RESEARCH

Our research is bridging the gap between fracture mechanics, material characterization and biology. We aim at investigating the structure, function mechanisms and dynamics of skeletal tissues using an experimental multi-scale approach.

Since skeletal tissues and biological materials derive their structural integrity from the molecular to millimetre length-scales, we investigate their hierarchical structure, deformation/fracture mechanisms, and biological activities using advanced x-ray synchrotron instrumentations designed to capture behavior at these multiple dimensions as well as macroscale mechanical testing (strength, toughness and fatigue tests).

Using this multi-scale experimental approach, we have successfully explored highly diverse biosamples (bones from human and animal models, intervertebral discs, fish scale, skin, mantis shrimp telson, etc.) and bone fragility associated with diseases (osteonecrosis, diabetes, osteoporosis, osteogenesis imperfecta), treatments (bisphosphonate and corticosteroid) or Fatigue loading. This work provided a foundation for understanding mechanisms by which the bone’s resistance to fracture can be impaired by disease or treatment.

Synchrotron-based engineering science is pushing the limits of knowledge in biological sciences and others new possibilities for scientifc discovery.

Keywords: Stress and fatigue fracture mechanics, Skeletal biomechanics, Bone quality and bone fragility, Synchrotron radiation micro-tomography, Synchrotron radiation x-ray scattering, From cellular to macroscopic scales


Fracture and Fatigue mechanics (macroscale)

We are performing several mechanical tests to characterize the material behaviour. We are particularly interested in performing in-situ SEM toughness tests as well as fatigue tests. Fracture toughness tests provide the resistance to fracture at each increment of stable crack extension (R-curve). Fatigue tests provide the resistance to initiation and propagation of cracks resulting from cyclic loading, allowing to calculate the fatigue life or fatigue strength (Paris law, S-N curve) of the material. Both mechanical properties, associated with monotonic or cyclic loading, have shown to be impaired with bone fragility.

 

Microscopic constituents (microscale)

Some of the most important crack resistance qualities of cortical bone occur at the micrometer length-scale. We are characterizing them using Synchrotron Radiation X-ray Micro-Tomography (SRuT). This technique provides 3D structural information at micron level such as size of osteon’s Haversian canal and osteocyte lacunae. Following mechanical testing, a 3D image of crack growth from a notch can also be visualize. Using this technique, we investigate how biological changes caused by age, disease, treatment, etc. affect the microstructural features and their interaction with the crack growth, and in turn, how these factors alter the fracture resistance.

 

Collagen and mineral deformation (nanoscale)

At this nanometer length-scale, bone’s basic building blocks mineralized collagen fibrils. At this scale, bone acquires its unique combination of strength and toughness through composite deformation of the strong hydroxyapatite (HA) crystals and tough collagen. To study deformation at the collagen fibrillar and mineral scales, we are performing small- and wide-angle x-ray scattering/diffraction (SAXS/WAXD) experiments with simultaneous mechanical testing. Using this technique, we elucidate how ultrastructural changes induced by bone fragility alter the load transfer mechanism from the tissue to the smallest particle level.

 

Role of osteocyte

Osteocyte cells are comprising 90% of the bone cell population and are major coordinators of bone remodelling. Embedded within the bone matrix, osteocytes have the ability to sense stress and deformation, and respond to them by signaling neighbouring osteoblast and osteoclast cells. Indeed, they are thought to have a central role in microdamage and crack repair. Osteocyte-mediated perilacunar remodelling plays an essential role in the biological control of bone quality. Yet to which extent osteocytes are affecting bone quality through mineralization, collagen deformation, and lacunar geometry changes remains an area of active investigation.