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CONTENTS
Volume 1, Number 2, June 2014
 

Abstract
Creep phenomenon at the scale of bone tissue (small specimens) is known to be present and demonstrated for low strains. Here creep is demonstrated on a pair of fresh-frozen human femurs at the organ level at high strains. Under a constant displacement applied on femur\'s head, surface strains at the upper neck location increase with time until fracture, that occurs within 7-13 seconds. The monotonic increase in strains provides evidence on damage accumulation in the interior (probably damage to the trabeculae) prior to final fracture, a fact that hints on probable damage of the trabecular bone that occurs prior to the catastrophic fracture of the cortical surface layer.

Key Words
femur; fracture; creep

Address
Zohar Yosibash and Romina Plitman Mayo: Department of Mechanical Engineering, Ben-Gurion University of the Negev, Beer-Sheva, 84105, Israel
Charles Milgrom: Hadassah Hospital and Hebrew University of Jerusalem, Ein-Kerem, Jerusalem, Israel

Abstract
In this paper, two procedures of enumerating the axial rotation are proposed using the unit sphere of the spherical rotation coordinate system specifying 3D rotation. If the trajectory of the movement is known, the integration of the axial component of the angular velocity plus the geometric effect equal to the enclosed area subtended by the geodesic path on the surface of the unit sphere. If the postures of the initial and final positions are known, the axial rotation is determined by the angular difference from the parallel transport along the geodesic path. The path dependency of the axial rotation of the three dimensional rigid body motion is due to the geometric effect corresponding to the closed loop discontinuity. Firstly, the closed loop discontinuity is examined for the infinitesimal region. The general closed loop discontinuity can be evaluated by the summation of those discontinuities of the infinitesimal regions forming the whole loop. This general loop discontinuity is equal to the surface area enclosed by the closed loop on the surface of the unit sphere. Using this quantification of the closed loop discontinuity of the axial rotation, the geometric effect is determined in enumerating the axial rotation. As an example, the axial rotation of the arm by the Codman

Key Words
axial rotation; geometric phase; prime geodesic; Codman

Address
Yong-San Yoon: Mechanical Engineering, Korea Advanced Institute of Science & Technology, Yuseong-ku, Daejeon 305-701, Korea

Abstract
Peri-acetabular bone ingrowth plays a crucial role in long-term stability of press-fit acetabular cups. A poor bone ingrowth often results in increased cup migration, leading to aseptic loosening of the implant. The rate of peri-prosthetic bone formation is also affected by the polar gap that may be introduced during implantation. Applying a mechano-regulatory tissue differentiation algorithm on a two-dimensional plane strain microscale model, representing implant-bone interface, the objectives of the study are to gain an insight into the process of peri-prosthetic tissue differentiation and to investigate its relationship with implant-bone relative displacement and size of the polar gap. Implant-bone relative displacement was found to have a considerable influence on bone healing and peri-acetabular bone ingrowth. An increase in implant-bone relative displacement from 20

Key Words
tissue differentiation; bone ingrowth; acetabular polar gap; bone healing; finite element analysis

Address
Kaushik Mukherjee and Sanjay Gupta: Department of Mechanical Engineering, Indian Institute of Technology Kharagpur, Kharagpur 721302, West Bengal, India


Abstract
The microarchitecture of trabecular bone plays a significant role in mechanical strength due to its load-bearing capability. However, the complexity of trabecular microarchitecture hinders the evaluation of its morphological characteristics. We therefore propose a new classification method based on static multiscale theory and dynamic finite element method (FEM) analysis to visualize a three-dimensional (3D) trabecular network for investigating the influence of trabecular microarchitecture on load-bearing capability. This method is applied to human vertebral trabecular bone images obtained by micro-computed tomography (micro-CT) through which primary trabecular bone is successfully visualized and extracted from a highly complicated microarchitecture. The morphological features were then analyzed by viewing the percolation of load pathways in the primary trabecular bone by using the stress wave propagation method analyzed under impact loading. We demonstrate that the present method is effective for describing the morphology of trabecular bone and has the potential for morphometric measurement applications.

Key Words
vertebra; trabecular network; morphology; image-based modeling; homogenization method; dynamic FEM

Address
Khairul Salleh Basaruddin: School of Mechatronic Engineering, Universiti Malaysia Perlis, 02600 Pauh Putra, Perlis, Malaysia
Junya Omori: Graduate School of Science and Technology, Keio University, 3-14-1 Hiyoshi, Yokohama, 223-8522, Japan
Naoki Takano: Department of Mechanical Engineering, Keio University, 3-14-1 Hiyoshi, Yokohama, 223-8522, Japan
Takayoshi Nakano: Division of Materials and Manufacturing Science, Osaka University, 2-1,Suita, Osaka 565-0871, Japan

Abstract
A preliminary study of a new pulsatile pump that will work to a frequency greater than 1 Hz, is presented. The fluid-structure interaction between a Newtonian blood flow and a piston drive that moves with periodic speed is simulated. The mechanism is of double effect and has four valves, two at the input flow and two at the output flow; the valves are simulated with specified velocity of closing and reopening. The simulation is made with finite elements software named COMSOL Multiphysics 3.3 to resolve the flow in a preliminary planar configuration. The geometry is 2D to determine areas of high speeds and high shear stresses that can cause hemolysis and platelet aggregation. The opening and closing valves are modelled by solid structure interacting with flow, the rhythmic opening and closing are synchronized with the piston harmonic movement. The boundary conditions at the input and output areas are only normal traction with reference pressure. On the other hand, the fluid structure interactions are manifested due to the non-slip boundary conditions over the piston moving surfaces, moving valve contours and fix pump walls. The non-physiologic frequency pulsatile pump, from the viewpoint of fluid flow analysis, is predicted feasible and with characteristic of low hemolysis and low thrombogenesis, because the stress tension and resident time are smaller than the limit and the vortices are destroyed for the periodic flow.

Key Words
ventricular assist pump; blood flow; fluid structure interaction; finite element method; cardiac insufficiency

Address
Jose Di Paolo, Jordan F. Insfran, Exequiel R. Fries, Diego M. Campana, Marcelo E. Berli and Sebastian Ubal: Computational Biomechanics Group, Engineering Faculty, National University of Entre Rios Ruta 11, km 10, 3100 Oro Verde, Entre Rios, Argentina



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