Time-Resolved Dehydration-Induced Structural Changes in an Intact Bovine Cortical Bone Revealed by Solid-State NMR Spectroscopy
Peizhi Zhu†, Jiadi Xu†‡, Nadder Sahar§, Michael D. Morris*†§, David H. Kohn§ and Ayyalusamy Ramamoorthy*†‡
Understanding the structure and structural changes of bone, a highly heterogeneous material with a complex hierarchical architecture, continues to be a significant challenge even for high-resolution solid-state NMR spectroscopy. While it is known that dehydration affects mechanical properties of bone by decreasing its strength and toughness, the underlying structural mechanism at the atomic level is unknown. Solid-state NMR spectroscopy, controlled dehydration, and H/D exchange were used for the first time to reveal the structural changes of an intact piece of bovine cortical bone. 1H spectra were used to monitor the dehydration of the bone inside the rotor, and high-resolution 13C chemical shift spectra obtained under magic-angle spinning were used evaluate the dehydration-induced conformational changes in the bone. The experiments revealed the slow denaturation of collagen due to dehydration while the trans-Xaa-Pro conformation in collagen remained unchanged. Our results suggest that glycosaminoglycans in the collagen fiber and mineral interface may chelate with a Ca2+ ion present on the surface of the mineral through sulfate or carboxylate groups. These results provide insights into the role of water molecules in the bone structure and shed light on the relationship between the structure and mechanics of bone.