Age-dependent mechanical heterogeneity in immature murine bone: A nanoindentation mapping study

While bone mechanical properties during adulthood are well-documented, the mechanical properties of immature bone during infancy and adolescence remain poorly characterized. In this study, nanoindentation mapping was performed to measure the indentation modulus (E) and hardness (H) across four anatomical quadrants (anterior, posterior, medial, and lateral) in the tibial cortical bone of female C57BL/6J mice at postnatal ages of 3, 7, 14, 21, and 56 days (6 mice per age group). Two-way ANOVA revealed no significant interaction between age and anatomical location for E (p = 0.946) or H (p = 0.769), whereas age demonstrated a significant main effect on both E (p < 0.001, η² = 0.528) and H (p < 0.001, η² = 0.111). Results demonstrated a significant age-dependent increase in E across all anatomical quadrants (p < 0.001), while H showed no consistent developmental trend. Linear regression models revealed differential growth trajectories in E among quadrants, with medial and lateral quadrants exhibiting slightly faster increases. These findings may provide some insights into the developmental biomechanics of immature bone and establish a foundation for multiscale modeling of skeletal growth.