Chemical Microstructure of Cortical Bone Probed by Raman Transects

Abstract

Raman transects, microspectra taken at equal intervals along a line, are used to explore the microstructure of human cortical bone. Transects of 50 spectra taken at 2.5 μm intervals across an osteon show spatial differences in local mineral and protein composition as different physiological structures are traversed. Differences in mineral composition are seen near the rim of an osteon and further out in the lamellae. The blood vessel wall, primarily composed of collagen and elastin, is detected inside the Haversian canal. Factor analysis is used to explore the data set and reveals differences in mineral composition. Factor analysis also yields one bone matrix component, an osteoidal tissue component, and one blood vessel protein component. The 4 cm⁻¹ spectral resolution and 2.5 μm spatial sampling facilitate the development of univariate metrics for bone development and health. Band integration is performed for important marker bands including phosphate v₁ at 960 cm⁻¹, monohydrogen phosphate v₁ at 1003 cm⁻¹, B-type carbonate v₁ at ∼ 1070 cm⁻¹, collagen CH₂ wag at ∼ 1450 cm⁻¹, and collagen amide I at ∼ 1650 cm⁻¹. Mineral-to-matrix ratio, phosphate-to-monohydrogen phosphate ratio, and carbonate-to-phosphate ratio are calculated from these measured areas.