Role of Collagen In Hierarchical Structure, Composition, And Biomechanics Of Bone

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Bone is a complex tissue composed of mineral and collagen. Bone fragility represents a significant societal burden, and is commonly, but incompletely diagnosed through changes in bone mass and structure. Understanding the contributions and interactions of collagen and mineral at the nanostructural level is critical for understanding how factors beyond bone mass govern bone fragility. Collagen formation and incorporation into bone is highly regulated, and changes in collagen or collagen-related proteins leads to the bone disease osteogenesis imperfecta (OI), exemplified by extremely high bone brittleness and fragility. Understanding how changes in collagen and mineral interactions lead to bone brittleness will provide a greater understanding of how bone content, structure, and mechanical properties interact at multiple length scales. This project introduces a novel use of atomic force microscopy-based infrared spectroscopy (AFMIR) and positron annihilation lifetime spectroscopy (PALS) to detect changes in collagen-mineral interactions in bone. By understanding how these processes break down in models of OI, this research will have a broader impact by identifying key factors that are most closely correlated with bone brittleness and fragility in more common diseases such as osteoporosis.This research will determine how collagen governs bone material properties across multiple size scales. We hypothesize that bone brittleness is regulated through changes across the hierarchical organization of bone originating at the level of the collagen-mineral interaction. To test the hypothesis, mice with defects in collagen helical structure, pro-collagen processing, or post-translational hydroxylation will be studied by AFM-IR and PALS imaging. Hierarchical phenotype analysis will be performed across multiple length scales and will identity factors most closely correlated with the mild, moderate, and severe bone brittleness found in these mice. Collagen fibril structure will be directly visualized in the context of its surrounding matrix chemistry, tissue stiffness, and local fibril organization by AFM-IR. PALS will describe void size and distribution at this same size scale. Together, these techniques will be integrated with higher order contextual information including tissue organization (woven-lamellar patterns), porosity (of vascular and cellular origin), tissue mineral, and stiffness through histologic, nanoCT, and nanoindentation techniques. The intellectual significance of this project arises from understanding how collagen governs bone material properties across multiple size scales and will provide foundational understanding regarding the basic biological principles behind bone formation, growth, and maturation.