Osteoderms of Heloderma suspectum - A new nano-micro hierarchical biomineralized structure in vertebrates

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Author:Alexander Kirby1Collaborators:Michael Jossi1 Mehran Moazen2, Susan Evans3, Sergio Bertazzo11Department of Medical Physics & Biomedical Engineering, University College London, London WC1E 6BT, UK2Department of Mechanical Engineering, University College London, Torrington Place, London WC1E 7JE, UK 3Department of Cell & Developmental Biology, University College London, Gower Street, London WC1E 6BT, UKSummary:Helodermatidae is a family of venomous lizards that has evolved osteoderms within the skin. Since they were first reported, osteoderms have generally been described as bone or bone-like structures, and this concept has never been thoroughly challenged. In this project, the nano/micro characteristics of the osteoderms of Heloderma suspectum (Gila monster) are evaluated and compared to bone and tooth samples from the same animal. This characterization study is to be done using advanced physical-chemical analyses, such as electron microscopy associated with focused ion beam (FIB). At the micro scale, scanning electron micrograph results will prove or disprove that the osteoderm of the Gila monster can be divided into three regions: a highly mineralised dense material present in the upper region of the osteoderm; a bone-like material that runs through the osteoderm, apparently surrounding vasculature; and a mineralised region, with collagen fibers of approximately 10 microns of diameter organized in a three-dimensional mesh. At the nano scale, transmission electron micrographs of samples prepared by FIB will prove or disprove the hypothesis that each of the three different regions is unique, presenting different nanostructures and different crystallinity, as demonstrated by x-ray diffractometry. We also hypothesise that comparison with samples of bone and teeth taken from the same animal reveal that the osteoderm is indeed a unique mineralised tissue and not a simple bone-like tissue. These results then may prove an indication that in vertebrates, natural non-pathological hard tissues are more diverse than suspected, suggesting the existence of completely novel cellular and biochemical biomineralization systems. Further preliminary results indicate that the three structures described here for the Gila monster are the fundamental components of osteoderms in lizards, with variations in the shape and proportion of these three structures between species. Finally, beyond the biological, evolutionary and ecological significance of a new hard tissue discovered in vertebrates, the hitherto unknown nano/micro structures described here may potentially prove valuable in future translational applications, including the creation of biomimetic and bioinspired materials with special properties. For these reasons, this study is well aligned to the EPSRC research area of biomaterials and the strategies/grand challenges of developing future therapies, frontiers of physical intervention and advanced materials.The authors declare that no ethical approval was required for this study.