Thermal perturbations to bone mineral crystal structure studied by Raman and NMR spectroscopies

As part of an ongoing larger study of the molecular and supramolecular foundations of bone tissue biomechanics, we report thermal perturbations to bone mineral and related model compounds. The response of bone tissue to external mechanical and thermal loading under a variety of conditions is used to elucidate the response to physiologically relevant loads. Here NMR spectroscopy is used in conjunction with Raman spectroscopy to elucidate the mineral structure of the bone and track changes in the lattice due to temperature variation. Changes in the bone lattice are studied by examining the Raman spectral band widths and positions of the phosphate and carbonate bands. Expansion of the lattice leads to increased band widths as local ion motion is facilitated. Larger effects are found in undeproteinated bone powder than in deproteinated bone mineral powder. 1H MAS NMR is used to track the water content of deproteinated bone as a function of temperature. The differing effects observed in undeproteinated bone powder and deproteinated bone mineral powder suggest that mineral crystallite expansion may involve mechanical constraint by the bone matrix. 13C MAS NMR spectroscopy revealed a loss of carbonate in deproteinated bone mineral when heated to 225 C. This is a significantly lower temperature than previously reported for removal of carbonate from synthetic apatite material. The properties of bone mineral influenced by even small perturbations such as temperature elevation or reduction depend on the presence of matrix. It is reasonable to assume that bone tissue response to other external loads, including compression or bending under normal physiological conditions also depend on the interaction of mineral and matrix.