Bone: ultrastructure, chemistry and isotopes

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Bones are built of two components, a hard calcium phosphate mineral called hydroxyapatite (HA), and a weaker protein, collagen. Knowledge of how these components are woven together in animal and human bone is important in understanding the growth and development of bone and in diseases of bone. We have discovered that most of the HA in bone is in the form of long, thin plates which surrounds and reinforce columns (fibrils) of collagen. In our research we will focus on working out the details of this pattern as it varies with age and skeletal location, and between different species. We will also delve inside these HA-rich plates to learn how they are put together, as we have also shown that they are not single crystals but rather packages of many even smaller crystals. We will also study two other aspects of bone. We have shown that citric acid is an important constituent of bone making up as much as 2% of all bones. Its function is still unknown although it is probably required to maintain the qualities of bone crystals. We will try to find how it gets into bone, where it is located, and how it functions. Citrate gradually disappears after death and burial of the bone. We have shown that we can date forensic bone samples from their citrate concentration to tell the time since death. We will try to determine how the citrate is lost and how the rate of loss varies with the conditions of burial, to broaden the applicability of this method in solving crime. Also, we will study how the ratio stable isotopes of oxygen (18O/16O) varies in bones and teeth depending on where people were living, as a way to trace migration of people, and apply this to solve problems in archaeology and forensic science. This is a concerted, multifaceted program which applies novel methods from geochemistry, mineralogy and material science to bear on the study of bone.