Kyle Strodtbeck with David Farrell

Measuring the Density of Bone

Density is a fundamental property of condensed matter and some recent work suggests that there may be a direct relationship between it and magnetic susceptibility for biological materials. Magnetic susceptibility may therefore provide a method to image the density of the human body, which would be of considerable value in medical diagnostics. However, checking this relationship requires measuring the in-vitro density of biological samples. Because of their porous structure, inhomogeneity, and restricted lifetime, this is a challenging task. The present investigation is focused on bone, which offers the most stable biological material for physical measurements. In preliminary studies, using the standard water immersion method, it has been found that changes in density of several percent can occur on immersing bone samples in water. Furthermore, these changes are not a monotonic function of immersion time, presumably reflecting a complex interplay between the diffusion of water into the sample, which tends to increase the density, and sample expansion, which has the opposite effect. Bone samples will be collected, for a variety of different species, and a specially designed container will be utilized to accurately determine their density at room temperature. Careful attention will be paid to reproducibility and experimental uncertainties. The non-monotonic behavior mentioned will be studied and compared between species to see if understandable patterns emerge. Depending on the progress made with these bone studies, the experiment may be extended to the more difficult case of (soft) biological material.