Poroelastic Indentation Analysis for Hydrated Biological Tissues
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0975-DD07-05
Poroelastic Indentation Analysis for Hydrated Biological Tissues Michelle L. Oyen1, Amanpreet K. Bembey2, and Andrew J. Bushby2 1 Engineering Dept., University of Cambridge, Trumpington Street, Cambridge, CB2 1PZ, United Kingdom 2 Queen Mary, University of London, London, E1 4NS, United Kingdom
ABSTRACT Indentation techniques are employed for the measurement of mechanical properties of a wide range of materials. In particular, techniques focused at small length-scales, such as nanoindentation and AFM indentation, allow for local characterization of material properties in heterogeneous materials including natural tissues and biomimetic materials. Typical elastic analysis for spherical indentation is applicable in the absence of time-dependent deformation, but is inappropriate for materials with time-dependent responses. Recent analyses for the viscoelastic indentation problem, based on elastic-viscoelastic correspondence, have begun to address the issue of time-dependent deformation during an indentation test. The viscoelastic analysis has been shown to fit experimental indentation data well, and has been demonstrated as useful for characterization of viscoelasticity in polymeric materials and in hydrated mineralized tissues. However, a viscoelastic analysis is not necessarily sufficient for multi-phase materials with fluid flow. In the current work, a poroelastic analysisóbased on fluid motion through a porous elastic networkóis used to examine spherical indentation creep responses of hydrated biological materials. Both analytical and finite element approaches are considered for the poroelastic Hertzian indentation problem. Modeling results are compared with experimental data from nanoindentation of hydrated bone immersed in water and polar solvents (ethanol, methanol, acetone). Baseline (water-immersed) bone responses are characterized using the poroelastic model and numerical results are compared with altered hydration states due to polar solvents.
INTRODUCTION Instrumented indentation (ënanoindentationí) testing, in which load and displacement are monitored during contact of a probe with a material surface, is a popular technique for measurement of local mechanical properties of a wide variety of materials. This has been due in part to the wide-spread availability of commercial instruments for small-scale contact testing, and the development of routine analytic techniques for elastic-plastic [1,2] and viscoelastic [3-6] mechanical property deconvolution.
Due to the possibility of localized testing and property mapping, nanoindentation testing is particularly well-suited for characterizing the local mechanical properties of biological materials, which can vary at nm- to µm length-scales [7,8]. However, as the mechanical response of biological materials is dominated by time-dependent mechanical deformation during reasonable experimental time-frames, this time-dependence must be considered explicitly in the indentation analysis. Recent works have used viscoelastic analyses [3-6] for spherical inden
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