A deeper understanding of the cartilage-bone mechanics is fundamental to unravel onset and progression of osteoarthritis, enabling better diagnosis and treatment. The aim of this study is therefore to explore the capability of X-ray computed (XCT) phase-contrast imaging in a lab-based system to enable digital volume correlation (DVC) measurements of unstained cartilage-bone plugs from healthy adult bovines. DVC strain uncertainties were computed for both articular cartilage and mineralized tissue (calcified cartilage and subchondral bone) in the specimens at increasing propagation distances, ranging from absorption up to four times (4× such effective distance. In addition, a process of dehydration and rehydration was proposed to improve feature recognition in XCT of articular cartilage and mechanical properties of this tissue during the process were assessed via micromechanical probing (indentation), which was also used to determine the effect of long X-ray exposure. Finally, full-field strain from DVC was computed to quantify residual strain distribution at the cartilage-bone interface following unconfined compression test (ex situ). It was found that enhanced gray-scale feature recognition at the cartilage-bone interface was achieved using phase-contrast, resulting in reduced DVC strain uncertainties compared to absorption. Residual strains up to ~7000 µε in the articular cartilage were transferred to subchondral bone via the calcified cartilage and micromechanics revealed the predominant effect of long phase-contrast X-ray exposure in reducing both stiffness and hardness of the articular cartilage. The results of this study will pave the way for further development and refinement of the techniques, improving XCT-based strain measurements in cartilage-bone and other soft-hard tissue interfaces.

Retinopathy of prematurity, formerly known as a retrolental fibroplasia, is a leading cause of infantile blindness worldwide. Retinopathy of prematurity is caused by the failure of central retinal vessels to reach the retinal periphery, creating a nonperfused peripheral retina, resulting in retinal hypoxia, neovascularization, vitreous hemorrhage, vitreoretinal fibrosis, and loss of vision. We established a potential retinopathy of prematurity model by using a green fluorescent vascular endothelium zebrafish transgenic line treated with cobalt chloride (a hypoxia-inducing agent), followed by GS4012 (a vascular endothelial growth factor inducer) at 24 hours postfertilization, and observed that the number of vascular branches and sprouts significantly increased in the central retinal vascular trunks 2–4 days after treatment. We created an angiography method by using tetramethylrhodamine dextran, which exhibited severe vascular leakage through the vessel wall into the surrounding retinal tissues. The quantification of mRNA extracted from the heads of the larvae by using real-time quantitative polymerase chain reaction revealed a twofold increase in vegfaa and vegfr2 expression compared with the control group, indicating increased vascular endothelial growth factor signaling in the hypoxic condition. In addition, we demonstrated that the hypoxic insult could be effectively rescued by several antivascular endothelial growth factor agents such as SU5416, bevacizumab, and ranibizumab. In conclusion, we provide a simple, highly reproducible, and clinically relevant retinopathy of prematurity model based on zebrafish embryos; this model may serve as a useful platform for clarifying the mechanisms of human retinopathy of prematurity and its progression.

The mechanical and tribological characteristics of thin chromium oxide films are investigated by controlling the process parameters in reactive deposition and subsequent annealing. From this, the correlation between the deposition process, film structure, and properties is established. Substrate heating and oxygen partial pressure are found to be the critical parameters that alter the oxygen concentration and crystallization of the films which, in turn, affect their stress, hardness, and wear resistance. The chromium oxide film deposited at 150 °C in pure argon and annealed at 300 °C shows a hardness of 25 GPa, which is near the bulk hardness of Cr2O3, and exhibits a good wear resistance with adhesive wear being the dominant wear mechanism. Reactive deposition at 25 °C or with excessive oxygen leads to films with nonstoichiometric composition, which hinders their crystallization upon low-temperature annealing. As a result, the hardness is reduced, and the wear resistance deteriorates several orders of magnitude with a concomitant transition of the wear mechanism from adhesive into an abrasive regime.

Repair of ligaments and tendons requires scaffolds mimicking the spatial organisation of collagen in the natural tissue. Electrospinning is a promising technique to produce nanofibres of both resorbable and biostable polymers with desired structural and morphological features. The aim of this study was to perform high-resolution x-ray tomography (XCT) scans of bundles of Nylon6.6, pure PLLA and PLLA-Collagen blends, where the nanofibres were meant to have a predominant direction. Characterisation was carried out via a dedicated methodology to firmly hold the specimen during the scan and a workflow to quantify the directionality of the nanofibres in the bundle. XCT scans with 0.4 and 1.0 μm voxel size were successfully collected for all bundle compositions. Better image quality was achieved for those bundles formed by thicker nanofibres (i.e. 0.59 μm for pure PLLA), whereas partial volume effect was more pronounced for thinner nanofibres (i.e. 0.26 μm for Nylon6.6). As expected, the nanofibres had a predominant orientation along the axis of the bundles (more than 20% of the nanofibres within 3° and more than 60% within 18° from the bundle axis), with a Gaussian-like dispersion in the other directions. The directionality assessment was validated by comparison against a similar analysis performed on SEM images: the XCT analysis overestimated the amount of nanofibres very close to the bundle axis, especially for the materials with thinnest nanofibres, but adequately identified the amount of nanofibres within 12°. LAY DESCRIPTION: Repair of ligaments and tendons requires dedicated materials (scaffolds) mimicking the spatial organisation of the collagen (the main material composing such natural tissue). Electrospinning is a promising technique that allows production of fibres with nanometric dimension using high voltage to stretch very tiny drops of polymeric solutions. Electrospinning allows processing both polymers that can be resorbed by the host tissue, and nonresorbable ones, to obtain the desired structural and morphological features by arranging the nanofibres in bundles. The aim of this study was to perform high-resolution x-ray computed tomography (XCT) scans of bundles, where the nanofibres were meant to have a predominant direction. The investigation included bundles of different compositions: a biostable polymer (Nylon) and bioresorbable ones (pure Poly-L-lactic acid (PLLA) and PLLA-Collagen blends). The electrospun bundles were produced using a validated method (Sensini et al 2017: https://doi.org/10.1088/1758-5090/aa6204). To this end, we developed a dedicated methodology to scan such small specimens, and a workflow to quantify the directionality of the nanofibres in the bundle. For all the compositions, XCT scans with extremely high resolution (i.e. down to 0.4 μm) were successfully collected. As expected, better images were obtained for those bundles where the nanofibres were thicker than the scanning resolution (i.e. 0.59 μm for pure PLLA). The images of the thinnest nanofibres (i.e. 0.26 μm for Nylon)...

The effect of low-energy ion bombardment on the structure and properties of zirconia films deposited by reactive ion-beam process is investigated. Bombardment of 100-eV Ar+ during film growth is shown to induce a substantial relaxation of the residual stress as a result of structural modification by the increased mobility of adatoms. Concurrently, the oxygen gettering capability, or film stoichiometry, is improved by the enhanced diffusion of oxygen on substrate surface. The structural change by thermal annealing, up to 600 °C, demonstrates that fine-grained (200–400 Å) cubic zirconia can be stabilized down to room temperature without alloying stabilizers. The impingement of low-energy Ar+ during film growth results in an as-deposited film microstructure which promotes the growth of the cubic-phase crystallites upon post-deposition annealing as well as the texturing of film plane into (111) orientation. The refractive index and optical transmission of the zirconia films are shown to be dependent predominantly upon the oxygen content in the film and less sensitive to the improved atomic packing due to the low-energy Ar+ bombardment.

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Void formation in tensile test under hydrostatic pressure is characterized through quantitative metallography, and the fracture mechanism under pressure is analyzed by fractography. Transition of the fracture surface from the cup-and-cone under atmospheric pressure to a slant structure under high pressure is explained on the basis of the void development leading to fracture and the concomitant change in fracture mechanism. The concept of "shear blocks" is introduced to illustrate the features observed on the fracture surface of specimens tested under high pressure. It is postulated that shear blocks evolve to connect the central crack regions with the shear crack initiated on neck surface due to the severe necking deformation under applied pressure.

The mechanical behaviour of regenerated bone tissue during fracture healing is key in determining its ability to withstand physiological loads. However, the strain distribution in the newly formed tissue and how this influences the way a fracture heals it is still unclear. X-ray Computed Tomography (XCT) has been extensively used to assess the progress of mineralised tissues in regeneration and when combined with in situ mechanics and digital volume correlation (DVC) has been proven a powerful tool to understand the mechanical behaviour and full-field three-dimensional (3D) strain distribution in bone. The purpose of this study is therefore to use in situ XCT mechanics and DVC to investigate the strain distribution and load-bearing capacity in a regenerating fracture in the diaphyseal bone, using a rodent femoral fracture model stabilised by external fixation. Rat femurs with 1 mm and 2 mm osteotomy gaps were tested under in situ XCT stepwise compression in the apparent elastic region. High strain was present in the newly formed bone (ε p1 and ε p3 reaching 29 000 µε and -43 000 µε, respectively), with a wide variation and inhomogeneity of the 3D strain distribution in the regenerating tissues of the fracture gap, which is directly related to the presence of unmineralised tissue observed in histological images. The outcomes of this study will contribute in understanding natural regenerative ability of bone and its mechanical behaviour under loading.