Solid-state NMR studies on the organic matrix of bone

Bone is a hierarchical architecture that consists of both inorganic and organic components. The organic components, including collagen and numerous non-collagenous biomolecules, are crucial for maintaining the mechanical strength and physiological functions of bone. The native structures of organic components and especially the mutual interactions between different components are important questions to be addressed. Among different analytical techniques, solid-state nuclear magnetic resonance (SSNMR) spectroscopy is a powerful tool to reveal the chemical and interactional information at an atomic level. Recent advancements of SSNMR technology and experimental protocols have brought great advances in understanding the molecular details in native bones. In this review, we summarize the progresses on the SSNMR studies of various organic components in the bone matrix. In the first part, we review the studies on collagen from four different aspects: (1) water-associated molecular dynamics; (2) the intrahelical/interhelical interactions in collagen residues; (3) the interactions between collagen and citrate; and (4) the cross-linking between collagen and inorganic surface. In the second part, we review the studies on the non-protein biomolecules including sugar species, citrate, lipids, and nucleic acids. In the end, we propose an outlook of future directions for SSNMR investigations on bones.