RESEARCH
Our research is bridging the gap between fracture mechanics, material characterization, and biology. We aim to investigate the structure, fracture 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 millimeter length-scales, we investigate their hierarchical structure, deformation/fracture mechanisms, and biological activities using advanced x-ray synchrotron instrumentation designed to capture behavior at multiple dimensions. We connect phenomena at molecular and micrometer length-scales to macroscale, whole bone properties using macroscale mechanical testing (strength, toughness and fatigue tests).
Using this multi-scale experimental approach, we have explored highly diverse biosamples, including bone from human and animal models, intervertebral discs, fish scales, skin, mantis shrimp telson, and more. In addition to a diverse collection of biosamples, the F² Lab also investigates bone fragility associated with a wide variety of diseases (osteonecrosis, diabetes, osteoporosis, osteogenesis imperfecta), treatments (bisphosphonate and corticosteroid), as well as fatigue loading. This work provides 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 scientific discovery. In the F² Lab, synchrotron techniques are key for investigating smaller length scales (micro- to nanoscale). Synchrotron radiation micro-computed tomography (SRuT) allows us to study microstructural features and mineral composition at the micro-scale via high-resolution image data. Small- and wide-angle x-ray scattering/diffraction (SAXS/WAXD) experiments allow us to examine spacing of bone’s most basic constituent, collagen, at the nanoscale.
Keywords: stress and fatigue fracture mechanics, skeletal biomechanics, bone quality and bone fragility, synchrotron radiation micro-tomography, synchrotron radiation x-ray scattering
Fracture and Fatigue mechanics (macroscale)
We are performing several mechanical tests to characterize the material behavior. 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 micro-computed 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 neighboring 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.
Image Processing and Deep Learning
Synchrotron radiation micro-computed tomography (SRuT) provides unprecedented access to the internal morphology of bone. When combined with
in situ mechanical testing, this imaging technique can reveal the nature of crack propagation in bone in near-real time. We use
in situ SRuT mechanical testing to study how a crack traveling through bone interacts with features, such as canals, within the bone. In order to process image data obtained from these tests, we use deep convolutional neural networks to perform denoising and segmentation. In the image to the left, the gray represents bone mineral tissue, the pink represents a crack that has grown through the bone during testing, and the blue represents the canals which transport nutrients through the bone.
