The Contribution of Crystallinity to Tissue-level Properties in Modern and Fossilized Bone
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1132-Z01-06
The Contribution of Crystallinity to Tissue-level Properties in Modern and Fossilized Bone Sara E. Olesiak1, Matthew Sponheimer2, Jaelyn J. Eberle3, and Virginia L. Ferguson1 1
Department of Mechanical Engineering, University of Colorado, Boulder, CO, 80309, USA Department of Anthropology, University of Colorado, Boulder, CO, 80309, USA 3 CU Museum and Department of Geological Sciences, University of Colorado, Boulder, CO, 80309, USA 2
ABSTRACT A range of mineral content values and organization of the collagen and mineral phases are possible contributors to the significant variance demonstrated within the nanomechanical behavior of mineralized tissues. A combined approach using nanoindentation, to assess nanomechanical behavior, and X-ray diffraction, for analysis of crystallinity and composition, were used to investigate a range of modern and fossilized bone samples. This work provides new insight into the functional role of organization and composition of the mineral phase within heterogeneous, mineralized materials of biological origin. While the predominant influence on nanomechanical behavior is made by mineral volume fraction, the crystallinity was shown to play a significant role in the nanomechanical behavior of modern and fossilized bone samples. The interplay between material structure and function will ultimately help to elucidate the relative contributions of various factors to nanomechanical behavior and lead to improved development of biomimetic materials. INTRODUCTION The mechanical response of mineralized tissues varies even at the nano scale, where largescale porosity and structural variation are not factors-yet other heterogeneities exist. While it is well known that mechanical properties generally increase with mineral volume fraction, a large range of modulus values are observed at a constant mineral content and thus mechanical properties cannot be explained by the mineral volume fraction and composites theory alone [1,2]. Recently a number of more advanced models have been applied to bone which consider hierarchy, porosity, and anisotropy [3] [4]. However, composite models of mineralized tissues are complicated by unknown physical characteristics of the constituent phases including the exact composition, size and shape of the mineral phase. These heterogeneities in mineral composition and crystallinity further contribute to the variations in mechanical properties of mineralized tissues. Bone has a heterogeneous mineral phase where a wide range of composition and crystallinity can be seen in healthy and diseased states. For example, in osteoporosis, an increase in crystallinity has been observed [5]along with compositional alterations as carbonate content increases and phosphate content decreases [6]. An understanding of the contribution of variations in crystallinity and composition to the nanomechanical properties of mineralized
tissues are vital to investigations of diseased states, structure-function relationships, and the development of mineralized replacement tissues. Bone
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