Characterization and comparison of hyper-viscoelastic properties of normal and osteoporotic bone using stress-relaxation experiment.

Bone tissue behavior under various loads is nonlinear elastic due to irreversible energy absorption. Also, viscoelasticity is one of the most important properties of bone which is very important in dynamic analyses and helps a lot in making artificial bone. In this study, rat tibia bone specimens were subjected to compression stress-relaxation test for normal (n = 5) and osteoporotic (n = 5) groups in order to characterize their mechanical properties using finite element modeling coupled with an optimization algorithm. Using this method, the structural equation parameters for the Neo-Hookean model and the Prony series coefficients were used to describe the hyper-elastic and the viscoelastic behavior of specimens, respectively; moreover, the properties of materials including the bulk, shear and Young's moduli for both groups were obtained and compared. The shear modulus was also gained as a function of time. In addition, the percentage of stress reduction and its relation to the initial stress were investigated for specimens. Finally, the effect of changes in each of the parameters of the hyper-viscoelastic structural equation on the force response was determined. Results of this study can be used in predicting the transient response and dynamic analysis of the bone.

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