In-Situ Anaerobic Heating of Human Bones Probed by Neutron Diffraction

Abstract

The first neutron diffraction study of in-situ anaerobic burning of human bones is reported, aiming at an interpretation of heat-induced changes in bone, which were previously detected by vibrational spectroscopy, including inelastic neutron scattering techniques. Structural and crystallinity variations were monitored in samples of the human femur and tibia, as well as a reference hydroxyapatite, upon heating under anaerobic conditions. Information on the structural reorganization of the bone matrix as a function of temperature, from room temperature to 1000 °C, was achieved. Noticeable crystallographic and domain size variations, together with O-H bond lengths and background variations, were detected. Above 700 °C, the inorganic bone matrix became highly symmetric, devoid of carbonates and organic constituents, while for the lower temperature range (<700 °C), a considerably lower crystallinity was observed. The present pilot study is expected to contribute to a better understanding of the heat-prompted changes in bone, which can be taken as biomarkers of the burning temperature. This information is paramount for bone analysis in forensic science as well as in archeology and may also have useful applications in other biomaterial studies.

Figure 1

Experimental setup for the in-situ heating process of human bone samples, under controlled anaerobic conditions (vacuum), while measuring the corresponding neutron diffraction data at defined temperature points on the GEM neutron diffractometer; (a) layout of six ZnS/⁶Li scintillator detector arrays; (b) loading of the samples on GEM.

Figure 2

(a) Hydroxyapatite structure with Ca atoms displayed as gray spheres, hydrogen atoms in white, and P atoms inside oxygen (red spheres) tetrahedra. O4 and H4 atom positions at specific sites of the crystal structure are highlighted. (b) Section of human tibia burned at 1000 °C under anaerobic conditions. Neutron diffraction patterns at room temperature (RT) and after in-situ anaerobic burning at temperature points 400, 700, and 1000 °C, for (c) reference hydroxyapatite (HAp, SRM 2910b) data offset in y for clarity, (d) human femur (F42) data offset in y for clarity, (e) human tibia (T42) data offset for clarity. Bottom row: Rietveld refinement profiles of GEM histogram 4 at 1000 °C for: (f) HAp, (g) F42 and (h) T42.

Figure 3

Plots of structure parameters during in-situ burning as a function of temperature, of hydroxyapatite, human femur, and human tibia: (a) hydroxyapatite structure; (b) a = b cell parameter; (c) c cell parameter; (d) unit cell volume; (e) γ₂ value for histogram 5; (f) γ₂ value for histogram 6; (g) OH bond length; (h) H4 fraction; and (i) O4 fraction. The lines through the data points are a guide to the eye.

Figure 4

Crystallographic domain dimensions and background variations during in-situ burning as a function of temperature for hydroxyapatite, human femur, and human tibia: (a) schematic representation of the domains; (b) domain size - hist#5; (c) domain size - hist#6; (d) background percentage changes. The lines through the data points are a guide to the eye.