Dehydration-Induced Structural Changes in the Collagen-Hydroxyapatite Interface in Bone by High-Resolution Solid-State NMR Spectroscopy

Study of interactions among different components of amorphous biomaterial such as bone is important to understand the mechanism of its formation and biomineralization process and for its unique mechanical properties. In this article, we present dehydration-induced structural changes at the interface of the collagen protein and hydroxyapatite interface in intact mammalian bones by high-resolution solid-state NMR (SSNMR) spectroscopy. With recent advances in SSNMR methodologies, this is the only spectroscopic technique which can provide atomic piercing structural details on amorphous systems such as bone. We performed three SSNMR experiments on bone samples with different degrees of hydration level to probe comparative structural changes. One of the SSNMR experiments is a (13)C{(31)P} Rotational Echo Double Resonance (RED OR) SSNMR experiment which gives an estimate of distances between collagen protein side chain residues and the hydroxyapatite surface in bone. Other SSNMR experiments such as relaxation measurement (T(2) measurement) of (13)C resonances of collagen protein along with (1)H chemical shift measurement give structural changes in the bone matrix due to dehydration. These experiments were performed on bone samples with different degree of water content and also on bone samples in which water was exchanged with D(2)O, thereby reducing the strength of the hydrogen bonding network: We find that when water molecules from the bone matrix are removed the distance of collagen with the hydroxyapatite surface decreases significantly. The present study explains the role of water in stabilizing the structural properties of amorphous biomaterial like bone and will help in synthesizing bone implant materials with desired properties.