Investigation into compositional and mechanical property differences of the microstructure in two strains of mouse femoral bone

Melanie A. Patel

doi:10.17918/etd-4123

Hierarchical linkages of bone structure and mechanical properties at lower length scales to macroscopic properties remain poorly understood [1, 2]. Critically assessing the bone architecture at different length scales using a combination of advanced materials characterization techniques is necessary to study connections between bone structure and properties. The gap in understanding these linkages from higher length scales to microscopic features is clearly needed for assessing bone health. Oftentimes fracture risk is assessed using Dual-Energy X-ray Absorptiometry (DXA) to measure bone mineral density (BMD) [3]. Bone strength is not accurately described solely by BMD as evidenced by the fact that BMD only accounts for 60-70% of variation in bone strength [3]. More attention must be paid to understanding bone quality, looking at tissue and matrix level composition as well as geometry, assessing tissue quantity and distribution [4]. This research is preliminary work aimed at establishing methodologies for reliably assessing bone composition and mechanical structure at the microscale. Two strains of inbred mice were chosen as the bone model because they offer an identical genome within a strain and are well-established in bone disease research [5]. The bulk of this research focuses on using Raman spectroscopy to assess compositional differences between two strains of inbred mouse femoral bone. These strains were selected because of their known macroscopic property differences. Looking at the postero-lateral cortex, areas of newly formed bone and matured bone are sampled using line maps. This captures the entire formation process of bone from deposition to resorption. Particular attention was paid to impurities of the crystal lattice, carbonate and monohydrogen phosphate. Typically, B-type carbonate substitution is studied since it makes up the bulk of impurities in the phosphate lattice [2]. This research investigated monohydrogen phosphate impurities as well, looking at the maturation process of the mineral across the bone cortex. Mineral to matrix ratios were also assessed to determine peak level of mineralization in each strains. 2-D maps of mineral to matrix composition gave more insight into the bone formation process between strains. Lastly, nanoindentation tests were performed to elucidate the modulus of the material from the postero-lateral cortex, again sampling bone from the depositional edge to the resorption edge. This gives a good picture of the difference in modulus between newly laid down bone versus fully mineralized bone. The AJ strain should show an increased mineral to matrix ratio and modulus since it has a higher ash content versus the B6 strain. The mineral maturation process in both strains is not well known so it will be interesting to see which strain has higher level of impurities in the crystal lattice.

Investigation into compositional and mechanical property differences of the microstructure in two strains of mouse femoral bone

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Investigation into compositional and mechanical property differences of the microstructure in two strains of mouse femoral bone

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