Fatigue and repair mechanisms in insect exoskeletons

• Applicant: Professor Dr. Jan-Henning Dirks
• Subject Area: Systematics and Morphology (Zoology)
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 525144237

Insect cuticle is one of the most common and versatile biological materials. Like any other biological structure, cuticle exoskeletons are at constant risk of being damaged by their environment. So far, most studies on the biomechanics of insect cuticle have been measuring “static” material parameters, such as stiffness, strength, hardness and fracture toughness. However, during the lifetime of an insect, many parts of the exoskeleton experience high numbers of loading. Thus, these studies on cuticle presumably only tell a part of the biomechanics story. Surprisingly, in relation to its biological significance, only very little is known about the ability of cuticle exoskeletons to cope with cycling loading and in particular fatigue related stresses. Do cuticle exoskeleton body parts just “withstand” stresses experienced during the normal life cycle of an insect and/or are they able to selectively repair fatigue related damage? The biomechanics of fatigue and repair in insect cuticle exoskeletons are an almost unexplored scientific field with several open fundamental questions. To set a starting point and a base for future research we will be performing one of the first systematic scientific studies on the fatigue and repair mechanisms in insect exoskeletons. We will investigate a) whether different exoskeletal body part show different responses to fatigue b) whether usage of an exoskeleton body part correlate with the respective fatigue mechanism and c) how fatigue properties correlate with histological composition of cuticle. To investigate these open questions and our hypotheses, we will use a cross-disciplinary scientific approach, combining biology, materials sciences, and mechanical engineering. We will perform a comprehensive morphological characterization on representative body parts of selected biomechanical model organisms. To examine whether different exoskeletal body parts have different modes of fatigue, we will measure, characterize and compare the response to cyclic loading of the respective samples. In vivo biomechanical experiments on removed single body parts and in situ tests on attached body parts will allow us to investigate the possible role of microdamage and damage repair mechanisms in determining the fatigue properties of cuticle. To investigate the fundamental “proximate” mechanisms determining differences in fatigue response of cuticle body parts, we will then perform detailed histological characterisation of the respective body parts and correlate the ultrastructure and composition of the cuticle with the respective fatigue response. The results of our experiments will result in experimental data on how insect exoskeletons react to cyclic loading and allow us to gain first insight and explore fundamental biomechanical principles of insect exoskeleton fatigue and help us to understand some of the insects’ secret of evolutionary success.

• DFG Programme: Research Grants