Unraveling Water-Mediated ³¹P Relaxation in Bone Mineral

Abstract

Bone is a dynamic tissue composed of organic proteins (mainly type I collagen), inorganic components (hydroxyapatite), lipids, and water that undergoes a continuous rebuilding process over the lifespan of human beings. Bone mineral is mainly composed of a crystalline apatitic core surrounded by an amorphous surface layer. The supramolecular arrangement of different constituents gives rise to its unique mechanical properties, which become altered in various bone-related disease conditions. Many of the interactions among the different components are poorly understood. Recently, solid-state nuclear magnetic resonance (ssNMR) has become a popular spectroscopic tool for studying bone. In this article, we present a study probing the interaction of water molecules with amorphous and crystalline parts of the bone mineral through 31 P ssNMR relaxation parameters ( T 1 and T 2 ) and dynamics (correlation time). The method was developed to selectively measure the 31 P NMR relaxation parameters and dynamics of the crystalline apatitic core and the amorphous surface layer of the bone mineral. The measured 31 P correlation times (in the range of 10 –6 –10 –7 s) indicated the different dynamic behaviors of both the mineral components. Additionally, we observed that dehydration affected the apatitic core region more significantly, while H–D exchange showed changes in the amorphous surface layer to a greater extent. Overall, the present work provides a significant understanding of the relaxation and dynamics of bone mineral components inside the bone matrix.

1H‐13C cross‐polarization kinetics to probe hydration‐dependent organic components of bone extracellular matrix

“…The effect of dehydration and the H/D exchange process on the fresh native bone was described in the literature. [31,34,45,46] Our experimental results are also in accordance with the previous studies.…”

“…These flakes had the same morphology similar to the intact bone. [32][33][34] Three types of bone samples were included in the current study: Fresh hydrated native bone, dehydrated bone, and H/D exchanged bone. Fresh hydrated native bone was not treated in any way and was tested within 1 h of being extracted from the animal.…”

“…To obtain the H/D exchange bone sample, the fresh bone sample was incubated in D 2 O solution (Sigma Aldrich, USA) for 72 h at 200 rpm using an incubator shaker (Scigenics Biotech, India) that promotes the greatest amount of water-D 2 O exchange. [34] For additional ssNMR investigations, all the samples were placed into a 3.2-mm zirconium rotor.…”