shown that this quasistatic nanoindentation-scanning probe microscopy approach is a suitable method for analyzing live biological samples.

Local mechanical properties of the head articulation cuticle in the beetlePachnoda marginata(Coleoptera, Scarabaeidae)

“…Residual deformation of the cuticle surface after indentation is similar to an elasticplastic contact, which is typical for most engineering materials (Bhushan and Li, 2003). The deviation of the residual imprint from the perfect pyramidal shape results from a visco-elastic relaxation, as is expected for soft biological materials (Wainright et al, 1976;Vincent, 1990;Kohane et al, 2003). This relaxation behaviour is especially evident on the lateral surfaces of the imprint, where the material almost goes back to its original condition ('cushion formation').…”

“…The results showed that the thickness of the cuticle and the development stage of the insect are important factors influencing cuticle stiffness (Kohane et al, 2003). The mean E r of 0.41·MPa, 15.43·MPa, and 4.37·MPa were determined by in vivo experiments for the cuticles of larvae, pupae and adult insects, respectively.…”

Exoskeletal chitin scales isometrically with body size in terrestrial insects

“…Cuticular elasticity can also differ among body parts within a single species, as has been observed in the differing elasticity of the locust hind tibia, forewing and pleural cuticle (Jensen and Weisfogh, 1962). Cuticular stiffness may also vary across developmental stages as has been found in Drosophila among larvae, pupae, and adults (Kohane et al, 2003). These differences in material properties are attributable to factors such as sclerotization, the relative amounts of chitin and protein, and the types of matrix proteins making up the cuticle (Hillerton and Vincent, 1979;Kramer et al, 1995;Andersen et al, 1996).…”

Scaling, dimensional analysis, and indentation measurements

“…The application areas include microelectronics, optoelectronics, coatings for low-emission window glasses, and tribological coatings [22][23][24][25][26][27][28]. Presently, there is also a growing interest in probing biological materials [29][30][31][32][33][34][35] and food products [36,37]. Instrumented indentation measurements have also been used in the study of the deformation and fracture of rocks for a better understanding of rock mechanics related to geological evolution of the planets [38,39].…”