Abstract
Osteoporosis is a disease known to promote bone fragility but the effect on the mechanical properties of bone material, which is independent of geometric effects, is particularly unclear. To address this problem, micro-beams of osteoporotic bone were prepared using focused ion beam (FIB) microscopy and mechanically tested in compression using an atomic force microscope (AFM) while observing using in situ electron microscopy. This experimental approach was shown to be effective at measuring the subtle changes in the mechanical properties of bone material required to evaluate the effects of osteoporosis. Osteoporotic bone material was found to have lower elastic modulus and increased strain to failure when compared to healthy bone material, while the strength of osteoporotic and healthy bone was similar. A mechanism is suggested based on these results and previous literature that indicates degradation of the organic material in osteoporosis bone is responsible for resultant mechanical properties.
Highlights
Osteoporosis is one of the most significant types of bone disease that causes degradation of bone’s mechanical function
Stress is calculated by dividing the force applied to the sample from the atomic force microscope (AFM) tip by the cross-sectional area of the micro-beam sample, measured from scanning electron microscopy (SEM), whereas strain is calculated by dividing the change in length by the total micro-beam sample length, as shown in Eqs 1 and 2 below
Where σ is the stress in the compressed micro-beam sample, f is the force applied by the AFM, A is the micro-beam cross-sectional area, ε is the strain in the bone micro-beam, ∆L is change in length of the beam, and L0 is the original length of the bone microbeam prior to mechanical deformation
Summary
Osteoporosis is one of the most significant types of bone disease that causes degradation of bone’s mechanical function. The disturbances in osteoporotic bone structure are known to be due to changes in metabolic conditions such as hormonal changes (decrease in estrogen levels, growth hormone deficiency, increase in parathyroid hormone), steroids (glucocorticoid deficiency), diet, and lifestyle (reduction in calcium intake, lack of vitamin D, sedentary lifestyles) (Hauge et al, 2003; Iacono, 2007). Both Type I and Type II osteoporosis share the common effect of increased susceptibility to catastrophic fracture in bone
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