Mechanistic insights into the synergistic Determinants of bone Biomechanics: Multi-level characterization and multi-parameter composite factor model in immature murine tibiae.

The chemical composition, structure, and mechanical properties of mature bone are well established. However, predictive models for the mechanical properties of developing bone-characterized by active mineralization and structural remodeling-remain incomplete. This study integrated high-resolution Micro-CT, high-throughput nanoindentation, and confocal Raman spectroscopy to systematically map the spatial heterogeneity of structure, chemical composition, and mechanical properties in tibiae from 6-week-old female C57BL/6J mice. Multi-parameter composite factor models were proposed to predict the elastic modulus and hardness. The results indicated that single structural or chemical composition parameters exhibited limited explanatory power for elastic modulus (R2 ≤ 0.346) and hardness (R2 ≤ 0.37). In contrast, integrating structural and chemical descriptors significantly improved model performance, achieving R2 values of 0.746 for elastic modulus and 0.814 for hardness, underscoring a coordinated structure-chemistry interplay during bone development. Notably, significant gradients in the circumferential direction of mineralized matrix ratio and carbonate substitution degree (p < 0.01) did not result in heterogeneous mechanical properties, reflecting a dynamic balance mechanism that supports structural growth while maintaining mechanical integrity. This work provides mechanistic insight into the developmental adaptation of immature bone and establishes a theoretical foundation for advanced fracture treatment strategies and biomimetic bone repair materials.