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Yde Pedersen posted an update 6 months, 2 weeks ago
Compressive tests were carried out to estimate the elastic modulus of the produced structures and finite element analyses were performed, for comparison purposes. Linear correlations were found for the dimensions, porosity, and elastic modulus when comparing the CAD design with the SLM structures. The produced NiTi structures exhibit elastic moduli that match that of bone tissue, which is a good indication of the potential of these structures in orthopaedic implants.Magnetic resonance imaging (MRI) under mechanical loading, commonly referred to as stress MRI, allows the evaluation of functional properties of intra- and periarticular tissues non-invasively beyond static assessment. Quantitative MRI can identify physiological and pathological responses to loading as indication of, potentially treatable, early degeneration and load transmission failure. Therefore, we have developed and validated an MRI-compatible pressure-controlled axial loading device to compress human knee specimens under variable loading intensity and axis deviation. Ten structurally intact human knee specimens (mean age 83.2 years) were studied on a 3.0T scanner (Achieva, Philips). Proton density-weighted fat-saturated turbo spin-echo and high-resolution 3D water selective 3D gradient-echo MRI scans were acquired sequentially at 10° joint flexion in seven configurations unloaded and then at approximately half and full body weight loading in neutral, 10° varus and 10° valgus alignment, respectively. Following manual segmentation in both femorotibial compartments, cartilage thickness (ThC) was determined as well as meniscus extrusion (ExM). These measures were compared to computed tomography scans, histological grading (Mankin and Pauli scores), and biomechanical properties (Instantaneous Young’s Modulus). Compartmental, regional and subregional changes in ThC and ExM were reflective of loading intensity and joint alignment, with the greatest changes observed in the medial compartment during varus and in the lateral compartment during valgus loading. These were not significantly associated with the histological tissue status or biomechanical properties. In conclusion, this study explores the physiological in-situ response of knee cartilage and meniscus, based on stress MRI, and as a function of loading intensity, joint alignment, histological tissue status, and biomechanical properties, as another step towards clinical implementation.Aponeuroses are stiff sheath-like components of the muscle-tendon unit that play a vital role in force transmission and thus locomotion. There is clear importance of the aponeurosis in musculoskeletal function, but there have been relatively few studies of aponeurosis material properties to date. The goals of this work were to 1) perform tensile stress-relaxation tests, 2) perform planar biaxial tests, 3) employ computational modeling to the data from 1 to 2, and 4) perform scanning electron microscopy to determine collagen fibril organization for aponeurosis tissue. Viscoelastic modeling and statistical analysis of stress-relaxation data showed that while relaxation rate differed statistically between strain levels (p = 0.044), functionally the relaxation behavior was nearly the same. Biaxial testing and associated modeling highlighted the nonlinear (toe region of ~2-3% strain) and anisotropic (longitudinal direction linear modulus ~50 MPa, transverse ~2.5 MPa) tensile mechanical behavior of aponeurosis tissue. Comparisons of various constitutive formulations showed that a transversely isotropic Ogden approach balanced strong fitting (goodness of fit 0.984) with a limited number of parameters (five), while damage modeling parameters were also provided. Scanning electron microscopy showed a composite structure of highly aligned, partially wavy collagen fibrils with more random collagen cables for aponeurosis microstructure. Future work to expand microstructural analysis and use these data to inform computational modeling would benefit this work and the field.In order to understand the fracture toughness anisotropy of avian eggshells, we have investigated eggshells of the emu (Dromaius novaehollandiae) whereby the large size (~13 cm × 9.5 cm) enabled the fabrication of beam samples in various orientations. The emu eggshell was found to have a hierarchical microstructure similar to chicken eggshell, with the only significant difference being the absence of a continuous cuticle layer. Emu eggshell was found to have significantly lower strength when samples were tested in the outwards direction (i.e., a crack initiates on the inside of the shell and propagates towards the outer surface) as compared to the inwards testing direction. Furthermore, samples that were oriented parallel to the egg axis (i.e., the longitudinal direction) and tested inwards showed higher strength, ~24 MPa, compared to the samples that were made from the latitudinal orientation, ~20 MPa. Independent of orientation, the outwards testing direction resulted in strength values of ~15 MPa. The fracture toughness of the emu eggshell for cracking in the circumferential direction was ~0.3 MPa√m, independent of sample orientation, and this value was comparable to the fracture toughness of chicken eggshell tested in the same orientation. In the radial outwards direction, however, the fracture toughness was ~80% lower (~0.06 MPa√m) than in the circumferential direction. The low fracture toughness for this orientation was associated with the separation of the highly oriented calcite crystals in the mammillary cone layer of the eggshell structure which is easier compared to calcite crystal fracture. The large anisotropy in fracture toughness is thought to allow for easy escape of the chick while simultaneously protecting the embryo during development.All levels of the unique hierarchical structure of bone, consisting of collagen and hydroxyapatite crystals at the nanoscale to osteon/lamellae structures at the microscale, contribute to its characteristic toughness and material properties. Elements of bone’s density and size contribute to bone quantity (or bone mass), whereas elements of bone’s material composition, material properties, internal structure, and organization describe bone quality. BAY-3605349 solubility dmso Bone quantity and quality can be degraded by factors such as aging, disease, treatments, and irradiation, compromising its ability to resist fracture and sustain loading. Accessing the morphology and architecture of bone at the microscale to quantify microstructural features and assess the degree of mineralization and path of crack propagation in bone provides crucial information on how these factors are influencing bone quantity and quality. Synchrotron radiation micro-computed tomography (SRμCT) was first used to assess bone structure at the end of the 1990’s. One of the main advantages of the technique is that it enables accurate three-dimensional (3D), non-destructive quantification of structure while traditional histomorphometry on histological sections is inherantly destructive to the sample and two-dimensional (2D).