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1
Cowin, S. C. "Torsion of Cylinders With Shape Intrinsic Orthotropy." Journal of Applied Mechanics 54, no. 4 (December 1, 1987): 778–82. http://dx.doi.org/10.1115/1.3173116.
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Shape intrinsic orthotropy may be thought of as the type of elastic material symmetry possessed by the wood tissue of a tree. Each year’s new growth rings form a laminate around a central core. The axes of material symmetry lie in the directions tangent and normal to the growth rings or laminates and along the axis of the cylinder. Let Gtz denote the linear elastic orthotropic shear modulus associated with the axial and tangential directions, the tangent plane of a laminate. It is shown here that, for a certain class of elastic cylinders with shape intrinsic orthotropy, the solution to the torsion problem is the same as the solution to the torsion problem for the isotropic cylinder of the same shape if the isotropic shear modulus G were replaced by the orthotropic shear modulus Gtz.
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Kawamura, Koji, and Hiroshi Takeda. "Rules of crown development in the clonal shrub Vaccinium hirtum in a low-light understory: a quantitative analysis of architecture." Canadian Journal of Botany 82, no. 3 (March 1, 2004): 329–39. http://dx.doi.org/10.1139/b04-001.
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The rules of crown development in the clonal shrub Vaccinium hirtum Thunb. in a low-light understory were identified by architectural analysis, and the structure and dynamics of current-year shoots were quantified. Development started from an initial orthotropic axis, which forked into plagiotropic axes; consequently, arched stems were formed. Subsequently, a new orthotropic shoot arose from the dormant meristem on the stem. The process from orthotrophy to plagiotrophy was then repeated. Ramets developed vertically as a result of the repeated formation of such orthotropic shoots and reached a maximum height of about 2 m. These processes were mainly characterized by the sequential change from orthotrophy to plagiotrophy in stem orientation and by a sequential reduction in shoot growth, in which a long shoot forked into shorter shoots with increasing allocation to leaves relative to stems. These rules may be adaptive for efficient light capture under conditions of low light availability, in terms of a low degree of self-shading and low cost of supporting tissue. Simultaneously, these rules worked to restrict the developmental potential of crowns, including the lateral expansion of crowns and the longevity of branch systems. This may be associated with a shrub-specific, throwaway design for stems that are expendable in high-stress environments.Key words: crown architecture, branching, leaf display, architectural unit, reiteration.
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Zysset, P. K., R. W. Goulet, and S. J. Hollister. "A Global Relationship Between Trabecular Bone Morphology and Homogenized Elastic Properties." Journal of Biomechanical Engineering 120, no. 5 (October 1, 1998): 640–46. http://dx.doi.org/10.1115/1.2834756.
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An alternative concept of the relationship between morphological and elastic properties of trabecular bone is presented and applied to human tissue from several anatomical locations using a digital approach. The three-dimensional morphology of trabecular bone was assessed with a microcomputed tomography system and the method of directed secants as well as the star volume procedure were used to compute mean intercept length (MIL) and average bone length (ABL) of 4 mm cubic specimens. Assuming isotropic elastic properties for the trabecular tissue, the general elastic tensors of the bone specimens were determined using the homogenization method and the closest orthotropic tensors were calculated with an optimization algorithm. The assumption of orthotropy for trabecular bone was found to improve with specimen size and hold within 6.1 percent for a 4 mm cube size. A strong global relationship (r2 = 0.95) was obtained between fabric and the orthotropic elastic tensor with a minimal set of five constants. Mean intercept length and average bone length provided an equivalent power of prediction. These results support the hypothesis that the elastic properties of human trabecular bone from an arbitrary anatomical location can be estimated from an approximation of the anisotropic morphology and a prior knowledge of tissue properties.
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Benson, Alan P., Olivier Bernus, Hans Dierckx, Stephen H. Gilbert, John P. Greenwood, Arun V. Holden, Kevin Mohee, et al. "Construction and validation of anisotropic and orthotropic ventricular geometries for quantitative predictive cardiac electrophysiology." Interface Focus 1, no. 1 (December 3, 2010): 101–16. http://dx.doi.org/10.1098/rsfs.2010.0005.
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Reaction–diffusion computational models of cardiac electrophysiology require both dynamic excitation models that reconstruct the action potentials of myocytes as well as datasets of cardiac geometry and architecture that provide the electrical diffusion tensor D , which determines how excitation spreads through the tissue. We illustrate an experimental pipeline we have developed in our laboratories for constructing and validating such datasets. The tensor D changes with location in the myocardium, and is determined by tissue architecture. Diffusion tensor magnetic resonance imaging (DT-MRI) provides three eigenvectors e i and eigenvalues λ i at each voxel throughout the tissue that can be used to reconstruct this architecture. The primary eigenvector e 1 is a histologically validated measure of myocyte orientation (responsible for anisotropic propagation). The secondary and tertiary eigenvectors ( e 2 and e 3 ) specify the directions of any orthotropic structure if λ 2 is significantly greater than λ 3 —this orthotropy has been identified with sheets or cleavage planes. For simulations, the components of D are scaled in the fibre and cross-fibre directions for anisotropic simulations (or fibre, sheet and sheet normal directions for orthotropic tissues) so that simulated conduction velocities match values from optical imaging or plunge electrode experiments. The simulated pattern of propagation of action potentials in the models is partially validated by optical recordings of spatio-temporal activity on the surfaces of hearts. We also describe several techniques that enhance components of the pipeline, or that allow the pipeline to be applied to different areas of research: Q ball imaging provides evidence for multi-modal orientation distributions within a fraction of voxels, infarcts can be identified by changes in the anisotropic structure—irregularity in myocyte orientation and a decrease in fractional anisotropy, clinical imaging provides human ventricular geometry and can identify ischaemic and infarcted regions, and simulations in human geometries examine the roles of anisotropic and orthotropic architecture in the initiation of arrhythmias.
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Holzapfel, Gerhard A., and Ray W. Ogden. "Constitutive modelling of passive myocardium: a structurally based framework for material characterization." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 367, no. 1902 (September 13, 2009): 3445–75. http://dx.doi.org/10.1098/rsta.2009.0091.
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In this paper, we first of all review the morphology and structure of the myocardium and discuss the main features of the mechanical response of passive myocardium tissue, which is an orthotropic material. Locally within the architecture of the myocardium three mutually orthogonal directions can be identified, forming planes with distinct material responses. We treat the left ventricular myocardium as a non-homogeneous, thick-walled, nonlinearly elastic and incompressible material and develop a general theoretical framework based on invariants associated with the three directions. Within this framework we review existing constitutive models and then develop a structurally based model that accounts for the muscle fibre direction and the myocyte sheet structure. The model is applied to simple shear and biaxial deformations and a specific form fitted to the existing (and somewhat limited) experimental data, emphasizing the orthotropy and the limitations of biaxial tests. The need for additional data is highlighted. A brief discussion of issues of convexity of the model and related matters concludes the paper.
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Semenova, Elena, Nikita Kharin, Pavel Bolshakov, Anastasiya Ivanova, and Viktoriya Yaikova. "Automatic processing and analysis of the structural properties of bone tissue." MATEC Web of Conferences 329 (2020): 03077. http://dx.doi.org/10.1051/matecconf/202032903077.
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The volumetric distribution of bone tissue can be analysed in terms of orthotropic medium. In this case, it is important to define the orthotropic directions. Nowadays, computed tomography methods allow getting such information. The method for automation such analysis is presented. Firstly, the threshold of binarization should be calculated. Then the sample should be meshed and each element should be binarized. After that fabric tensor, eigenvalues, eigenvectors and fractional anisotropy can be calculated for each element. Statistical methods were used to analyse the field of the obtained data. Described methods were used on a bone sample. It was shown that for a sample the fabric tensor is constant and the fractional anisotropy is close to zero. That’s means that the medium in the sample was isotropic.
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Turner, C. H., and S. C. Cowin. "Errors Induced by Off-Axis Measurement of the Elastic Properties of Bone." Journal of Biomechanical Engineering 110, no. 3 (August 1, 1988): 213–15. http://dx.doi.org/10.1115/1.3108433.
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Misalignment between the axes of measurement and the material symmetry axes of bone causes error in anisotropic elastic property measurements. Measurements of Poisson’s ratio were strongly affected by misalignment errors. The mean errors in the measured Young’s moduli were 9.5 and 1.3 percent for cancellous and cortical bone, respectively, at a misalignment angle of 10 degrees. Mean errors of 1.1 and 5.0 percent in the measured shear moduli for cancellous and cortical bone, respectively, were found at a misalignment angle of 10 degrees. Although, cancellous bone tissue was assumed to have orthotropic elastic symmetry, the possibility of the greater symmetry of transverse isotropy was investigated. When the nine orthotropic elastic constants were forced to approximate the five transverse isotropic elastic constants, errors of over 60 percent were introduced. Therefore, it was concluded that cancellous bone is truly orthotropic and not transversely isotropic. A similar but less strong result for cortical bone tissue was obtained.
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Ruiz-Baier, Ricardo. "Modelling Thermo-Electro-Mechanical Effects in Orthotropic Cardiac Tissue." Communications in Computational Physics 27, no. 1 (June 2020): 87–115. http://dx.doi.org/10.4208/cicp.oa-2018-0253.
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Koombua, Kittisak, and Ramana M. Pidaparti. "Inhalation Induced Stresses and Flow Characteristics in Human Airways through Fluid-Structure Interaction Analysis." Modelling and Simulation in Engineering 2008 (2008): 1–8. http://dx.doi.org/10.1155/2008/358748.
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Better understanding of stresses and flow characteristics in the human airways is very important for many clinical applications such as aerosol drug therapy, inhalation toxicology, and airway remodeling process. The bifurcation geometry of airway generations 3 to 5 based on the ICRP tracheobronchial model was chosen to analyze the flow characteristics and stresses during inhalation. A computational model was developed to investigate the airway tissue flexibility effect on stresses and flow characteristics in the airways. The finite-element method with the fluid-structure interaction analysis was employed to investigate the transient responses of the flow characteristics and stresses in the airways during inhalation. The simulation results showed that tissue flexibility affected the maximum airflow velocity, airway pressure, and wall shear stress about 2%, 7%, and 6%, respectively. The simulation results also showed that the differences between the orthotropic and isotropic material models on the airway stresses were in the ranges of 25–52%. The results from the present study suggest that it is very important to incorporate the orthotropic tissue properties into a computational model for studying flow characteristics and stresses in the airways.
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Pervolaraki, Eleftheria, Richard A. Anderson, Alan P. Benson, Barrie Hayes-Gill, Arun V. Holden, Benjamin J. R. Moore, Martyn N. Paley, and Henggui Zhang. "Antenatal architecture and activity of the human heart." Interface Focus 3, no. 2 (April 6, 2013): 20120065. http://dx.doi.org/10.1098/rsfs.2012.0065.
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We construct the components for a family of computational models of the electrophysiology of the human foetal heart from 60 days gestational age (DGA) to full term. This requires both cell excitation models that reconstruct the myocyte action potentials, and datasets of cardiac geometry and architecture. Fast low-angle shot and diffusion tensor magnetic resonance imaging (DT-MRI) of foetal hearts provides cardiac geometry with voxel resolution of approximately 100 μm. DT-MRI measures the relative diffusion of protons and provides a measure of the average intravoxel myocyte orientation, and the orientation of any higher order orthotropic organization of the tissue. Such orthotropic organization in the adult mammalian heart has been identified with myocardial sheets and cleavage planes between them. During gestation, the architecture of the human ventricular wall changes from being irregular and isotropic at 100 DGA to an anisotropic and orthotropic architecture by 140 DGA, when it has the smooth, approximately 120° transmural change in myocyte orientation that is characteristic of the adult mammalian ventricle. The DT obtained from DT-MRI provides the conductivity tensor that determines the spread of potential within computational models of cardiac tissue electrophysiology. The foetal electrocardiogram (fECG) can be recorded from approximately 60 DGA, and RR, PR and QT intervals between the P, R, Q and T waves of the fECG can be extracted by averaging from approximately 90 DGA. The RR intervals provide a measure of the pacemaker rate, the QT intervals an index of ventricular action potential duration, and its rate-dependence, and so these intervals constrain and inform models of cell electrophysiology. The parameters of models of adult human sinostrial node and ventricular cells that are based on adult cell electrophysiology and tissue molecular mapping have been modified to construct preliminary models of foetal cell electrophysiology, which reproduce these intervals from fECG recordings. The PR and QR intervals provide an index of conduction times, and hence propagation velocities (approx. 1–10 cm s −1 , increasing during gestation) and so inform models of tissue electrophysiology. Although the developing foetal heart is small and the cells are weakly coupled, it can support potentially lethal re-entrant arrhythmia.
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Waffenschmidt, Tobias, and Andreas Menzel. "On a micro-sphere based remodelling formulation for orthotropic soft biological tissue." PAMM 10, no. 1 (December 2010): 747–48. http://dx.doi.org/10.1002/pamm.201010353.
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Pugno, Nicola Maria, and Qiang Chen. "Modeling the Elastic Anisotropy of Woven Hierarchical Tissues: Experimental Comparison on Biological Materials and Design of a New Class of Scaffolds." Advances in Science and Technology 76 (October 2010): 153–58. http://dx.doi.org/10.4028/www.scientific.net/ast.76.153.
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This paper models the elastic properties of 2-D woven hierarchical tissues, assuming an orthotropic material of warp and fill yarns at level 0. Considering matrix transformation and stiffness averaging, stiffness matrices of warp and fill yarns of the tissue at level i are employed to calculate those of the tissue at level i+1. We compare our theory with another approach from the literature on tendons and experiments on leaves performed by ourselves. The result shows the possibility of designing a new class of hierarchical 2-D scaffolds with desired elastic anisotropy, better matching the anisotropy of the biological tissues and thus maximizing the regeneration.
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Cansiz, Baris, Hüsnü Dal, and Michael Kaliske. "Computational modeling of cardiac tissue with strongly coupled electromechanics and orthotropic viscoelastic effects." PAMM 14, no. 1 (December 2014): 119–20. http://dx.doi.org/10.1002/pamm.201410047.
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Vorp, David Alan. "Finite element modelling and analyses of nonlinearly elastic, orthotropic, vascular tissue in distension." Annals of Biomedical Engineering 21, no. 6 (November 1993): 736–37. http://dx.doi.org/10.1007/bf02368653.
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Colli Franzone, Piero, Luca F. Pavarino, and Simone Scacchi. "Bioelectrical effects of mechanical feedbacks in a strongly coupled cardiac electro-mechanical model." Mathematical Models and Methods in Applied Sciences 26, no. 01 (November 2, 2015): 27–57. http://dx.doi.org/10.1142/s0218202516500020.
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The aim of this work is to investigate by means of numerical simulations the effects of myocardial deformation due to muscle contraction on the bioelectrical activity of the cardiac tissue. The three-dimensional electro-mechanical model considered consists of the following four components: the quasi-static orthotropic finite elasticity equations for the deformation of the cardiac tissue; the active tension model for the intracellular calcium dynamics and cross-bridge binding; the orthotropic Bidomain model for the electrical current flow through the tissue; the membrane model of the cardiac myocyte, including stretch-activated currents (I SAC ). In order to properly take into account cardiac mechanical feedbacks, the electrical current flow is described in a strongly coupled framework by the Bidomain model on the deformed tissue. We then derive a novel formulation of the Bidomain model in the reference configuration, with complete mechanical feedbacks affecting not only the conductivity tensors but also a convective term depending on the velocity of the deformation. The numerical simulations are based on our finite element parallel solver, which employs both Multilevel Additive Schwarz preconditioners for the solution of linear systems arising from the discretization of the Bidomain equations and Newton–Krylov-Algebraic Multigrid methods for the solution of nonlinear systems arising from the discretization of the finite elasticity equations. The results have shown that: (i) the I SAC current prolongs action potential duration (APD) of about 10–15 ms; (ii) the inclusion into the model of both I SAC current and the convective term reduces the dispersion of repolarization of about 7% (from 139 to 129 ms) and increases the dispersion of APD about three times (from 13 to 45 ms). These effects indicate that mechanical feedbacks might influence arrhythmogenic mechanisms when combined with pathological substrates.
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Yablonsky, P. P., and S. M. Yashin. "The first experience of orthotropic implantation of decellularized mitral allograft." Scientific Notes of the I. P. Pavlov St. Petersburg State Medical University 22, no. 3 (September 30, 2015): 64–65. http://dx.doi.org/10.24884/1607-4181-2015-22-3-64-65.
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Traditional biological and mechanical valve substitutes have some well-known limitation, such as rapid deterioration of the tissue ones in young patient and the high risk of thrombosis and anticoagulation therapy complications for the mechanical ones. At the same time the aortic and pulmonary valves can already be replaced with decellularized allografts that showed promising results in terms of both hemodynamics and reliability while anticoagulation for them is not needed. This paper describes the first orthotropic implantation of the decellularized mitral valve allograft in sheep model. The original method without stabilizing ring is described, which have shown good echocardiographic results.
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MARTIN, M., T. LEMAIRE, G. HAIAT, P. PIVONKA, and V. SANSALONE. "BONE ORTHOTROPIC REMODELING AS A THERMODYNAMICALLY-DRIVEN EVOLUTION." Journal of Mechanics in Medicine and Biology 20, no. 04 (May 2020): 1950084. http://dx.doi.org/10.1142/s0219519419500842.
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In this paper, we present and discuss a model of bone remodeling set up in the framework of the theory of generalized continuum mechanics which was first introduced by DiCarlo et al. [Sur le remodelage des tissus osseux anisotropes, Comptes Rendus Mécanique 334(11):651–661, 2006]. Bone is described as an orthotropic body experiencing remodeling as a rotation of its microstructure. Thus, the complete kinematic description of a material point is provided by its position in space and a rotation tensor describing the orientation of its microstructure. Material motion is driven by energetic considerations, namely by the application of the Clausius–Duhem inequality to the microstructured material. Within this framework of orthotropic remodeling, some key features of the remodeling equilibrium configurations are deduced in the case of homogeneous strain or stress loading conditions. First, it is shown that remodeling equilibrium configurations correspond to energy extrema. Second, stability of the remodeling equilibrium configurations is assessed in terms of the local convexity of the strain and complementary energy functionals hence recovering some classical energy theorems. Eventually, it is shown that the remodeling equilibrium configurations are not only highly dependent on the loading conditions, but also on the material properties.
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Basaruddin, Khairul Salleh, and Naoki Takano. "Estimation of Apparent Elastic Moduli of Trabecular Bone Considering Biological Apatite (BAp) Crystallite Orientation in Tissue Modulus." Advanced Materials Research 894 (February 2014): 167–71. http://dx.doi.org/10.4028/www.scientific.net/amr.894.167.
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This study presents a prediction of apparent elastic moduli of vertebral trabecular bone using the homogenization method. A micro-finite element (FE) model of trabecular bone was reconstructed from a sequential of cross-section micro-CT image by converting bone voxels to brick elements. Eight regions of interest (ROIs) were extracted from two lumbar vertebra bone specimens of healthy and osteoporotic. The homogenization method and finite element method was employed to analyze the microscopic trabecular bone. Bone tissue property was modeled as orthotropy material considering the biological apatite (BAp) crystallite orientation. This research focuses on the effect of morphological difference between healthy and osteoporotic bones to the apparent elastic moduli. The change of degree of anisotropy was also discussed. Comparison of the calculated Youngs moduli in vertical axis with Keyak et al.s experimental result showed good agreement and proved the reliability of the numerical model.
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Barrera, John W., Adeline Le Cabec, and Meir M. Barak. "The orthotropic elastic properties of fibrolamellar bone tissue in juvenile white-tailed deer femora." Journal of Anatomy 229, no. 4 (May 27, 2016): 568–76. http://dx.doi.org/10.1111/joa.12500.
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Flynn, D. M., G. D. Peura, P. Grigg, and A. H. Hoffman. "A Finite Element Based Method to Determine the Properties of Planar Soft Tissue." Journal of Biomechanical Engineering 120, no. 2 (April 1, 1998): 202–10. http://dx.doi.org/10.1115/1.2798303.
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A finite element based method to determine the incremental elastic material properties of planar membranes was developed and evaluated. The method is applicable to tissues that exhibit inhomogeneity, geometric and material nonlinearity, and anisotropy. Markers are placed on the tissue to form a four-node quadrilateral element. The specimen is loaded to an initial reference state, then three incremental loading sets are applied and the nodal displacements recorded. One of these loadings must include shear. These data are used to solve an over-determined system of equations for the tangent stiffness matrix. The method was first verified using analytical data. Next, data obtained from a latex rubber sheet were used to evaluate experimental procedures. Finally, experiments conducted on preconditioned rat skin revealed non-linear orthotropic behavior. The vector norm comparing the applied and calculated nodal force vectors was used to evaluate the accuracy of the solutions.
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Schmid, H., M. P. Nash, A. A. Young, O. Röhrle, and P. J. Hunter. "A Computationally Efficient Optimization Kernel for Material Parameter Estimation Procedures." Journal of Biomechanical Engineering 129, no. 2 (September 21, 2006): 279–83. http://dx.doi.org/10.1115/1.2540860.
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Estimating material parameters is an important part in the study of soft tissue mechanics. Computational time can easily run to days, especially when all available experimental data are taken into account. The material parameter estimation procedure is examplified on a set of homogeneous simple shear experiments to estimate the orthotropic constitutive parameters of myocardium. The modification consists of changing the traditional least-squares approach to a weighted least-squares. This objective function resembles a L2-norm type integral which is approximated using Gaussian quadrature. This reduces the computational time of the material parameter estimation by two orders of magnitude.
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Kohles, Sean S., and Julie B. Roberts. "Linear Poroelastic Cancellous Bone Anisotropy: Trabecular Solid Elastic and Fluid Transport Properties." Journal of Biomechanical Engineering 124, no. 5 (September 30, 2002): 521–26. http://dx.doi.org/10.1115/1.1503374.
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The mechanical performance of cancellous bone is characterized using experiments which apply linear poroelasticity theory. It is hypothesized that the anisotropic organization of the solid and pore volumes of cancellous bone can be physically characterized separately (no deformable boundary interactive effects) within the same bone sample. Due to its spongy construction, the in vivo mechanical function of cancellous or trabecular bone is dependent upon fluid and solid materials which may interact in a hydraulic, convective fashion during functional loading. This project provides insight into the organization of the tissue, i.e., the trabecular connectivity, by defining the separate nature of this biphasic performance. Previous fluid flow experiments [Kohles et al., 2001, Journal of Biomechanics, 34(11), pp. 1197–1202] describe the pore space via orthotropic permeability. Ultrasonic wave propagation through the trabecular network is used to describe the solid component via orthotropic elastic moduli and material stiffness coefficients. The linear poroelastic nature of the tissue is further described by relating transport (fluid flow) and elasticity (trabecular load transmission) during regression analysis. In addition, an empirical relationship between permeability and porosity is applied to the collected data. Mean parameters in the superior-inferior (SI) orientation of cubic samples n=20 harvested from a single bovine distal femur were the largest p<0.05 in comparison to medial-lateral (ML) and anterior-posterior (AP) orientations: Apparent elastic modulus (2,139 MPa), permeability (4.65×10−10 m2), and material stiffness coefficient (13.6 GPa). A negative correlation between permeability as a predictor of structural elastic modulus supported a parametric relationship in the ML R2=0.4793, AP R2=0.3018, and SI R2=0.6445 directions p<0.05.
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Taber, L. A. "On a Nonlinear Theory for Muscle Shells: Part I—Theoretical Development." Journal of Biomechanical Engineering 113, no. 1 (February 1, 1991): 56–62. http://dx.doi.org/10.1115/1.2894085.
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This paper presents a theory for studies of the large-strain behavior of biological shells composed of layers of incompressible, orthotropic tissue, possibly muscle, of arbitrary orientation. The intrinsic equations of the laminated-shell theory, expressed in lines-of-curvature coordinates, account for large membrane [O(1)] and moderately large bending and transverse shear strains [O(0.3)], nonlinear material properties, and transverse normal stress and strain. An expansion is derived for a general two-dimensional strain-energy density function, which includes residual stress and muscle activation through a shifting zero-stress configuration. Strain-displacement relations are given for the special case of axisymmetric deformation of shells of revolution with torsion.
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Horbach, Andreas J., and Manfred Staat. "Optical strain measurement for the modeling of surgical meshes and their porosity." Current Directions in Biomedical Engineering 4, no. 1 (September 1, 2018): 181–84. http://dx.doi.org/10.1515/cdbme-2018-0045.
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AbstractThe porosity of surgical meshes makes them flexible for large elastic deformation and establishes the healing conditions of good tissue in growth. The biomechanic modeling of orthotropic and compressible materials requires new materials models and simulstaneoaus fit of deformation in the load direction as well as trannsversely to to load. This nonlinear modeling can be achieved by an optical deformation measurement. At the same time the full field deformation measurement allows the dermination of the change of porosity with deformation. Also the socalled effective porosity, which has been defined to asses the tisssue interatcion with the mesh implants, can be determined from the global deformation of the surgical meshes.
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Ma, Yibo, Feng Qian, Jianfeng Wang, Yanping Liu, and Shuiqing Liu. "Primary accessory thyroid carcinoma with negative 99mTcO4− SPECT/CTimaging: a case report and literature review." Journal of International Medical Research 47, no. 8 (July 15, 2019): 3934–39. http://dx.doi.org/10.1177/0300060519859738.
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Introduction In contrast to orthotopic thyroid carcinoma, primary accessory thyroid carcinoma is very rare. We herein report a case involving primary accessory thyroid carcinoma in a patient with normal ultrasonography of the orthotopic thyroid and negative 99mTcO4− single-photon emission computed tomography (SPECT) scintigraphy. Case presentation: A computed tomography (CT) scan showed soft tissue nodules at the left anterior edge of the thyroid cartilage. To determine whether the mass was accessory thyroid tissue, 99mTcO4− SPECT/CT was performed, and the findings were negative. However, pathological examination after resection showed that mass was a primary accessory thyroid papillary carcinoma. The 1-year follow-up ultrasound showed no lesion at the orthotropic thyroid and neck incision sites. Conclusions This case suggests that negative 99mTcO4− SPECT/CT imaging may not completely exclude the possibility of thyroid carcinoma. A punch biopsy or postoperative pathological examination is necessary for the diagnosis.
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Propp, Adrienne, Alessio Gizzi, Francesc Levrero-Florencio, and Ricardo Ruiz-Baier. "An orthotropic electro-viscoelastic model for the heart with stress-assisted diffusion." Biomechanics and Modeling in Mechanobiology 19, no. 2 (October 19, 2019): 633–59. http://dx.doi.org/10.1007/s10237-019-01237-y.
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Abstract We propose and analyse the properties of a new class of models for the electromechanics of cardiac tissue. The set of governing equations consists of nonlinear elasticity using a viscoelastic and orthotropic exponential constitutive law, for both active stress and active strain formulations of active mechanics, coupled with a four-variable phenomenological model for human cardiac cell electrophysiology, which produces an accurate description of the action potential. The conductivities in the model of electric propagation are modified according to stress, inducing an additional degree of nonlinearity and anisotropy in the coupling mechanisms, and the activation model assumes a simplified stretch–calcium interaction generating active tension or active strain. The influence of the new terms in the electromechanical model is evaluated through a sensitivity analysis, and we provide numerical validation through a set of computational tests using a novel mixed-primal finite element scheme.
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Al Battah, Feras, Joery De Kock, Tamara Vanhaecke, and Vera Rogiers. "Current Status of Human Adipose–Derived Stem Cells: Differentiation into Hepatocyte-Like Cells." Scientific World JOURNAL 11 (2011): 1568–81. http://dx.doi.org/10.1100/tsw.2011.146.
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The shortage of human organ donors and the low cell quality of available liver tissues represent major obstacles for the clinical application of orthotropic liver transplantation and hepatocyte transplantation, respectively. Therefore, worldwide research groups are investigating alternative extrahepatic cell sources. Recentin vitrostudies have demonstrated that mesenchymal stem cells (MSCs) from various sources, including human bone marrow, adipose tissue, and umbilical cord, can be differentiated into hepatocyte-like cells when appropriate conditions are used. In particular, interest exists for human adipose–derived stems cells (hASCs) as an attractive cell source for generating hepatocyte-like cells. The hASCs are multipotent MSCs that reside in adipose tissue, with the ability to self-renew and differentiate into multiple cell lineages. Moreover, these cells can secrete multiple growth factors and cytokines that exert beneficial effects on organ or tissue injury. In this review, we will not only present recent data regarding hASC biology, their isolation, and differentiation capability towards hepatocytes, but also the potential application of hASC-derived hepatocytes to study drug toxicity. Additionally, this review will discuss the therapeutic potential of hASCs as undifferentiated cells in liver regeneration.
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CHEN, M. J., L. S. KIMPTON, J. P. WHITELEY, M. CASTILHO, J. MALDA, C. P. PLEASE, S. L. WATERS, and H. M. BYRNE. "Multiscale modelling and homogenisation of fibre-reinforced hydrogels for tissue engineering." European Journal of Applied Mathematics 31, no. 1 (November 22, 2018): 143–71. http://dx.doi.org/10.1017/s0956792518000657.
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Tissue engineering aims to grow artificial tissues in vitro to replace those in the body that have been damaged through age, trauma or disease. A recent approach to engineer artificial cartilage involves seeding cells within a scaffold consisting of an interconnected 3D-printed lattice of polymer fibres combined with a cast or printed hydrogel, and subjecting the construct (cell-seeded scaffold) to an applied load in a bioreactor. A key question is to understand how the applied load is distributed throughout the construct. To address this, we employ homogenisation theory to derive equations governing the effective macroscale material properties of a periodic, elastic–poroelastic composite. We treat the fibres as a linear elastic material and the hydrogel as a poroelastic material, and exploit the disparate length scales (small inter-fibre spacing compared with construct dimensions) to derive macroscale equations governing the response of the composite to an applied load. This homogenised description reflects the orthotropic nature of the composite. To validate the model, solutions from finite element simulations of the macroscale, homogenised equations are compared to experimental data describing the unconfined compression of the fibre-reinforced hydrogels. The model is used to derive the bulk mechanical properties of a cylindrical construct of the composite material for a range of fibre spacings and to determine the local mechanical environment experienced by cells embedded within the construct.
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Nam, Tran Huu. "Identification parameters of material model and large deformation analysis of inflated air-spring shell made of rubber-textile cord composite." Vietnam Journal of Mechanics 27, no. 2 (July 1, 2005): 118–28. http://dx.doi.org/10.15625/0866-7136/27/2/5721.
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In the paper an orthotropic hyperelastic constitutive model is presented which can be applied to numerical simulation for the response of biological soft tissue and of the nonlinear anisotropic hyperelastic material of the cylindrical air-spring shell used in vibroisolation of driver's seat. The parameters of strain energy function of the proposed constitutive model are fitted to the experimental results by the nonlinear least squares method. The deformation of the inflated cylindrical air-spring shell is calculated by solving the system of five first-order ordinary differential equations with the material constitutive law and proper boundary conditions. Numerical results of principal stretches and deformed profiles of the inflated cylindrical air-spring shell obtained by numerical deformation analysis are compared with experimental ones.
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Yahia, L. H., G. Drouin, and P. Duval. "A Methodology for Mechanical Measurements of Technical Constants of Trabecular Bone." Engineering in Medicine 17, no. 4 (October 1988): 169–73. http://dx.doi.org/10.1243/emed_jour_1988_017_044_02.
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Vertebral trabecular bone was tested by non-destructive uniaxial and triaxial loadings with the purpose of investigating the orthotropic properties of bone. A triaxial testing apparatus using hydrostatic pressure was developed and allowed to characterise the bony tissue in a three-dimensional stressed state. Thirty specimens, in the form of 10 mm cubes, were tested. The Young's moduli obtained in this study for the trabecular bone of human lumbar vertebrae are found to be in agreement with the values obtained by ultrasonic methods. Analyses of triaxial compressive tests provided, for the first time, the Poisson's ratios of vertebral trabecular bone. These values are found to satisfy thermodynamic restrictions established by Cowin and Van Buskirk (1986). Finally, no significant differences in the material properties were found for segment level (L3-L4).
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Atkinson, T. S., R. C. Haut, and N. J. Altiero. "A Poroelastic Model That Predicts Some Phenomenological Responses of Ligaments and Tendons." Journal of Biomechanical Engineering 119, no. 4 (November 1, 1997): 400–405. http://dx.doi.org/10.1115/1.2798285.
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Experimental evidence suggests that the tensile behavior of tendons and ligaments is in part a function of tissue hydration. The models currently available do not offer a means by which the hydration effects might be explicitly explored. To study these effects, a finite element model of a collagen sub-fascicle, a substructure of tendon and ligament, was formulated. The model was microstructurally based, and simulated oriented collagen fibrils with elastic-orthotropic continuum elements. Poroelastic elements were used to model the interfibrillar matrix. The collagen fiber morphology reflected in the model interacted with the interfibrillar matrix to produce behaviors similar to those seen in tendon and ligament during tensile, cyclic, and relaxation experiments conducted by others. Various states of hydration and permeability were parametrically investigated, demonstrating their influence on the tensile response of the model.
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Kwon, Jaeyoung, Junhyeok Ock, and Namkug Kim. "Mimicking the Mechanical Properties of Aortic Tissue with Pattern-Embedded 3D Printing for a Realistic Phantom." Materials 13, no. 21 (November 9, 2020): 5042. http://dx.doi.org/10.3390/ma13215042.
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3D printing technology has been extensively applied in the medical field, but the ability to replicate tissues that experience significant loads and undergo substantial deformation, such as the aorta, remains elusive. Therefore, this study proposed a method to imitate the mechanical characteristics of the aortic wall by 3D printing embedded patterns and combining two materials with different physical properties. First, we determined the mechanical properties of the selected base materials (Agilus and Dragonskin 30) and pattern materials (VeroCyan and TPU 95A) and performed tensile testing. Three patterns were designed and embedded in printed Agilus–VeroCyan and Dragonskin 30–TPU 95A specimens. Tensile tests were then performed on the printed specimens, and the stress-strain curves were evaluated. The samples with one of the two tested orthotropic patterns exceeded the tensile strength and strain properties of a human aorta. Specifically, a tensile strength of 2.15 ± 0.15 MPa and strain at breaking of 3.18 ± 0.05 mm/mm were measured in the study; the human aorta is considered to have tensile strength and strain at breaking of 2.0–3.0 MPa and 2.0–2.3 mm/mm, respectively. These findings indicate the potential for developing more representative aortic phantoms based on the approach in this study.
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Couet, Frédéric, Navneeta Rajan, Simone Vesentini, and D. Mantovani. "Design of a Collagen/Silk Mechano-Compatible Composite Scaffold for the Vascular Tissue Engineering: Focus on Compliance." Key Engineering Materials 334-335 (March 2007): 1169–72. http://dx.doi.org/10.4028/www.scientific.net/kem.334-335.1169.
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One of the merging methods to produce tissue-engineered vascular substitutes is to process scaffolds to direct the regeneration of vascular tissues. Collagen, as one of the main protein in the vascular extracellular matrix, is one of biopolymers that exhibits a major potential for scaffold technology. However, gels made from reconstituted collagen generally exhibit poor mechanical properties and limited manipulability. Therefore, adding a reinforcement to the scaffold to make the structure resist to the physiological constraints applied during the regeneration represents a valid alternative. Silk fibroin is an interesting reinforcing candidate being a mechanically strong natural fibre, susceptible to proteolytic degradation in vivo and showing acceptable biological performances. Therefore, the aim of this study was to develop a model of a composite scaffold obtained by controlling the filament geometry winding of silk fibroin in the collagen gel. A finite element model taking into account the orthotropic elasticity of arteries has been combined with classic laminate theory applied to the filament winding of a tubular vessel. The design of the small structure susceptible to scaffold the vascular tissue regeneration was optimised by mean of an evolutive algorithm with the imperative to mimic the experimentally measured mechanical properties (compliance) of a native artery.
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Demirkoparan, Hasan, and Jose Merodio. "Bulging bifurcation of inflated circular cylinders of doubly fiber-reinforced hyperelastic material under axial loading and swelling." Mathematics and Mechanics of Solids 22, no. 4 (September 6, 2015): 666–82. http://dx.doi.org/10.1177/1081286515600045.
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In this paper, we examine the influence of swelling on the bulging bifurcation of inflated thin-walled cylinders under axial loading. We provide the bifurcation criteria for a membrane cylinder subjected to combined axial loading, internal pressure and swelling. We focus here on orthotropic materials with two preferred directions which are mechanically equivalent and are symmetrically disposed. Arterial wall tissue is modeled with this class of constitutive equation and the onset of bulging is considered to give aneurysm formation. It is shown that swelling may lead to compressive hoop stresses near the inner radius of the tube, which could have a potential benefit for preventing aneurysm formation. The effects of the axial stretch, the strength of the fiber reinforcement and the fiber winding angle on the onset of bifurcation are investigated. Finally, a boundary value problem is studied to show the robustness of the results.
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Bhattarai, Aroj, Medisa Jabbari, Ralf Anding, and Manfred Staat. "Surgical treatment of vaginal vault prolapse using different prosthetic mesh implants: a finite element analysis." tm - Technisches Messen 85, no. 5 (May 25, 2018): 331–42. http://dx.doi.org/10.1515/teme-2017-0115.
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Abstract Particularly multiparous elderly women may suffer from vaginal vault prolapse after hysterectomy due to weak support from lax apical ligaments. A decreased amount of estrogen and progesterone in older age is assumed to remodel the collagen thereby reducing tissue stiffness. Sacrocolpopexy is either performed as open or laparoscopic surgery using prosthetic mesh implants to substitute lax ligaments. Y-shaped mesh models (DynaMesh, Gynemesh, and Ultrapro) are implanted in a 3D female pelvic floor finite element model in the extraperitoneal space from the vaginal cuff to the first sacral (S1) bone below promontory. Numerical simulations are conducted during Valsalva maneuver with weakened tissues modeled by reduced tissue stiffness. Tissues are modeled as incompressible, isotropic hyperelastic materials whereas the meshes are modeled either as orthotropic linear elastic or as isotropic hyperlastic materials. The positions of the vaginal cuff and the bladder base are calculated from the pubococcygeal line for female pelvic floor at rest, for prolapse and after repair using the three meshes. Due to mesh mechanics and mesh pore deformation along the loaded direction, the DynaMesh with regular rectangular mesh pores is found to provide better mechanical support to the organs than the Gynemesh and the Ultrapro with irregular hexagonal mesh pores.
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Li, Wenjie, Haiqian Xu, and Cheng Qian. "c-Kit-Positive Adipose Tissue-Derived Mesenchymal Stem Cells Promote the Growth and Angiogenesis of Breast Cancer." BioMed Research International 2017 (2017): 1–12. http://dx.doi.org/10.1155/2017/7407168.
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Background. Adipose tissue-derived mesenchymal stem cells (ASCs) improve the regenerative ability and retention of fat grafts for breast reconstruction in cancer patients following mastectomy. However, ASCs have also been shown to promote breast cancer cell growth and metastasis. For the safety of ASC application, we aimed to identify specific markers for the subpopulation of ASCs that enhance the growth of breast cancer.Methods. ASCs and bone marrow-derived vascular endothelial progenitor cells (EPCs) were isolated from Balb/c mice. c-Kit-positive (c-Kit+) or c-Kit-negative (c-Kit-) ASCs were cocultured with 4T1 breast cancer cells. Orthotropic murine models of 4T1, EPCs + 4T1, and c-Kit+/-ASCs + 4T1/EPCs were established in Balb/c mice.Results. In coculture, c-Kit+ASCs enhanced the viability and proliferation of 4T1 cells and stimulated c-Kit expression and interleukin-3 (IL-3) release. In mouse models, c-Kit+ASCs + 4T1/EPCs coinjection increased the tumor volume and vessel formation. Moreover, IL-3, stromal cell-derived factor-1, and vascular endothelial growth factor A in the c-Kit+ASCs + 4T1/EPCs coinjection group were higher than those in the 4T1, EPCs + 4T1, and c-Kit-ASCs + 4T1/EPCs groups.Conclusions. c-Kit+ASCs may promote breast cancer growth and angiogenesis by a synergistic effect of c-Kit and IL-3. Our findings suggest that c-Kit+subpopulations of ASCs should be eliminated in fat grafts for breast reconstruction of cancer patients following mastectomy.
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COLLI FRANZONE, PIERO, and LUCA F. PAVARINO. "A PARALLEL SOLVER FOR REACTION–DIFFUSION SYSTEMS IN COMPUTATIONAL ELECTROCARDIOLOGY." Mathematical Models and Methods in Applied Sciences 14, no. 06 (June 2004): 883–911. http://dx.doi.org/10.1142/s0218202504003489.
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In this work, a parallel three-dimensional solver for numerical simulations in computational electrocardiology is introduced and studied. The solver is based on the anisotropic Bidomain cardiac model, consisting of a system of two degenerate parabolic reaction–diffusion equations describing the intra and extracellular potentials of the myocardial tissue. This model includes intramural fiber rotation and anisotropic conductivity coefficients that can be fully orthotropic or axially symmetric around the fiber direction. The solver also includes the simpler anisotropic Monodomain model, consisting of only one reaction–diffusion equation. These cardiac models are coupled with a membrane model for the ionic currents, consisting of a system of ordinary differential equations that can vary from the simple FitzHugh–Nagumo (FHN) model to the more complex phase-I Luo–Rudy model (LR1). The solver employs structured isoparametric Q1finite elements in space and a semi-implicit adaptive method in time. Parallelization and portability are based on the PETSc parallel library. Large-scale computations with up to O(107) unknowns have been run on parallel computers, simulating excitation and repolarization phenomena in three-dimensional domains.
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Sonabend, Adam, Crismita Dmello, Li Chen, Victor A. Arrieta, Edgar Gonzalez, J. Robert Kane, Lisa Magnusson, et al. "SCIDOT-07. ULTRASOUND DELIVERED ALBUMIN BOUND PACLITAXEL EXTENDS SURVIVAL IN MALIGNANT GLIOMA MODELS AND OUTPERFORMS ULTRASOUND DELIVERED CREMOPHOR PACLITAXEL IN BIO-DISTRIBUTION AND SAFETY." Neuro-Oncology 21, Supplement_6 (November 2019): vi273—vi274. http://dx.doi.org/10.1093/neuonc/noz175.1148.
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Abstract Paclitaxel is anti-neoplastic agent shown to be extremely potent against glioblastoma in-vitro; however, it has yet to demonstrate antitumor activity in the clinic due to its inadequate brain penetration. Ultrasound-mediated drug delivery is an emerging new technology that transiently disrupts the blood-brain barrier to allow the passage of larger molecules that under physiological conditions would not reach the brain tissue. In this preclinical study, we investigated the ability of low intensity pulsed ultrasound (LIPU), delivered with the SonoCloud System (CarThera), to increase brain paclitaxel concentrations in a murine model. LIPU increased paclitaxel concentrations in the brain 300–500% after systemic administration of two different commercially available formulations of paclitaxel; paclitaxel dissolved in Cremophor (Taxol®) and albumin-bound paclitaxel (Abraxane®). The two formulations differed in their toxicity and biodistribution profiles with albumin-bound paclitaxel exhibiting increased tolerability and brain penetration. After sonication, albumin-bound paclitaxel increased survival in an orthotropic glioma model, whereas cremophor-paclitaxel induced central nervous system toxicity. Our experiments suggest that increased paclitaxel drug delivery by opening the BBB is feasible, and an effective anti-glioma treatment. Albumin-bound paclitaxel is the preferred formulation for further investigation with the SonoCloud system in the clinical setting.
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Tomlinson, P. B. "REACTION TISSUES IN GNETUM GNEMON A PRELIMINARY REPORT." IAWA Journal 22, no. 4 (2001): 401–13. http://dx.doi.org/10.1163/22941932-90000385.
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Gnetum gnemon exhibits Rouxʼs model of tree architecture, with clear differentiation of orthotropic from plagiotropic axes. All axes have similar anatomy and react to displacement in the same way. Secondary xylem of displaced stems shows little eccentricity of development and no reaction anatomy. In contrast, there is considerable eccentricity in extra-xylary tissue involving both primary and secondary production of apparent tension-wood fibres (gelatinous fibres) of three main kinds. Narrow primary fibres occur concentrically in all axes in the outer cortex as a normal developmental feature. In displaced axes gelatinous fibres are developed abundantly and eccentrically on the topographically upper side, from pre-existing and previously undetermined primary cortical cells. They are wide with lamellate cell walls. In addition narrow secondary phloem fibres are also differentiated abundantly and eccentrically on the upper side of displaced axes. These gelatinous fibres are narrow and without obviously lamellate cell walls. Eccentric gelatinous fibres thus occupy a position that suggests they have the function of tension wood fibres as found in angiosperms. This may be the first report in a gymnosperm of fibres with tension capability. Gnetum gne-mon thus exhibits reaction tissues of unique types, which are neither gymnospermous nor angiospermous. Reaction tissues seem important in maintaining the distinctive architecture of the tree.
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Ateshian, Gerard A. "Anisotropy of Fibrous Tissues in Relation to the Distribution of Tensed and Buckled Fibers." Journal of Biomechanical Engineering 129, no. 2 (September 29, 2006): 240–49. http://dx.doi.org/10.1115/1.2486179.
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Fibrous tissues are characterized by a much higher stiffness in tension than compression. This study uses microstructural modeling to analyze the material symmetry of fibrous tissues undergoing tension and compression, to better understand how material symmetry relates to the distribution of tensed and buckled fibers. The analysis is also used to determine whether the behavior predicted from a microstructural model can be identically described by phenomenological continuum models. The analysis confirms that in the case when all the fibers are in tension in the current configuration, the material symmetry of a fibrous tissue in the corresponding reference configuration is dictated by the symmetry of its fiber angular distribution in that configuration. However, if the strain field exhibits a mix of tensile and compressive principal normal strains, the fibrous tissue is represented by a material body which consists only of those fibers which are in tension; the material symmetry of this body may be deduced from the superposition of the planes of symmetry of the strain and the planes of symmetry of the angular fiber distribution. Thus the material symmetry is dictated by the symmetry of the angular distribution of only those fibers which are in tension. Examples are provided for various fiber angular distribution symmetries. In particular, it is found that a fibrous tissue with isotropic fiber angular distribution exhibits orthotropic symmetry when subjected to a mix of tensile and compressive principal normal strains, with the planes of symmetry normal to the principal directions of the strain. This anisotropy occurs even under infinitesimal strains and is distinct from the anisotropy induced from the finite rotation of fibers. It is also noted that fibrous materials are not stable under all strain states due to the inability of fibers to sustain compression along their axis; this instability can be overcome by the incorporation of a ground matrix. It is concluded that the material response predicted using a microstructural model of the fibers cannot be described exactly by phenomenological continuum models. These results are also applicable to nonbiological fiber–composite materials.
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Okada, Vaeteewoottacharn, and Kariya. "Application of Highly Immunocompromised Mice for the Establishment of Patient-Derived Xenograft (PDX) Models." Cells 8, no. 8 (August 13, 2019): 889. http://dx.doi.org/10.3390/cells8080889.
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Patient-derived xenograft (PDX) models are created by engraftment of patient tumor tissues into immunocompetent mice. Since a PDX model retains the characteristics of the primary patient tumor including gene expression profiles and drug responses, it has become the most reliable in vivo human cancer model. The engraftment rate increases with the introduction of Non-obese diabetic Severe combined immunodeficiency (NOD/SCID)-based immunocompromised mice, especially the NK-deficient NOD strains NOD/SCID/interleukin-2 receptor gamma chain(IL2Rγ)null (NOG/NSG) and NOD/SCID/Jak3(Janus kinase 3)null (NOJ). Success rates differ with tumor origin: gastrointestinal tumors acquire a higher engraftment rate, while the rate is lower for breast cancers. Subcutaneous transplantation is the most popular method to establish PDX, but some tumors require specific environments, e.g., orthotropic or renal capsule transplantation. Human hormone treatment is necessary to establish hormone-dependent cancers such as prostate and breast cancers. PDX mice with human hematopoietic and immune systems (humanized PDX) are powerful tools for the analysis of tumor–immune system interaction and evaluation of immunotherapy response. A PDX biobank equipped with patients’ clinical data, gene-expression patterns, mutational statuses, tumor tissue architects, and drug responsiveness will be an authoritative resource for developing specific tumor biomarkers for chemotherapeutic predictions, creating individualized therapy, and establishing precise cancer medicine.
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Niebur, Glen L., Michael J. Feldstein, and Tony M. Keaveny. "Biaxial Failure Behavior of Bovine Tibial Trabecular Bone." Journal of Biomechanical Engineering 124, no. 6 (December 1, 2002): 699–705. http://dx.doi.org/10.1115/1.1517566.
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Multiaxial failure properties of trabecular bone are important for modeling of whole bone fracture and can provide insight into structure-function relationships. There is currently no consensus on the most appropriate form of multiaxial yield criterion for trabecular bone. Using experimentally validated, high-resolution, non-linear finite element models, biaxial plain strain boundary conditions were applied to seven bovine tibial specimens. The dependence of multiaxial yield properties on volume fraction was investigated to quantify the interspecimen heterogeneity in yield stresses and strains. Two specimens were further analyzed to determine the yield properties for a wide range of biaxial strain loading conditions. The locations and quantities of tissue level yielding were compared for on-axis, transverse, and biaxial apparent level yielding to elucidate the micromechanical failure mechanisms. As reported for uniaxial loading of trabecular bone, the yield strains in multiaxial loading did not depend on volume fraction, whereas the yield stresses did. Micromechanical analysis indicated that the failure mechanisms in the on-axis and transverse loading directions were mostly independent. Consistent with this, the biaxial yield properties were best described by independent curves for on-axis and transverse loading. These findings establish that the multiaxial failure of trabecular bone is predominantly governed by the strain along the loading direction, requiring separate analytical expressions for each orthotropic axis to capture the apparent level yield behavior.
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Rastgar Agah, Mobin, Kaveh Laksari, Soroush Assari, and Kurosh Darvish. "Mechanical behavior of porcine thoracic aorta in physiological and supra-physiological intraluminal pressures." Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine 231, no. 4 (March 23, 2017): 326–36. http://dx.doi.org/10.1177/0954411917695577.
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Understanding the mechanical behavior of aorta under supra-physiological loadings is an important aspect of modeling tissue behavior in various applications that involve large deformations. Utilizing inflation–extension experiments, the mechanical behavior of porcine descending thoracic aortic segments under physiological and supra-physiological intraluminal pressures was investigated. The pressure was changed in the range of 0–70 kPa and the deformation of the segment was determined in three dimensions using a custom-made motion capture system. An orthotropic Fung-type constitutive model was characterized by implementing a novel computationally efficient framework that ensured material stability for numerical simulations. The nonlinear rising trend of circumferential stretch ratio [Formula: see text] from outer toward inner wall was significantly increased at higher pressures. The increase in [Formula: see text] from physiological pressure (13 kPa) to 70 kPa was 13% at the outer wall and 22% at the inner wall; in this pressure range, the longitudinal stretch ratio [Formula: see text] increased 20%. A significant nonlinearity in the material behavior was observed as in the same pressure range, and the circumferential and longitudinal Cauchy stresses at the inner wall were increased 16 and 18 times, respectively. The overall constitutive model was verified in several loading paths in the [Formula: see text] space to confirm its applicability in multi-axial loading conditions.
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Lucci, Giulio, and Luigi Preziosi. "A nonlinear elastic description of cell preferential orientations over a stretched substrate." Biomechanics and Modeling in Mechanobiology 20, no. 2 (January 15, 2021): 631–49. http://dx.doi.org/10.1007/s10237-020-01406-4.
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AbstractThe active response of cells to mechanical cues due to their interaction with the environment has been of increasing interest, since it is involved in many physiological phenomena, pathologies, and in tissue engineering. In particular, several experiments have shown that, if a substrate with overlying cells is cyclically stretched, they will reorient to reach a well-defined angle between their major axis and the main stretching direction. Recent experimental findings, also supported by a linear elastic model, indicated that the minimization of an elastic energy might drive this reorientation process. Motivated by the fact that a similar behaviour is observed even for high strains, in this paper we address the problem in the framework of finite elasticity, in order to study the presence of nonlinear effects. We find that, for a very large class of constitutive orthotropic models and with very general assumptions, there is a single linear relationship between a parameter describing the biaxial deformation and $$\cos ^2\theta _{\mathrm{eq}}$$ cos 2 θ eq , where $$\theta _{\mathrm{eq}}$$ θ eq is the orientation angle of the cell, with the slope of the line depending on a specific combination of four parameters that characterize the nonlinear constitutive equation. We also study the effect of introducing a further dependence of the energy on the anisotropic invariants related to the square of the Cauchy–Green strain tensor. This leads to departures from the linear relationship mentioned above, that are again critically compared with experimental data.
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Hofstetter, Karin, Christian Hellmich, and Josef Eberhardsteiner. "Micromechanical modeling of solid-type and plate-type deformation patterns within softwood materials. A review and an improved approach." Holzforschung 61, no. 4 (June 1, 2007): 343–51. http://dx.doi.org/10.1515/hf.2007.058.
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Abstract Wood exhibits a highly diverse microstructure. It appears as a solid-type composite material at a length scale of some micrometers, while it resembles an assembly of plate-like elements arranged in a honeycomb fashion at the length scale of some hundreds of micrometers. These structural features result in different load-carrying mechanisms at different observation scales and under different loading conditions. In this paper, we elucidate the main load-carrying mechanisms by means of a micromechanical model for softwood materials. Representing remarkable progress with respect to earlier models reported in the literature, this model is valid across various species. The model is based on tissue-independent stiffness properties of cellulose, lignin, hemicellulose, and water obtained from direct testing and lattice-dynamics analyses. Sample-specific characteristics are considered in terms of porosity and the contents of cellulose, lignin, hemicelluloses and water, which are obtained from mass density measurements, environmental scanning micrographs, analytical chemistry, and NMR spectroscopy. The model comprises three homogenization steps, two based on continuum micromechanics and one on the unit cell method. The latter represents plate-like bending and shear of the cell walls due to transverse shear loading and axial straining in the tangential stem direction. Accurate representation of these deformation modes results in accurate (orthotropic) stiffness estimates across a variety of softwood species. These stiffness predictions deviate, on average, by less than 10% from corresponding experimental results obtained from ultrasonic or quasi-static testing. Thus, the proposed model can reliably predict microscopic and macroscopic mechanical properties from internal structure and composition, and is therefore expected to significantly support wood production technology (such as drying techniques) and mechanical analyses of timber structures.
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Daghighi, A., H. Tropp, N. Dahlström, and A. Klarbring. "F.E.M. Stress-Investigation of Scolios Apex." Open Biomedical Engineering Journal 12, no. 1 (July 31, 2018): 51–71. http://dx.doi.org/10.2174/1874120701812010051.
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Background:In scoliosis, kypholordos and wedge properties of the vertebrae should be involved in determining how stress is distributed in the vertebral column. The impact is logically expected to be maximal at the apex.Aim:To introduce an algorithm for constructing artificial geometric models of the vertebral column from DICOM stacks, with the ultimate aim to obtain a formalized way to create simplistic models, which enhance and focus on wedge properties and relative tilting.Material/Methods:Our procedure requires parameter extraction from DICOM image-stacks (with PACS,IDS-7), mechanical FEM-modelling (with Matlab and Comsol). As a test implementation, models were constructed for five patients with thoracal idiopathic scoliosis with varying apex rotation. For a selection of load states, we calculated a response variable which is based upon distortion energy.Results:For the test implementation, pairwise t-tests show that our response variable is non-trivial and that it is chiefly sensitive to the transversal stresses (transversal stresses where of main interest to us, as opposed to the case of additional shear stresses, due to the lack of explicit surrounding tissue and ligaments in our model). Also, a pairwise t-test did not show a difference (n = 25, p-value≈0.084) between the cases of isotropic and orthotropic material modeling.Conclusion:A step-by-step description is given for a procedure of constructing artificial geometric models from chest CT DICOM-stacks, such that the models are appropriate for semi-global stress-analysis, where the focus is on the wedge properties and relative tilting. The method is inappropriate for analyses where the local roughness and irregularities of surfaces are wanted features. A test application hints that one particular load state possibly has a high correlation to a certain response variable (based upon distortion energy distribution on a surface of the apex), however, the number of patients is too small to draw any statistical conclusions.
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Pistoia, W., B. van Rietbergen, A. Laib, and P. Ru¨egsegger. "High-Resolution Three-Dimensional-pQCT Images Can Be an Adequate Basis for In-Vivo μFE Analysis of Bone." Journal of Biomechanical Engineering 123, no. 2 (October 1, 2000): 176–83. http://dx.doi.org/10.1115/1.1352734.
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Micro-finite element (μFE) models based on high-resolution images have enabled the calculation of elastic properties of trabecular bone in vitro. Recently, techniques have been developed to image trabecular bone structure in vivo, albeit at a lesser resolution. The present work studies the usefulness of such in-vivo images for μFE analyses, by comparing their μFE results to those of models based on high-resolution micro-CT (μCT) images. Fifteen specimens obtained from human femoral heads were imaged first with a 3D-pQCT scanner at 165 μm resolution and a second time with a μCT scanner at 56 μm resolution. A third set of images with a resolution of 165 μm was created by downscaling the μCT measurements. The μFE models were created directly from these images. Orthotropic elastic properties and the average tissue von Mises stress of the specimens were calculated from six FE-analyses per specimen. The results of the 165 μm models were compared to those of the 56 μm model, which was taken as the reference model. The results calculated from the pQCT-based models, correlated excellent with those calculated from the reference model for both moduli R2>0.95 and for the average tissue von Mises stress R2>0.83. Results calculated from the downscaled micro-CT models correlated even better with those of the reference models (R2>0.99 for the moduli and R2>0.96 for the average von Mises stress). In the case of the 3D-pQCT based models, however, the slopes of the regression lines were less than one and had to be corrected. The prediction of the Poisson’s ratios was less accurate (R2>0.45 and R2>0.67) for the models based on 3D-pQCT and downscaled μCT images respectively). The fact that the results from the downscaled and original μCT images were nearly identical indicates that the need for a correction in the case of the 3D-pQCT measurements was not due to the voxel size of the images but due to a higher noise level and a lower contrast in these images, in combination with the application of a filtering procedure at 165 micron images. In summary: the results of μFE models based on in-vivo images of the 3D-pQCT can closely resemble those obtained from μFE models based on higher resolution μCT system.
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Dhandapani, Natesan, A. Gnanavelbabu, and M. Sivasankar. "Failure Analysis of Cementless Hip Joint Prosthesis." Advanced Materials Research 845 (December 2013): 403–7. http://dx.doi.org/10.4028/www.scientific.net/amr.845.403.
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In this changing global scenario, modification, transplantation, and replacement can be the eternal solution for most of the problems in the medical field. Hence replacement technique finds a very prominent place in medicine as a remedy having closely tied up with biomechanics. One of the most important joints in the human body is the hip joint, the big and complex joint. Many researches were conducted and many are in progress, but most of these works use simplified models with either 2D or 3D approaches. The hip joint is formed by four components like femoral head cortical bone, stem, and neck. In this system we can find orthotropic and isotropic materials working together. The main objective of this research is to develop a three dimensional surface and solid finite element model of the hip joint to predict stresses in its individual components. This model is a geometric non-linear model, which helps us understand its structural mechanical behavior, seeming to suggest with advanced research in the future new hip joint prosthesis, as well as to prove the prosthesis joint interaction before being implanted in the patient. This research explains a complete human hip joint model without cartilaginous tissue, using ANSYS 10.0 Multiphysics Analysis for nine different postures in hip joint using three different materials (CoCr, Ti6Al4V, and UHMWPE) to calculate fatigue life. The result obtained from the analysis of surface model and solid model serve to help in predicting the life cycle, surface characteristics, shear stress in XY plane, stress concentration and areas that are prone to failure. Von Mises stress on the surface of our model facilitates us to equip and design an optimized prosthesis device having unique materials composition , with a highly bio-compatible and durable alloy at a low cost could be produced. In this way, a first important step towards the structural characterization of human hip joint has been developed.
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Kao, Philip H., Steven R. Lammers, Lian Tian, Kendall Hunter, Kurt R. Stenmark, Robin Shandas, and H. Jerry Qi. "A Microstructurally Driven Model for Pulmonary Artery Tissue." Journal of Biomechanical Engineering 133, no. 5 (April 8, 2011). http://dx.doi.org/10.1115/1.4002698.
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A new constitutive model for elastic, proximal pulmonary artery tissue is presented here, called the total crimped fiber model. This model is based on the material and microstructural properties of the two main, passive, load-bearing components of the artery wall, elastin, and collagen. Elastin matrix proteins are modeled with an orthotropic neo-Hookean material. High stretch behavior is governed by an orthotropic crimped fiber material modeled as a planar sinusoidal linear elastic beam, which represents collagen fiber deformations. Collagen-dependent artery orthotropy is defined by a structure tensor representing the effective orientation distribution of collagen fiber bundles. Therefore, every parameter of the total crimped fiber model is correlated with either a physiologic structure or geometry or is a mechanically measured material property of the composite tissue. Further, by incorporating elastin orthotropy, this model better represents the mechanics of arterial tissue deformation. These advancements result in a microstructural total crimped fiber model of pulmonary artery tissue mechanics, which demonstrates good quality of fit and flexibility for modeling varied mechanical behaviors encountered in disease states.
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Kim, GeunHyung, and WanDoo Kim. "Designed PCL Nanofibers Fabricated Using a Modified Electrohydrodynamic Process for Tissue Engineering." Journal of Manufacturing Science and Engineering 130, no. 2 (March 20, 2008). http://dx.doi.org/10.1115/1.2896108.
Full textAbstract:
An ideal scaffold should have good mechanical properties and provide a biologically functional implant site. Considering their large surface area, high porosity, and good interconnectivity of pores, electrospun micro-∕nanofibers have good potential as biomimic scaffolds. In this study, various poly(ε-carprolactone) webs consisting of uniaxially oriented micro-∕nanofibers were produced using an electrohydrodynamic process (electrospinning) with a conical electrode and two-axis collector. The oriented fibrous web showed mechanical orthotropic properties, which might be important for designing engineering scaffolds that mimic natural tissues, such as a blood vessel or ligament, which have orthotropic mechanical properties. In addition, the fabricated mats, which were electrospun using computer-assisted design, had good hydrophilic and good cellular behavior compared to a random fiber mat.