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Apparent Density

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José M. Guedes – One of the best experts on this subject based on the ideXlab platform.

  • numerical modeling of bone tissue adaptation a hierarchical approach for bone Apparent Density and trabecular structure
    Journal of Biomechanics, 2009
    Co-Authors: Pedro Coelho, Paulo R. Fernandes, Helder C. Rodrigues, João Mário Burguete Botelho Cardoso, José M. Guedes

    Abstract:

    In this work, a three-dimensional model for bone remodeling is presented, taking into account the hierarchical structure of bone. The process of bone tissue adaptation is mathematically described with respect to functional demands, both mechanical and biological, to obtain the bone Apparent Density distribution (at the macroscale) and the trabecular structure (at the microscale). At global scale bone is assumed as a continuum material characterized by equivalent (homogenized) mechanical properties. At local scale a periodic cellular material model approaches bone trabecular anisotropy as well as bone surface area Density. For each scale there is a material distribution problem governed by Density-based design variables which at the global level can be identified with bone relative Density. In order to show the potential of the model, a three-dimensional example of the proximal femur illustrates the distribution of bone Apparent Density as well as microstructural designs characterizing both anisotropy and bone surface area Density. The bone Apparent Density numerical results show a good agreement with Dual-energy X-ray Absorptiometry (DXA) exams. The material symmetry distributions obtained are comparable to real bone microstructures depending on the local stress field. Furthermore, the compact bone porosity is modeled giving a transversal isotropic behavior close to the experimental data. Since, some computed microstructures have no permeability one concludes that bone tissue arrangement is not a simple stiffness maximization issue but biological factors also play an important role.

  • Numerical modeling of bone tissue adaptation—A hierarchical approach for bone Apparent Density and trabecular structure
    Journal of Biomechanics, 2009
    Co-Authors: Pedro Coelho, Paulo R. Fernandes, Helder C. Rodrigues, João Mário Burguete Botelho Cardoso, José M. Guedes

    Abstract:

    In this work, a three-dimensional model for bone remodeling is presented, taking into account the hierarchical structure of bone. The process of bone tissue adaptation is mathematically described with respect to functional demands, both mechanical and biological, to obtain the bone Apparent Density distribution (at the macroscale) and the trabecular structure (at the microscale). At global scale bone is assumed as a continuum material characterized by equivalent (homogenized) mechanical properties. At local scale a periodic cellular material model approaches bone trabecular anisotropy as well as bone surface area Density. For each scale there is a material distribution problem governed by Density-based design variables which at the global level can be identified with bone relative Density. In order to show the potential of the model, a three-dimensional example of the proximal femur illustrates the distribution of bone Apparent Density as well as microstructural designs characterizing both anisotropy and bone surface area Density. The bone Apparent Density numerical results show a good agreement with Dual-energy X-ray Absorptiometry (DXA) exams. The material symmetry distributions obtained are comparable to real bone microstructures depending on the local stress field. Furthermore, the compact bone porosity is modeled giving a transversal isotropic behavior close to the experimental data. Since, some computed microstructures have no permeability one concludes that bone tissue arrangement is not a simple stiffness maximization issue but biological factors also play an important role.

Pedro Coelho – One of the best experts on this subject based on the ideXlab platform.

  • numerical modeling of bone tissue adaptation a hierarchical approach for bone Apparent Density and trabecular structure
    Journal of Biomechanics, 2009
    Co-Authors: Pedro Coelho, Paulo R. Fernandes, Helder C. Rodrigues, João Mário Burguete Botelho Cardoso, José M. Guedes

    Abstract:

    In this work, a three-dimensional model for bone remodeling is presented, taking into account the hierarchical structure of bone. The process of bone tissue adaptation is mathematically described with respect to functional demands, both mechanical and biological, to obtain the bone Apparent Density distribution (at the macroscale) and the trabecular structure (at the microscale). At global scale bone is assumed as a continuum material characterized by equivalent (homogenized) mechanical properties. At local scale a periodic cellular material model approaches bone trabecular anisotropy as well as bone surface area Density. For each scale there is a material distribution problem governed by Density-based design variables which at the global level can be identified with bone relative Density. In order to show the potential of the model, a three-dimensional example of the proximal femur illustrates the distribution of bone Apparent Density as well as microstructural designs characterizing both anisotropy and bone surface area Density. The bone Apparent Density numerical results show a good agreement with Dual-energy X-ray Absorptiometry (DXA) exams. The material symmetry distributions obtained are comparable to real bone microstructures depending on the local stress field. Furthermore, the compact bone porosity is modeled giving a transversal isotropic behavior close to the experimental data. Since, some computed microstructures have no permeability one concludes that bone tissue arrangement is not a simple stiffness maximization issue but biological factors also play an important role.

  • Numerical modeling of bone tissue adaptation—A hierarchical approach for bone Apparent Density and trabecular structure
    Journal of Biomechanics, 2009
    Co-Authors: Pedro Coelho, Paulo R. Fernandes, Helder C. Rodrigues, João Mário Burguete Botelho Cardoso, José M. Guedes

    Abstract:

    In this work, a three-dimensional model for bone remodeling is presented, taking into account the hierarchical structure of bone. The process of bone tissue adaptation is mathematically described with respect to functional demands, both mechanical and biological, to obtain the bone Apparent Density distribution (at the macroscale) and the trabecular structure (at the microscale). At global scale bone is assumed as a continuum material characterized by equivalent (homogenized) mechanical properties. At local scale a periodic cellular material model approaches bone trabecular anisotropy as well as bone surface area Density. For each scale there is a material distribution problem governed by Density-based design variables which at the global level can be identified with bone relative Density. In order to show the potential of the model, a three-dimensional example of the proximal femur illustrates the distribution of bone Apparent Density as well as microstructural designs characterizing both anisotropy and bone surface area Density. The bone Apparent Density numerical results show a good agreement with Dual-energy X-ray Absorptiometry (DXA) exams. The material symmetry distributions obtained are comparable to real bone microstructures depending on the local stress field. Furthermore, the compact bone porosity is modeled giving a transversal isotropic behavior close to the experimental data. Since, some computed microstructures have no permeability one concludes that bone tissue arrangement is not a simple stiffness maximization issue but biological factors also play an important role.

J Bollerslev – One of the best experts on this subject based on the ideXlab platform.

  • decreased trabecular bone biomechanical competence Apparent Density igf ii and igfbp 5 content in acromegaly
    European Journal of Clinical Investigation, 2002
    Co-Authors: Thor Ueland, Kim Brixen, E N Ebbesen, Jesper Skovhus Thomsen, L Mosekilde, Allan Flyvbjerg, J Bollerslev

    Abstract:

    Background Earlier studies on the effect of excess growth hormone (GH) on trabecular bone have been conflicting. Since insulin-like growth factors (IGFs) and their binding proteins (IGFBPs) in part mediate the effects of GH, the present study aimed to investigate trabecular bone composition of these growth factors in relation to biomechanical properties in acromegaly.

    Materials and methods Trabecular bone biomechanical competence (compression test), Apparent Density (peripheral quantitative computed tomography, pQCT), and bone matrix contents of calcium (HCl hydrolysis) and IGFs (guanidinium–HCl extraction) were measured in iliac crest biopsies from 13 patients with active acromegaly (two women and 11 men, aged 21–61 years) and 21 age- and sex-matched controls (four women and 17 men, aged 23–64 years).

    Results Trabecular bone pQCT was reduced in acromegalic patients compared with controls (P = 0·005), as was biomechanical competence (P < 0·05 for all measures). These parameters were significantly positively correlated in both acromegalic patients and controls. The calcium content of trabecular bone was significantly increased in patients compared with controls. No significant differences were found in trabecular bone content of IGF-I, IGFBP-3, or osteocalcin. However, IGF-II and IGFBP-5 content was decreased (P < 0·001 and P < 0·05, respectively). Conclusions The present study demonstrates reduced trabecular biomechanical competence and Apparent Density in acromegaly, supporting previous observations of an unfavourable effect of chronic excess GH on the axial skeleton. Furthermore, we demonstrate decreased trabecular bone content of IGF-II and IGFBP-5 in these patients. However, we found no direct causal relationship between trabecular bone Density and bone content of IGF-system components.