Laboratory for the Study of Skeletal Disorders and Rehabilitation, Summary of Current Research

Our group has devoted to the application of Nuclear Magnetic Resonance (NMR) spectroscopy and Nuclear Magnetic Resonance Imaging (MRI) to basic science and clinical problems of bone mineral and matrix, and to the diseases associated with bone. NMR spectroscopy provides an analysis of the ionic composition and structure of the mineral crystals and matrix, i.e., the properties of bone as a material or substance, while MRI yields the spatial properties of bone as a tissue based on the spatial variation of the NMR signals of bone. The chemistry of calcium phosphate salts, in particular the apatite minerals, is highly complex. Many of the biological and mechanical functions of bone mineral are controlled by the composition and crystal structure of the calcium phosphate bone mineral crystal. Issues relating to bone mineral chemistry and bone resorption carry important implications for public health. It has long been established that bone mineral crystals are compositionally and structurally similar to the synthetic mineral calcium hydroxyapatite, Ca 10 (OH) 2 (PO 4) 6. However, in contrast to typical synthetic hydroxyapatite, bone mineral is nanocrystlline, structurally disordered, and compositionally nonstoichiometric. It exhibits a high specific surface containing labile chemical groups, and a remarkable ability to support ionic vacancies and substitutions. A decades-old controversy concerning the relationship between bone mineral and hydroxyapatite is whether bone mineral crystals contain hydroxyl (OH-) ions. Although the OH-content of hydroxyapatite itself is readily measurable with wet chemical and instrumental techniques, such measurements on the biological apatite crystals of bone suffer interference from the organic matrix, which contains variable amounts of water and complex mixture of proteins (primarily collagen I) and other biopolymers as well as small molecules. Both the matrix and the water interfere with wet chemical and infrared analysis for OH-in the crystalline phase. Hence, most studies of the OH-content of bone mineral require removal of the water by drying and removal of the organic matrix (" deproteinization ") by chemical pretreatment to yield " anorganic " bone. Such chemical treatment always raises the question of whether the mineral has been chemically altered. We have demonstrated that a two dimensional solid state