Biomechanics of Repair in Invertebrates

Abstract

Repair is a ubiquitous process in nature, and it is one of the many features of biological materials that humans are constantly attempting to recreate. Though the process of repair has been studied in mammals, very little work has been done on other organisms, despite mammals representing just a minuscule percentage of global biodiversity. This thesis bridges some of these gaps in the knowledge, focusing of the repair process in two different organisms, the desert locust (Schistocerca gregaria) and the common limpet (Patella vulgata). For the locusts a link was drawn between age and repair capabilities, similar to that observed in mammals, finding that older insects are less capable of repair. Both young and old insects repair damage by the deposition of fresh material. Older cuticle was also found to have a decreased fracture toughness. This has implications for energy storage for jumping manoeuvres which was found to involve the deformation of the stiff tibial cuticle. This deformation causes microdamage to the cuticle, in addition to the viscoelastic changes in behaviour, and poses the potential risk of fatigue failure in cuticle. This damage is repaired in a week, similar to the repair of microcracks in bone. The fracture toughness of the limpet shells was similarly evaluated and found to be much higher than that of its main component, calcium carbonate. Several toughening mechanisms that help to achieve this were identified. The limpets were also found to be similarly susceptible to fatigue failure, though some remodelling process may be occurring. The limpets are also capable to repairing damage to their shells, and like the locusts they achieve this by depositing fresh material, though another unidentified mechanism is at work. Throughout this thesis comparisons were made to repair in mammalian bone. Bone has been very thoroughly studied and the mechanisms of repair are well understood. Several of the effects discussed in this thesis mirror effects observed in bone. Consequently, comparisons to bone are drawn to give greater context and enable discussion about the studies.