Probing the Role of Bone Lamellar Patterns through Collagen Microarchitecture Mapping, Numerical Modeling, and 3D‐Printing

The fibrillar organization is crucial for the mechanics of osteonal bone and for its anisotropy. Different collagen fiber orientation (CFO) patterns are observed in bone and correlated to the main local loading, leading to the hypothesis that the fibers are preferentially aligned to bear specific loading types. A heterogeneous distribution of osteon morphotypes (OMs) is noticed in long bones, although the relationship between the OM spatial distribution and the local predominant loading is still unclear. This study aims to shed light on the reasons why Nature uses specific OMs in diverse stress-dominated regions. A multimodal approach is adopted, including collagen fiber orientation mapping, numerical modeling of different OMs under tensile and compressive loading, and 3D-printing of OM-inspired samples, to unravel the relationship between different OMs and their mechanical behavior. Simulation results suggest a better performance of the vertical OM (VOM) under tensile loading and of the twisted OM (TOM) under compression, confirming earlier hypotheses. The outcomes of mechanical testing, conducted on 3D-printed samples, highlight a possible buckling-induced failure of fibers with preferential vertical orientation and provide evidence that OMs are stress-tailored, opening new venues for the design of stress-tuned bioinspired composites.