Search for: All records

Not AvailaMineral imbalances in the body from chronic kidney disease can impact bone turnover and cause cortical bone loss. Synthetic salmon calcitonin is an FDA-approved treatment for bone fragility observed in diseases such as osteoporosis, and clinical trials have demonstrated a reduction in fractures compared to untreated individuals. This study documents the effects of calcitonin on cortical bone using an in vivo mouse model of chronic kidney disease. Serum BUN and PTH are reported. Calcitonin was found to impact at a dose of 50/IU/kg/day five times a week for five weeks. MicroCT was used to evaluate bone quantity measures, such as cortical porosity, thickness, bone area, and long bone structural geometric parameters. It was found that porosity, thickness, and bone geometry are affected by disease, but not by treatment at the specified regime. Small and wide-angle x-ray scattering (SAXS and WAXS) was used to obtain the nanostructure of the mineral-collagen-water composite, including mineral dimensions, -periodicity and collagen spacing. Data from thermogravimetric analysis (TgA) were used to quantify wt.% of the mineral, collagen, and bound water of each sample. Chronic kidney disease was found to decrease collagen spacing to increase mineral weight fractions, and to reduce loosely bound water. There were no changes from chronic kidney disease on the -Periodicity. Treatment increased the weight percent of collagen, with no effect on other bone quality parameters. 

Quasi-brittle fracture mechanics is used to evaluate fracture of human cortical bone in aging. The approach is demonstrated using cortical bone bars extracted from one 92-year-old human male cadaver. In-situ fracture mechanics experiments in a 3D X-ray microscope are conducted. The evolution of the fracture process zone is documented. Fully developed fracture process zone lengths at peak load are found to span about three osteon diameters. Crack deflection and arrest at cement lines is a key process to build extrinsic toughness. Strength and toughness are found as size-dependent, not only for laboratory-scale experimental specimens but also for the whole femur. A scaling law for the length fracture process zone is used. Then, size-independent, tissue fracture properties are calculated. Linear elastic fracture mechanics applied to laboratory beam specimens underestimates the tissue toughness by 60%. Tissue fracture properties are used to predict the load capacity of the femur in bending within the range of documented data. The quasi-brittle fracture mechanics approach allows for the assessment of the combined effect of bone quantity and bone quality on fracture risk. However, further work is needed considering a larger range of subjects and in the model validation at the organ length scale. 

Abstract The present study is concerned with the deformation response of an architectured material system, i.e., a 2D-material system created by the topological interlocking assembly of polyhedra. Following the analogy of granular crystals, the internal load transfer is considered along well-defined force networks, and internal equivalent truss structures are used to describe the deformation response. Closed-form relationships for stiffness, strength, and toughness of the topologically interlocked material system are presented. The model is validated relative to direct numerical simulation results. The topologically interlocked material system characteristics are compared with those of monolithic plates. The architectured material system outperforms equivalent size monolithic plates in terms of toughness for nearly all possible ratios of modulus to the strength of the material used to make the building blocks and plate, respectively. In addition, topologically interlocked material systems are shown to provide better strength characteristics than a monolithic system for low strength solids. 

Topologically interlocked stereotomic material systems are load-carrying assemblies of unit elements interacting by contact and friction. This contribution summarizes research on such material systems in a variety of configurations based on tessellation geometry and percolation, and it considers external rigid confined, external flexible confined, internal flexible confined, as well as considers the unit elements as solids (elastic and elastic-brittle) or shells (elastic), and under consideration of a range of assembly geometries. Siegmund, T. (2018). Topologically Interlocked Material Systems: From a Material Design Concept to Properties. In T. Siegmund & F. Barthelat (Eds.) Proceedings of the IUTAM Symposium Architectured Materials Mechanics, September 17-19, 2018, Chicago, IL: Purdue University Libraries Scholarly Publishing Services, 2018. https://docs.lib.purdue.edu/iutam/presentations/abstracts/70 

This publication contains a finite element model for the analysis of single bone trabeculae under consideration of bone tissue heterogeneity and tissue anisotropy. The model for bone tissue heterogeneity and anisotropy follows: Hammond, M.A., Wallace, J.M., Allen, M.R. and Siegmund, T., 2018. Incorporating tissue anisotropy and heterogeneity in finite element models of trabecular bone altered predicted local stress distributions. Biomechanics and Modeling in Mechanobiology, 17(2), pp.605-614. In this publication the finite element model, material set assignment and local orientations are provided. This dataset contains an inp file in the syntax of Abaqus/Standard software v2017. 

This publication contains a finite element model for the analysis of bone core under consideration of bone tissue heterogeneity and tissue anisotropy. The model for bone tissue heterogeneity and anisotropy follows: Hammond, M.A., Wallace, J.M., Allen, M.R. and Siegmund, T., 2018. Incorporating tissue anisotropy and heterogeneity in finite element models of trabecular bone altered predicted local stress distributions. Biomechanics and Modeling in Mechanobiology, 17(2), pp.605-614. In this publication the finite element model, material set assignment and local orientations are provided. This dataset contains an inp file in the syntax of Abaqus/Standard software v2017. 

Topologically interlocked stereotomic material (TISM) systems are load-carrying assemblies of unit elements interacting by contact and friction. Past research on these material systems has demonstrated attractive mechanical response characteristics, including damage tolerance, impact resistance, adaptive property control, tuneable acoustical characteristics, as well as disassembly and reuse. In this work, we aim to expand the range of topologically interlocked material systems for which such response is found. The theory of tessellations is the underpinning to create new material systems. We present a comparative study on the deflection response to transverse loading for two underlying tessellations and boundary conditions. Williams, A., & Siegmund, T. (2018). Tesselations and Percolations in Topologically Interlocked Stereotomic Material Systems. In T. Siegmund & F. Barthelat (Eds.) Proceedings of the IUTAM Symposium Architectured Materials Mechanics, September 17-19, 2018 , Chicago, IL: Purdue University Libraries Scholarly Publishing Services, 2018. https://docs.lib.purdue.edu/iutam/presentations/abstracts/79 

At the nanoscale bone is composed of aligned heterogeneously mineralized collagen fibrils. While raloxifene (Ral) and bisphosphonate (BP) treatment preserve bone mass, they also affect bone quality through changes in collagen hydration and mineral density/heterogeneity, respectively. It was hypothesized that the effects of pharmacological treatment on the tissue would alter linear microcracking in finite element (FE) models of trabeculae reflecting control (Ctrl), Ral and BP. A FE mesh of a single canine vertebral body trabecula was generated from a micro- CT scan using ScanIP. A custom MATLAB code imposed tissue property heterogeneity and a collagen fibril orientation parallel to the trabecular surface. Ctrl was heterogeneous (based on vBMD) in both modulus and strength, and BP was homogenous (+25% of Ctrl mean modulus and strength). Ctrl and BP models had identical microcracking toughness. Ral had increased microcracking toughness (+25%) and the same modulus and strength heterogeneity as Ctrl. Transverse deflections were applied to simulate bending of the trabeculae, microcrack formation and propagation was simulated with the imposed orientation using the extended FE method in Abaqus/Standard, and the energy dissipated by the microcrack was assessed. 

At the nanoscale bone is composed of aligned mineralized collagen fibrils organized into packets along the surface of trabecular bone creating an anisotropic tissue microstructure. Newer packets at the trabecular surfaces are usually less mineralized than older bone in the interior of the trabeculae, which along with irregular mineral deposition within packets, forms a heterogeneous material across the span of a trabeculae. However, finite element (FE) models of bone typically use homogenous isotropic material properties, because it is challenging to build anisotropy and heterogeneity into a model in a way that is applicable to the complex geometries of trabecular bone. Both the material anisotropy and heterogeneity may influence the stress state of trabecular bone, and it is important to understand the implications of such differences for determining bone biomechanical failure. It was hypothesized that taking into consideration both the tissue anisotropy and heterogeneity of bone’s biomechanical properties would alter the expected failure locations by reducing tensile stress on near surface elements of an FE model of canine trabecular bone. The objective of this study was to test this hypothesis and to develop a method to apply anisotropic and heterogeneous material properties to a model automatically from micro-computed tomography (μCT) data.