Bio & Nano Materials Research Lab

A multi-scale experimental work was carried out to characterize cortical bone as a heterogeneous material with hierarchical structure. We analyzed bone at several different length scales: nanoscale (1 nm -100 nm, apatite crystal and collagen fibril level), sub-microscale (1-10μm, single lamella level), microscale (10 -500μm, single osteon level), and mesoscale (1–10 cm, involving a random arrangement of osteons, lamellar bone and/or woven bone, representing cortical bone). Macroscale level represents a whole bone level which includes both cortical and trabecular bones. Samples prepared from swine femoral cortical bones from three age groups (6-month, 12-month and 42-month) were used to study the age-related changes. The mechanical properties of cortical bone at meso-scale were measured by tensile and compression testing and the modulus and hardness were measured at the single lamella level using nanoindentation. Scanning electron microscopy (SEM) and micro-computed tomography (micro-CT) were used to analyze the structural variations in bones from different age groups from sub-micro to meso-scale levels. The bone’s chemical composition and its spatial distribution were characterized by combining the ash content method, Duel Energy X-ray Absortionmetry (DEXA) and Fourier transform infrared microspectroscopy (FTIRM). These experimental results indicated significant age-related changes in both structure and chemical composition of cortical bone.  Woven bone was dominant in 6-month samples, lamellar bone was a prevalent structure in 12-month old samples, while osteons were features in the 42-month old samples. The mineral: organic ratio increased as bone matured. The superior bone structure and high mineralization level led to the increase in the elastic modulus.