Time-dependent mechanical properties of rat femoral cortical bone by nanoindentation: An age-related study

The aim of this study is to assess the time-dependent mechanical properties of rat femoral cortical bone in a lifespan model from growth to senescence. New nanoindentation protocol was performed to assess the time-dependent mechanical behavior. The experimental data were fitted with an elastic-viscoelastic- plastic-viscoplastic mechanical model allowing the calculus of the mechanical properties. Variation of mechanical response of bone as a function of the strain rate and age were highlighted. The most representative variations of the mechanical properties with age were found to be statistically significant (P < 0.001) from 1 to 4 months for elastic properties, from 1 to 9 months for viscoelastic properties and during all lifespan for plastic and viscoplastic properties, highlighting different maturation ages for elastic, viscoelastic, plastic and viscoplastic behaviors. These results suggest that different physical-chemical and structural processes occur at different ages reflecting bone modeling and remodeling activities in the rat's whole lifespan.