OBSERVATION OF MECHANICAL RESPONSES OF MINERAL AND COLLAGEN PHASES IN BONE TISSUE BY LASER RAMAN IMAGING
Masahiro Todoh, Shigeru Tadano
Hokkaido University, Japan
Bone is often regarded as a composite material consisting of mineral particles and organic matrix of mainly Type I collagen in microscopic scale. The mechanical properties of bone tissues in macroscopic scale depend on the structural organization and properties of constituents in the microscopic scale. Raman spectroscopy is known as useful tool for the analysis of material at ultra-structural level. The aim of this study are to observe the mechanical behaviors of mineral and collagen phases in bone tissues by using Raman imaging system and to investigate the effect of structural anisotropy of cortical bone on the mechanical responses. Cortical bone specimens of bovine femoral diaphyses (Age: 23 m.o.) were prepared with a size of 10.0(L) x1.0(W)x0.5(T) mm, where the longer edges of specimens were aligned to the parallel or perpendicular to the femoral axis. Raman microscope system was used for the analysis of mechanical response of bone tissue under tensile loading by the micro-tensile device. Imaging area was 60x60 μm and measurement points were 41x41 at 1.5 μm intervals. Raman shifts of specific seven Raman peaks were calculated from apatite crystal and collagen molecule in bone matrix. From all experiments, the Raman shifts of mineral and collagen phases to lower wave numbers were observed with increase of applied tensile stress. The changes in Raman shifts under femoral axial stress were relatively smaller than that under circumferential stress. Also, the changes in Raman shifts against applied tensile load was distributed as gaussian distribution in the measurement area. From these results, the Raman shifts distribution of mineral and collagen phases in bone tissues were well related to the applied tensile stress. In addition, those relationships were dependent to the structural anisotropy of cortical bone.