Bone toughness and crack propagation: An experimental study

Bone is a topic of great interest for researchers, such as biologists or engineers, both interested in understanding the structurerelated properties of bone and how they are affected by aging, disease and therapies. In particular, a topic of common interest between medicine and engineering is the fracture behavior of bone. Indeed, a thorough understanding of the mechanical behavior of bone is helpful to predict the fracture risk, but it can also provide the basis for the design of de novo biomimetic materials. In this paper, we show the initial results of an experimental study of the mechanical behavior of bovine bone, with a special focus on fracture toughness. The latter is evaluated under tensile and bending loading, by following the ASTM adopted for metals. Finally, we perform microscopic observations to better understand the fracture behavior and correlate it with the microscopic structure

Understanding the structure-property relationship in cortical bone to design a biomimetic composite

Bone is a hot topic for researchers, interested in understanding the structure-related properties of the tissue and the effect of aging, disease and therapies on that. A thorough understanding of the mechanical behavior of bone can be helpful to medical doctors to predict the fracture risk, but it can also serve as a guideline for engineers for the design of de novo biomimetic materials. In this paper, we show a complete characterization of cortical bone under static loading (i.e. tensile, compressive, three-point bending) and we carried out tests in presence of a crack to determine the fracture toughness. We performed all the tests on wet samples of cortical bone, taken from bovine femurs, by following the ASTM standards designed for metals and plastics. We also performed microscopic observations, to get an insight into the structure-property relationship. We noted that the mechanical response of bone is strictly related to the microstructure, which varies depending on the anatomical position. This confirms that the structure of bone is optimized, by nature, to withstand the different types of loads generally occurring in different body areas. The same approach could be followed for a proper biomimetic design of new composites

Fatigue behaviour of a GFRP laminate by thermographic measurements

Composite materials are widely used to build structural components, thanks to their mechanical properties. Those are generally considered ‘engineering materials’, since they are tailored to meet specific requirements. Due to their use for structural components, it is important to know their mechanical behaviour, especially under cyclic loads. At present, there is a common interest, among researchers, to study the mechanical behaviour of composites, by means of both traditional and innovative techniques, with the final purpose of making previsions regarding their service life. In fact, due to their composite nature, they behave in a different mode compared to homogeneous materials. This study is focused on a glass fibre-reinforced plastic (GFRP); the aim of this work is to study its fatigue behaviour, from both the mechanical and the thermal points of view. The main reason is that there is a lack of knowledge, in the literature, about the fatigue of composites. In this study, a GFR laminate was characterized under static and dynamic loading conditions; during the experimental tests, thermal measurements were carried out by means of an IR-thermal camera. Temperature measurements were done during the static tests, whereas in the dynamic tests the dissipated energy was measured, by using the dissipation method (D-mode). Then, various criteria for fatigue life estimation were applied fitting the experimental data. Since different thermographic techniques have been used to estimate the fatigue behaviour, a final comparison between the experimental data and the predicted fatigue behaviour is proposed and discussed, showing a good agreement

Crumpling-based soft metamaterials: The effects of sheet pore size and porosity

Crumpled-based materials are relatively easy to fabricate and show robust mechanical properties for practical applications, including meta-biomaterials design aimed for improved tissue regeneration. For such requests, however, the structure needs to be porous. We introduce a crumpled holey thin sheet as a robust bio-metamaterial and measure the mechanical response of a crumpled holey thin Mylar sheet as a function of the hole size and hole area fraction. We also study the formation of patterns of crease lines and ridges. The area fraction largely dominated the crumpling mechanism. We also show, the crumpling exponents slightly increases with increasing the hole area fraction and the total perimeter of the holes. Finally, hole edges were found to limit and guide the propagation of crease lines and ridges

Isolating the Role of Bone Lacunar Morphology on Static and Fatigue Fracture Progression through Numerical Simulations

Currently, the onset of bone damage and the interaction of cracks with the surrounding micro-architecture are still black boxes. With the motivation to address this issue, our research targets isolating lacunar morphological and densitometric effects on crack advancement under both static and cyclic loading conditions by implementing static extended finite element models (XFEM) and fatigue analyses. The effect of lacunar pathological alterations on damage initiation and progression is evaluated; the results indicate that high lacunar density considerably reduces the mechanical strength of the specimens, resulting as the most influencing parameter among the studied ones. Lacunar size has a lower effect on mechanical strength, reducing it by 2%. Additionally, specific lacunar alignments play a key role in deviating the crack path, eventually slowing its progression. This could shed some light on evaluating the effects of lacunar alterations on fracture evolution in the presence of pathologies

Hydrogen embrittlement behavior in FeCCrNiBSi TRIP steel

The effect of plastic deformations on the hydrogen embrittlement (HE) of transformation-induced plasticity (TRIP) steel was studied. In situ tensile tests showed that with increasing hydrogen current density, total elongation loss was raised to 36.8% as compared to an uncharged specimen. The electron backscatter diffraction (EBSD) observation indicated that hydrogen charging decreased stacking fault energy (SFE), resulting in the formation of more α′- martensite by both indirect and direct transformation. The α′- martensite volume fraction at the same degree of deformation in uncharged and charged samples was 31% and 39%, respectively. With plastic deformation, reversible trap sites were raised because of the increased dislocation density and the formation of α′- martensite, which was obtained from EBSD characterization and had a good correlation with the results of the thermal desorption spectroscopy (TDS) analysis

Investigation of the Effect of Internal Pores Distribution on the Elastic Properties of Closed-Cell Aluminum Foam: A Comparison with Cancellous Bone

Closed-cell aluminum foams belong to the class of cellular solid materials, which have wide application in automotive and aerospace industries. Improving the mechanical properties and modifying the manufacturing process of such materials is always on demand. It has been shown that the mechanical properties of cellular materials are highly depending on geometrical arrangement, mechanical properties of solid constituents and the relative density of these materials. In this study, using a manufacturing process of foaming by expansion of a blowing agent, we prepared two types of closed-cell aluminum foams with isotropic distribution of cells along length and foams with gradient of pores along its length. We hypothesized that such variation of pores can induce microstructural directionality along the length of foam samples and improve their mechanical properties. For this aim, we studied the microstructural properties by micro-CT imaging and found their relation to macroscopic mechanical properties of foam samples by conducting monotonic compression tests. We compared these results with the one of the bovine femur trabecular bone as they show a dominant microstructural anisotropy due to alignment with the maximum strength direction in body. We also conducted numerical analyses and validated them for the elastic part based on our experimental work. Our results showed that gradient variation in porosity in closed-cell aluminum foams have a minor effect on their macroscopic mechanical properties. Although using such materials in sandwich panel structures, the strength of the material slightly increased. In addition, parameters of a power law model for the description of mechanical properties of foam sample and their relative density and properties of the solid compartment were characterized. The presented results are considered as a preliminary study for improvement of mechanical properties of closed-cell aluminum foams

Patients' health locus of control and preferences about the role that they want to play in the medical decision-making process

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Respiratory function in cybrid cell lines carrying European mtDNA haplogroups: implications for Leber's hereditary optic neuropathy

AbstractThe possibility that some combinations of mtDNA polymorphisms, previously associated with Leber's hereditary optic neuropathy (LHON), may affect mitochondrial respiratory function was tested in osteosarcoma-derived transmitochondrial cytoplasmic hybrids (cybrids). In this cellular system, in the presence of the same nuclear background, different exogenous mtDNAs are used to repopulate a parental cell line previously devoid of its original mtDNA. No detectable differences in multiple parameters exploring respiratory function were observed when mtDNAs belonging to European haplogroups X, H, T and J were used. Different possible explanations for the previously established association between haplogroup J and LHON 11778/ND4 and 14484/ND6 pathogenic mutations are discussed, including the unconventional proposal that mtDNA haplogroup J may exert a protective rather than detrimental effect

Rational design of soft mechanical metamaterials: Independent tailoring of elastic properties with randomness

The elastic properties of mechanical metamaterials are direct functions of their topological designs. Rational design approaches based on computational models could, therefore, be used to devise topological designs that result in the desired properties. It is of particular importance to independently tailor the elastic modulus and Poisson's ratio of metamaterials. Here, we present patterned randomness as a strategy for independent tailoring of both properties. Soft mechanical metamaterials incorporating various types of patterned randomness were fabricated using an indirect additive manufacturing technique and mechanically tested. Computational models were also developed to predict the topology-property relationship in a wide range of proposed topologies. The results of this study show that patterned randomness allows for independent tailoring of the elastic properties and covering a broad area of the elastic modulus-Poisson's ratio plane. The uniform and homogenous topologies constitute the boundaries of the covered area, while topological designs with patterned randomness fill the enclosed area