Mechanical Behavior of Osteoporotic Bone at Sub-Lamellar Length Scales

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 microscopy and mechanically tested in compression using an atomic force microscope while observing them using in situ electron microscopy. This experimental approach was shown to be effective for 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. Surprisingly, the increased strain to failure for osteoporotic bone material provided enhanced toughness relative to the control samples, suggesting that lowering of bone fragility due to osteoporosis is not defined by material performance. 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.

The Ultrastructure of Bone and Its Relevance to Mechanical Properties

“…Experimental validation of the mechanical properties of bone at the nanoscale is also very challenging. Relevant experimental studies include atomic force microscopy measurements combined with electron microscopy imaging (SEM and TEM) (e.g., [58][59][60]) and tests on micropillars of bone at a µm scale [61][62][63]. Theoretical models can give valuable insights on bone's response at the nanoscale and the structure-property relations of bone in general.…”

Molecular force transfer mechanisms in graphene oxide paper evaluated using atomic force microscopy and in situ synchrotron micro FT-IR spectroscopy

“…37 This setup essentially used an AFM orientated 90°along its horizontal axis and was situated under an in situ synchrotron micro FTIR (B22 beamline, Diamond Light Source, UK) that evaluated structural changes in the GO paper. Mechanical testing was performed as previously reported 21,23 by first placing an uncured droplet of epoxy glue (Poxipol, Arg.) approximately 1-2 mm in diameter at the edge of the AFM sample stage.…”

“…Recent progress in experimental mechanics has been used to deform discrete volumes of GO, isolated using focused ion beam (FIB) microscopy, to failure using atomic force microscopy (AFM) 21 . This work applied strategies previously developed for determining specific component mechanics in multi-phase systems, including individual nanofibers in bone 22 and simple composite volumes in mineralized tissues 23 , and is considered advantageous for understanding inherent GO paper behavior as relatively small samples prepared using FIB are devoid of large defects present when testing at the macroscale. However, AFM mechanical testing of GO paper at small length scales currently lacks the structural information previously examined in computer simulations despite having sufficient force resolution to determine molecular mechanisms.…”

Effects of thermomechanical history and environment on the fatigue behavior of (β)-Ti-Nb implant alloys

“…Major advantage of these properties is the minimization of "stress shielding effects", which can lead to bone atrophy, impaired healing and consequently premature failure or loosening of implants due to the high difference of Young's moduli compared to the cortical bone [1][2][5][6][7][8]. This is particularly important in case of implants for osteoporotic bones, which have a lower mass and density then the healthy bone and consequently an even more reduced stiffness corresponding to elastic modulus values <10 GPa [9].…”