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Session Schedule & Abstracts




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Sunday 3rd July, 2016

MAT2
Symposium: Interdisciplinary and evolutionary approaches to vertebrate biological materials 2

Room: Salon B   11:30 am–1:00 pm

Moderator(s): M. Dean, A. J. Crosby, D. Irschick, & L. Li
MAT2-1  11:30 am  Material perspectives on the evolution of bone across fishes and tetrapods. Kawano S*, National Institute for Mathematical and Biological Synthesis; Shahar R, Hebrew University of Jerusalem   skawano@nimbios.org
Abstract: Bones are an iconic feature of vertebrates and form a load-bearing skeleton that supports, protects, and allows movement of the body. The osteocytes, bone cells entombed within the bone matrix, are thought to orchestrate bone building and repair as well as the ability to respond to changing loads, yet these hypotheses have primarily resulted from observations made in amniotes. Studies of a wider array of vertebrates have revealed new dimensions in bone biology. Fish bones are particularly enigmatic because while sharing many similarities with mammalian bones, they also have some remarkably different features. In particular, most extant fishes have skeletons composed entirely of anosteocytic bone (i.e. complete lack of osteocytes). While the existence of anosteocytic fish bones has been known for over 100 years, studies on the functional consequences of anosteocytic bone have only recently gained momentum through the integration of cutting-edge techniques in engineering and biomedical imaging to biomaterials. These studies have demonstrated that fish bones exhibit various unique traits, including being less stiff but considerably tougher than mammalian bones. Yet another example is the osteocytic bone of amphibians, whose mechanical properties can vary with the locomotor capabilities of the animal. Evaluations of salamanders indicated that loading mechanics during terrestrial locomotion differ between the forelimbs and hind limbs, likely resulting from the different functions of these structures. These examples contribute novel perspectives to our understanding of the diverse form-function relationships of bones across non-amniote vertebrates. Given that many fishes and salamanders serve as modern analogs of early stem tetrapods, these data could catapult new advances in modeling how changes in the material properties and mechanical performance of bones across the fish-tetrapod transition may have contributed to functional innovations, such as the invasion of land.

MAT2-2  12:00 pm  Contractile and connective tissue interactions in skeletal muscles . Azizi E*, University of California, Irvine; Balaban JP, University of California, Irvine; Holt NC, University of California, Irvine   eazizi@uci.edu
Abstract: Many diverse systems overcome the power limitations of skeletal muscle by operating in series with biological springs like tendons. The power output of muscle-tendon units depends on 1) the capacity of muscles to generate mechanical work, 2) the ability of muscle to transfer mechanical work to tendons, and 3) the rate energy is released to the environment. Here we examine how the changes in the mechanical properties of intramuscular connective tissue structures (ECM) affect the generation of muscle work and how changes in the mechanical properties of tendons affect the storage of elastic energy. To produce work, muscle fibers actively shorten and, as muscle is isovolumetric, expand radially. This radial expansion is likely to be limited by the extracellular connective tissue scaffolding (ECM) in which the fibers are embedded. We predict that changes in the mechanical properties of the ECM will compromise muscle work by restricting radial expansion and thereby constraining a muscle's capacity to shorten. We use natural perturbation to the ECM (aging), enzymatic disruption of the ECM (collagenase), and physical constraints applied to muscles to show that limiting the radial expansion of a muscle reduces mechanical work output. We also predict that the amount of energy transferred from muscle to tendon requires a well tuned relationship between the force profile of a muscle and the stiffness of a tendon. We show that differences in tendon properties explain variation in muscle-tendon unit power output across three anuran species. Our work suggests that the muscle-tendon unit can be accurately characterized as a composite material where the tuned mechanical relationship between contractile and connective tissue structures define the upper limits of performance. Supported by NSF #1436476 and NIH #AR055295.

MAT2-3  12:30 pm  Evolution of crystal form and mineralization control in vertebrates. Omelon S.J.*, Department of Chemical and Biological Engineering, University of Ottawa; Habraken W.J., Max Planck Institute of Colloids and Interfaces   sidney.omelon@mpikg.mpg.de
Abstract: During the evolution of vertebrates, an intricate relationship between the organic building blocks of life (proteins, carbohydrates) and silicates, carbonate, and phosphate minerals has evolved, which generated fantastic, complex hierarchical structures with unprecedented material properties. Optimized mechanical strengths, stiffness, toughness, and chemical stability with minimal material density, achieved with controlled hierarchy over a range of length scales, are hallmarks of biological materials. In the study of biomineralization processes, shedding light on the formation of these complex, composite structures is similar to discovering the Holy Grail, and also opens new perspectives for the synthesis of high-performance materials, and treating skeletal diseases. In this talk we will present an overview of proposals for mineralization control in vertebrate skeletons. Phosphate biomineral (carbonated apatite) formation remains elusive, therefore different hypotheses for calcium phosphate biomineralization continue to be tested. We will not only describe and differentiate these proposed pathways, but will propose how a marriage of both theories fits best our current knowledge on how biological organisms may produce these mineralized structures.



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