WEB Studying structure-property relationships of bone on the nano- and microscale
Bone is a hierarchically architectured biological material that combines properties like stiffness, toughness and strength with a low specific weight. To better understand the mechanisms leading to this advantageous combination of attributes, its mechanical properties have to be investigated at all length scales.
Here, bone's anisotropic elastic and failure behavior was analyzed on the length scale of a single lamella (3-7μm). This was done based on microscopic mechanical experiments in both tension and compression of specimens produced by focused ion beam (FIB). A quantitative non-invasive method for the local estimation of collagen fibril orientation and degree of mineralization using Polarized Raman Spectroscopy (PRS) was developed and combined with site-matched micromechanical experiments in hydrated conditions to establish microscale structure-property relationships. Micropillar compression was furthermore performed in a range of strain rates representative of physiological loading up to impact or fracture events (0.0001-800/s).
A distinct tension-compression asymmetry in bone's strength and postyield behavior was observed with a reduced strength and ductility in tension. Strength anisotropy was clearly increased in tension compared to compression. Elastic modulus and strength were found to depend strongly on local collagen fibril orientation and could be well described by established composite models. A significant strain rate sensitivity was found when compressing micropillars oriented parallel to the local fibril direction, while the yield stress of transverse micropillars remained almost constant. These mechanical experiments were combined with post-test high resolution scanning electron microscopy (HRSEM) of fracture surfaces as well as scanning transmission electron microscopy (STEM) of tested specimens showing a strong influence of fibril orientation distribution, pores, and internal interfaces on the local failure morphology.
The information gained from these studies may be used to improve the fracture risk prediction of patients in a clinical setting through the development of multiscale models of bone strength. On the other hand, it offers fundamental insights into how nature designs hierarchical structures made of organic-ceramic nanocomposites to withstand continued mechanical loading that may be used in the development of architectured materials in the future.
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|Extended Abstract||This is an image showing the hierarchical structure of bone and some of the experimental results reported in the abstract.||2 MB||Download|