A simple, high-resolution, non-destructive method for determining the spatial gradient of the elastic modulus of insect cuticle

Abstract

Nature has evolved structures with high load-carrying capacity and long-term durability. The principles underlying the functionality of such structures, if studied systematically, can inspire the design of more efficient engineering systems. An important step in this process is to characterize the material properties of the structure under investigation. However, direct mechanical measurements on small complex-shaped biological samples involve numerous technical challenges. To overcome these challenges, we developed a method for estimation of the elastic modulus of insect cuticle, the second most abundant biological composite in nature, through simple light microscopy. In brief, we established a quantitative link between the autofluorescence of different constituent materials of insect cuticle, and the resulting mechanical properties. This approach was verified using data on cuticular structures of three different insect species. The method presented in this study allows three-dimensional visualisation of the elastic modulus, which is impossible with any other available technique. This is especially important for precise finite-element modelling of cuticle, which is known to have spatially graded properties. Considering the simplicity, ease of implementation and high-resolution of the results, our method is a crucial step towards a better understanding of material-function relationships in insect cuticle, and can potentially be adapted for other graded biological materials.

Resilin Distribution and Sexual Dimorphism in the Midge Antenna and Their Influence on Frequency Sensitivity

“…CLSM furthermore has the advantage of allowing the imaging of whole structures with no loss of depth resolution, at higher resolutions than conventional light microscopy. In addition to this structural observation, finite element modelling (FEM) of the mechanical behaviour of the antennae with an elasticity distribution in accordance to the observed CLSM data (following the method of [24], see also [16]) shows the potential effect of element position on the mechanical sensitivity. Finally, we discuss the impact of sexual dimorphism of structures and material composition patterns on resonant tuning and its diversity among species in relation to their mating biology.…”

NEXAFS imaging to characterize the physio-chemical composition of cuticle from African Flower Scarab Eudicella gralli

“…This approach typically provides little information about spatial organization of this material and is not surface-specific. Organismal biology, on the other hand, uses microscopy imaging techniques, such as fluorescence light microscopy 3 , confocal laser scanning microscopy 4 and electron microscopy 5,6 in combination with mechanical and physical studies 7–11 , to capture information about the cuticle structure, its chemical composition at the microscale, and its properties in detail. However, since these methods are missing the chemical sensitivity and sub-nanoscale resolution, the use of other methods will be required.…”

Penetration mechanics of elongated female and male genitalia of earwigs

“…Bending stiffness is defined as the product of Young's modulus ( E ) and the second moment of area ( I ). Bending stiffness of the virga and spermatheca was estimated using the calculated second moment of area based on either SEM or CLSM images using the BoneJ plugin 27 for Fiji and the estimated Young's modulus based on the CLSM images using the program developed by Eshghi et al 28 .…”