We propose an experimental technique for the estimation of quality parameters of post-mortem human bone samples with signs of osteoporosis. Since we were interested in characterizing bone microstructure by evaluating porosity, trabecular thickness, and space, we obtained reference values of those parameters for some of our samples through micro-computerized tomography (micro-CT). Nevertheless, as such technology is not widely available, here we used a 2D imaging approximation of those quality parameters. We based our estimation on simple digital microscopy and calibrated to ensure a percentage of similarity higher than 95% in comparison to those values achieved through micro-CT. Additionally, we subjected our samples to mechanical testing to obtain a complete characterization of our samples and to provide a preliminary assessment of the possible relationship between clinical tests of bone mineral density (BMD) and bone quality parameters. Our results show that BMD may have very low specificity in the assessment of the authentic microstructure of bone, then a broader analysis of quality parameters is required to enhance the reliability of future osteoporosis diagnosis technologies.
We have proposed a new model for microcrack detection by osteocytes in bone. According to this model, cell signalling is initiated by the cutting of cellular processes which span the crack. We show that shear displacements of the crack faces are needed to rupture these processes, in an action similar to that of a pair of scissors. Current work involves a combination of cell biology experiments, theoretical and experimental fracture mechanics and system modelling using control theory approaches. The approach will be useful for understanding effects of extreme loading, aging, disease states and drug treatments on bone damage and repair; the present paper presents recent results from experiments and simulations as part of current, ongoing research.
Cobalt-based alloys are widely used in the manufacture of joint prostheses. In this study, the effect of boron additions and heat treatment on the ASTM F75 was evaluated by rotating bending fatigue. The boron ranged from 0.06–1 wt %. The alloys were tested in as-cast and heat-treated conditions. In the as-cast condition, the infinite life was observed at 380 MPa, improving to 433–615 MPa according to the amount of boron added. In the heat treatment condition, the fatigue resistance was improved only in the base alloy. The addition of 0.06 wt % boron and heat treatment led to the same resistance as in the as-cast condition. Adding large amounts of boron combined with heat treatment diminished the fatigue limit. The fracture analysis revealed primarily brittle behaviour with some ductile features even on the same sample; only the heat-treated alloy with 0.06 wt % boron was clearly ductile. This alloy also exhibited notably better toughness to crack propagation.
A clear understanding of the dependence of mechanical properties of bone remains a task not fully achieved. In order to estimate the mechanical properties in bones for implants, pore cross-section area, calcium content, and apparent density were measured in trabecular bone samples for human implants. Samples of fresh and defatted bone tissue, extracted from one year old bovines, were cut in longitudinal and transversal orientation of the trabeculae. Pore cross-section area was measured with an image analyzer. Compression tests were conducted into rectangular prisms. Elastic modulus presents a linear tendency as a function of pore cross-section area, calcium content and apparent density regardless of the trabecular orientation. The best variable to estimate elastic modulus of trabecular bone for implants was pore cross-section area, and affirmations to consider Nukbone process appropriated for marrow extraction in trabecular bone for implantation purposes are proposed, according to bone mechanical properties. Considering stress-strain curves, defatted bone is stiffer than fresh bone. Number of pores against pore cross-section area present an exponential decay, consistent for all the samples. These graphs also are useful to predict elastic properties of trabecular samples of young bovines for implants.
We work in the consolidation of previous studies performed by us concerning microdamage developments in bones with use of conventional basic fuchsin staining, in which we stated that age and gamma radiation had a direct influence on the increase in the generation and growth of microfractures, to provoke the fracture of bones by fatigue by means of a novel theoretical model based on a concept called characteristic length. The mentioned conventional staining technique has the disadvantage of being invasive, destructive, two-dimensional (2-D), and tedious. For this reason, the aim of our current work was the use of a world-unique patented computed tomography device – TORATOM. With the use of precipitation barium sulfate process, we identified individual microcracks, which will be analysed in further studies to define better predictive models to understand and prevent fatigue fractures due to stress and fragility related to osteoporosis, which will be useful in developing new clinical approaches to the problem of osteoporosis.
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