Effect of Water on Mechanical Properties of Mineralized Tissue Composites
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Effect of Water on Mechanical Properties of Mineralized Tissue Composites Amanpreet K. Bembey1, Michelle L, Oyen1, Virginia L. Ferguson2, Andrew J. Bushby1, and Alan Boyde3 1 Department of Materials, Queen Mary, University of London, Mile End Road, London, E1 4NS, United Kingdom 2 Department of Mechanical Engineering, University of Colorado, Boulder, CO, 80309 3 Oral Growth and Development, Queen Mary, University of London, London, E1 1BB, United Kingdom ABSTRACT In the current study, the effects of polar solvents on tissue volume and mechanical properties are considered. Area shrinkage measurements are conducted for mineralized bone tissue samples soaked in polar solvents. Area shrinkage is used to calculate approximate linear and volume shrinkage. Results are compared with viscoelastic mechanical parameters for bone in the same solvents (as measured previously) and with both shrinkage measurements and mechanical data for nonmineralized tissues, as taken from the existing literature. As expected, the shrinkage of mineralized tissues is minimal when compared with shrinkage of nonmineralized tissues immersed in the same polar solvents. The mechanical changes in bone are also substantially less than in nonmineralized tissues. The largest stiffness values are found in shrunken bone samples (immersed in acetone and ethanol). The mineral phase in bone thus resists tissue shrinkage that would otherwise occur in the pure soft tissue phase.
INTRODUCTION Recently, many attempts have been made to mimic the structure, and in turn, the unique set of mechanical properties, characteristic of mineralized tissues such as bone. These efforts at biomimesis have been hampered by a lack of fundamental understanding of the nanometer-scale structural organization and molecular interactions between tissue components. Although bone has been modeled as a two-phase composite material, there are three primary components to the structure: an inorganic mineral phase, an organic collagen phase, and water. The collagen phase in particular can be manipulated by soaking in polar solvents to alter hydrogen bonding in the higher-order protein structure. These alterations to hydrogen bonding in the protein have the potential to lead to changes in the tissue mechanical behavior [1-3]. Biological tissues have mechanical responses that are inherently time-dependent by virtue of the intrinsic hydration associated with physiological conditions. While the time-dependent response is dominant in soft tissues, it is also present in mineralized tissues such as bone. In mineralized tissues, the time dependence is often attributed to the hydrated collagen phase that comprises approximately half the tissue by volume [4]. Recent techniques have been developed for direct analysis of material time-dependence under indentation conditions [5] based on earlier analysis of elastic-viscoelastic correspondence for the contact mechanics problem as applied to polymeric materials [6,7]. Recent works have used
viscoelastic analyses for spherical indentation st
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