Hydration Effects on the Viscoelastic Properties of Collagen
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0898-L05-02.1
Hydration Effects on the Viscoelastic Properties of Collagen M.M.Ntim1, A.K.Bembey1, V.L.Ferguson1,2 and A.J.Bushby1 1 Department of Materials, Queen Mary, University of London, London, E1 4NS, UK 2 Department of Mechanical Engineering, University of Colorado, Boulder CO, USA
ABSTRACT The manner in which liquid interacts with collagen is unclear, with changes in hydration presenting ambiguity. At present, elastic modulus values for collagen quoted range from MPa to GPa. Dynamic mechanical analysis (DMA) of collagen in isolation provides an insight into the mechanical changes due to altered hydration states. Changes in the viscoelastic properties of collagen were examined as the material was systematically dehydrated in a series of water:solvent mixes to examine effects of dehydration. The effect of solvents with varying polarity was also examined. Tails from 11-week old wild type mice were used. Mouse tail is a tissue with a well-defined, hierarchical organization of type I collagen. The viscoelastic response of collagen was measured using dynamic mechanical analysis (DMA) in fiber extension mode over the frequency range of 1Hz to 10Hz. Samples were sequentially dehydrated in a series of solvent concentrations: 70% ethanol to 100% ethanol to 100% acetone and 70% ethanol to 70% methanol to 100% methanol for at least 1h. Selectively removing and then replacing water from collagen samples provides insight into the role of water in the ultrastructure of the tissue from the corresponding changes in the experimentally determined elastic modulus and viscous energy.
Key words: collagen, viscoelasticity, hydration, DMA
INTRODUCTION The mechanical response of bone exhibits time-dependent behavior, which is directly attributable to the organic hydrated collagen phase that comprises approximately half the tissue by volume. The viscous nature of a material is based on the relative molecular movement within the material. The relative molecular movement of collagen molecules and fibrils is likely restricted when bone dries and shrinks, decreasing the viscous energy. The influence of water on the mechanical properties of bone has been previously demonstrated with a factor of two change in the elastic modulus from wet to dehydrated state [1]. NMR studies have also shown that water can act as a plasticizer in collagen fibrils [2]. Both intra- and interchain hydrogen bonding within the triple helices of collagen has been thought to play an important role in forming the structure of collagen molecules, along with a highly ordered inner hydration layer of water molecules that form hydrogen bonds along peptide chains [3]. Water has been shown to form hydrogen-bonded bridges, which further contribute to the structure of collagen by forming intra- and interchain links within molecules, along with intermolecular bridges between neighboring triple helices that may contribute to the structure and properties of the collagen fibrils.
0898-L05-02.2
Due to its long chain structure, collagen exerts a strong influence on the vi
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