1,721,463 research outputs found
Understanding the structure-property relationship in cortical bone to design a biomimetic composite
Full text linkBone 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
The lipid lowering effects of iodothyronines: in vivo and in vitro studies on rat liver
No full textNon-alcoholic fatty liver disease (NAFLD) is emerging as one of the most common liver diseases, leading to the increasing interest for new therapeutic approaches for its treatment. NAFLD primarily depends on a hypercaloric and/or unbalanced diet leading to overweight and obesity. The liver, in fact, plays a central role in lipid metabolism by importing free fatty acids from the blood and synthesizing, storing, oxidizing and exporting lipids. Furthermore, the liver is the target for the thyroid hormones, thyroxine (T4) and 3,3',5-triiodo-L-thyronine (T3), that stimulate the basal metabolic rate and lead to body weight loss. In the last decade, other iodothyronines have been shown to possess biological relevance and play some thyromimetic activities; in particular, 3,5-diiodo-L-thyronine (T2) gained large interest. The global effect of iodothyronines on liver lipid metabolism results from the balance between direct and indirect actions on the hepatocyte, leading to stimulation of lipid synthesis, oxidation and autophagy. In this review, the results so far obtained on both in vivo and in vitro models of hepatosteatosis are summarized in order to obtain an updated picture of the lipid-lowering effects of iodothyronines on mammalian live
Crack Propagation in Cortical Bone: A Numerical Study
Full text linkThe fracture behavior of human bone is an interesting field of research for medical scientists, which are interested in predicting the fracture risk, but also for engineers, which are interested in mimicking bone structure in the design of new materials. To understand this phenomenon and to be able to make predictions, many numerical techniques are currently adopted, with the goal of reaching different length scales. In this paper we present a numerical study of the microstructure of human bone, via a cohesive-based X-FEM approach. A single osteon model is developed to investigate the mechanisms of crack propagation and the role played by the mechanical properties of the micro-structural constituents, and in particular by the cement line. The latter has shown to strongly affect the crack path, by acting as a barrier and arresting or preventing a continuous crack propagation, and causing a deviation, leading to an increase in the fracture energy
Bone toughness and crack propagation: An experimental study
Full text linkBone 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
Fatty Acids and Effects on In Vitro and In Vivo Models of Liver Steatosis
No full textBackground:Fatty liver, or steatosis, is a condition of excess accumulation of lipids, mainly under form of triglycerides (TG), in the liver, and it is the hallmark of non-alcoholic fatty liver disease (NAFLD). NAFLD is the most common liver disorder world-wide and it has frequently been associated with obesity, hyperlipidemia and insulin resistance. Free fatty acids (FA) are the major mediators of hepatic steatosis; patients with NAFLD have elevated levels of circulating FA that correlate with disease severity.Methods:Steatosis is a reversible condition that can be resolved with changed behaviors, or that can progress towards more severe liver damages such as steatohepatitis (NASH), fibrosis and cirrhosis. In NAFLD, FA of exogenous or endogenous origin accumulate in the hepatocytes and trigger liver damages. Excess TG are stored in cytosolic lipid droplets (LDs) that are dynamic organelles acting as hubs for lipid metabolism.Results:In the first part of this review, we briefly reassumed the main classes of FA and their chemical classification as a function of the presence and number of double bonds, their metabolic pathways and effects on human health. Then, we summarized the main genetic and diet-induced animal models of NAFLD, as well as the cellular models of NAFLD.Conclusions:In recent years, both the diet-induced animal models of NAFLD as well as the cellular models of NAFLD have found ever more application to investigate the mechanisms involved in NAFLD, and we referred to their advantages and disadvantages.</jats:sec
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