Evidence of entropic elasticity of human bone trabeculae at low strains

We performed 60 microtensile tests on 6 single trabeculae excised from a human femur head at various maximum tensile loads. The obtained results show a clear dependence of the calculated stress-strain behaviour from the applied load and thus from the mean stress over the cross section of the trabecula. The pooled data were found in good agreement with a combination of both the model of the nonlinear stress-strain behaviour of collagen fibrils and that for the modulus of elasticity of staggered mineralized collagen. This circumstance could also suggest a realistic explanation of the extreme variability found in literature for the elastic modulus of the trabecular material. In particular, when the trabeculae are solicited with relatively low stresses, their mechanical properties are mainly affected by the entropic elasticity of collagen molecules. This work offers both experimental data and a reasonable interpretation of the behaviour of fully mineralized tissue at low strains, that is up to about 0.1%.