Material anisotropy and elasticity of cortical and trabecular bone in the adult mouse femur via AFM indentation

This paper investigates the elastic properties of bone tissue in the adult mouse femur through Atomic Force Microscopy (AFM) indentation with the goal of understanding its microstructure and underlying mechanics at the nano length scale. Both trabecular and cortical bone types are studied. In particular, we examined the elasticity of cortical bone and individual trabeculae in the longitudinal and transverse directions of the samples. For cortical bone, the elastic modulus in the longitudinal direction was found to be 10-15% higher than that in the transverse direction; for trabecular bone, this difference was 42%. For the trabeculae, this value was found to be in a lower range (0.92 +/- 0.22 GPa). As per the transverse elastic modulus, an average of 1.58 +/- 0.36 GPa was measured for cortical bone, and 0.55 +/- 0.21 GPa for trabecular bone. The anisotropy ratio was within the range of 1.2-1.5 for cortical bone and 1.7-2 for trabecular bone. While the elastic modulus of cortical bone varied along the length of the femur with up to 30% variation, no significant differences were observed within each transverse section. The effect of indentation frequency (1-500 Hz) on the longitudinal elastic moduli was also investigated for cortical and trabecular bone, with results showing a correlation between indentation frequency and elastic modulus. Statement of significance: This study examines the adult mouse femur with a twofold aim: to investigate the anisotropy and inhomogeneity of cortical and trabecular bone tissues and to elucidate their elastic behavior at the nanometer length scale. The elastic moduli of cortical bone and individual trabecula are measured in the longitudinal and transverse cross-sections via AFM indentation at selected locations and in specific directions of the adult mouse femur. The results provide insights into the relationship between mechanical properties and structural morphology of cortical and trabecular bone tissue.