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Finite element modeling

Asif Rahman, Belen Lafon, Lucas C Parra, Marom Bikson
KEY POINTS: Direct current stimulation (DCS) polarity specifically modulates synaptic efficacy during a continuous train of presynaptic inputs, despite synaptic depression. DCS polarizes afferent axons and postsynaptic neurons, boosting cooperativity between synaptic inputs. Polarization of afferent neurons in upstream brain regions may modulate activity in the target brain region during transcranial DCS (tDCS). A statistical theory of coincident activity predicts that the diffuse and weak profile of current flow can be advantageous in enhancing connectivity between co-active brain regions...
April 23, 2017: Journal of Physiology
Mojtaba Mahmoudi, Ali Reza Saidi, Parviz Amini, Maryam Alsadat Hashemipour
STATEMENT OF PROBLEM: In post-core crown restorations, the use of flexible posts concentrates stresses at the dentin and the use of stiff posts concentrates stresses at the interfaces. A class of inhomogeneous materials (called functionally graded materials) has been proposed for posts to resolve the weaknesses of both flexible and rigid posts. PURPOSE: The purpose of this in vitro study was to design an inhomogeneous post and investigate its influence on the stress distribution of post-core crown restorations...
April 20, 2017: Journal of Prosthetic Dentistry
E Galvin, D O'Brien, C Cummins, B J Mac Donald, C Lally
This paper presents a strain-mediated phenomenological corrosion model, based on the discrete finite element modelling method which was developed for use with the ANSYS Implicit finite element code. The corrosion model was calibrated from experimental data and used to simulate the corrosion performance of a WE43 magnesium alloy stent. The model was found to be capable of predicting the experimentally observed plastic strain-mediated mass loss profile. The non-linear plastic strain model, extrapolated from the experimental data, was also found to adequately capture the corrosion-induced reduction in the radial stiffness of the stent over time...
April 19, 2017: Acta Biomaterialia
Yuan Feng, Suhao Qiu, Xiaolong Xia, Songbai Ji, Chung-Hao Lee
The aligned axonal fiber bundles in white matter make it suitable to be modeled as a transversely isotropic material. Recent experimental studies have shown that a minimal form, nearly incompressible transversely isotropic (MITI) material model, is capable of describing mechanical anisotropy of white matter. Here, we used a finite element (FE) computational approach to demonstrate the significance of the fifth invariant (I5) when modeling the anisotropic behavior of white matter in the large-strain regime. We first implemented and validated the MITI model in an FE simulation framework for large deformations...
April 9, 2017: Journal of Biomechanics
Ranajay Ghosh, Hamid Ebrahimi, Ashkan Vaziri
Biomimetic scales are known to substantially alter the mechanics response of the underlying substrate engendering complex nonlinearities that can manifest even in small deformations due to scales interaction. This interaction is typically modeled using a-priori homogenization with an enforced periodicity of engagement. Such a framework is fairly useful especially when dealing with the structural length scale which is at least one order of magnitude greater than the scales themselves since individual tracking of a large number of scales become insurmountable...
April 15, 2017: Journal of the Mechanical Behavior of Biomedical Materials
Éva Sautner, Krisztián Papp, Eszter Holczer, Eszter L Tóth, Rita Ungai-Salánki, Bálint Szabó, Péter Fürjes, József Prechl
Microfluidic devices exploit combined physical, chemical and biological phenomena that could be unique in the sub-millimeter dimensions. The current goal of development of Point-of-Care (POC) medical devices is to extract the biomedical information from the blood. We examined the characteristics of blood flow in autonomous microfluidic devices with the aim to realize sensitive detection of interactions between particulate elements of the blood and the appropriately modified surfaces of the system. As a model experiment we demonstrated the fast analysis of the AB0 blood group system...
April 21, 2017: Scientific Reports
Jeffrey Mason Earles, Guillaume Théroux-Rancourt, Matthew E Gilbert, Andrew J McElrone, Craig Brodersen
In agricultural and natural systems, diffuse light can enhance plant primary productivity due to deeper penetration into and greater illumination of the entire canopy. However, for individual sun-grown leaves from three species, photosynthesis is actually less efficient under diffuse compared to direct light. Despite its potential impact on canopy-level productivity, the mechanism for this leaf-level 'diffuse light photosynthetic depression' effect is unknown. Here we investigate if the spatial distribution of light absorption relative to electron transport capacity in sun- and shade-grown H...
April 21, 2017: Plant Physiology
Dong Ren, Yueju Liu, Xianchao Zhang, Zhaohui Song, Jian Lu, Pengcheng Wang
BACKGROUND: A three-dimensional finite element model (FEM) of the knee joint was established to analyze the biomechanical functions of the superficial and deep medial collateral ligaments (MCLs) of knee joints and to investigate the treatment of the knee medial collateral ligament injury. METHODS: The right knee joint of a healthy male volunteer was subjected to CT and MRI scans in the extended position. The scanned data were imported into MIMICS, Geomagic, and ANSYS software to establish a three-dimensional FEM of the human knee joint...
April 21, 2017: Journal of Orthopaedic Surgery and Research
Recep M Gorguluarslan, Seung-Kyum Choi, Christopher J Saldana
A methodology is proposed for uncertainty quantification and validation to accurately predict the mechanical response of lattice structures used in the design of scaffolds. Effective structural properties of the scaffolds are characterized using a developed multi-level stochastic upscaling process that propagates the quantified uncertainties at strut level to the lattice structure level. To obtain realistic simulation models for the stochastic upscaling process and minimize the experimental cost, high-resolution finite element models of individual struts were reconstructed from the micro-CT scan images of lattice structures which are fabricated by selective laser melting...
April 12, 2017: Journal of the Mechanical Behavior of Biomedical Materials
Biao Feng, Valery I Levitas
The main principles of producing a region near the center of a sample, compressed in a diamond anvil cell (DAC), with a very high pressure gradient and, consequently, with high pressure are predicted theoretically. The revealed phenomenon of generating extremely high pressure gradient is called the pressure self-focusing effect. Initial analytical predictions utilized generalization of a simplified equilibrium equation. Then, the results are refined using our recent advanced model for elastoplastic material under high pressures in finite element method (FEM) simulations...
April 21, 2017: Scientific Reports
Chung-Hao Lee, Will Zhang, Kristen Feaver, Robert C Gorman, Joseph H Gorman, Michael S Sacks
There continues to be a critical need for developing data-informed computational modeling techniques that enable systematic evaluations of mitral valve (MV) function. This is important for a better understanding of MV organ-level biomechanical performance, in vivo functional tissue stresses, and the biosynthetic responses of MV interstitial cells (MVICs) in the normal, pathophysiological, and surgically repaired states. In the present study, we utilized extant ovine MV population-averaged 3D fiducial marker data to quantify the MV anterior leaflet (MVAL) deformations in various kinematic states...
April 20, 2017: Biomechanics and Modeling in Mechanobiology
Satoshi Yamaguchi, Yasufumi Yamanishi, Lucas S Machado, Shuji Matsumoto, Nick Tovar, Paulo G Coelho, Van P Thompson, Satoshi Imazato
PURPOSE: The aim of this study was to evaluate fatigue resistance of dental fixtures with two different fixture-abutment connections by in vitro fatigue testing and in silico three-dimensional finite element analysis (3D FEA) using original computer-aided design (CAD) models. METHODS: Dental implant fixtures with external connection (EX) or internal connection (IN) abutments were fabricated from original CAD models using grade IV titanium and step-stress accelerated life testing was performed...
April 17, 2017: Journal of Prosthodontic Research
Batbayar Khuyagbaatar, Kyungsoo Kim, Won Man Park, Yoon Hyuk Kim
Post-operative C5palsies are among the most common complications seen after cervical surgery for ossification of the posterior longitudinal ligament (OPLL). Although C5 palsy is a well-known complication of cervical spine surgery, its pathogenesis is poorly understood and depends on many other factors. In this study, a finite element model of the cervical spine and spinal cord-nerve roots complex structures was developed. The changes in stress in the cord and nerve roots, posterior shift of the spinal cord, and displacement and elongation of the nerve roots after laminectomy for cervical OPLL were analyzed for three different cervical sagittal alignments (lordosis, straight, and kyphosis)...
April 5, 2017: Journal of Biomechanics
Lorenza Petrini, Alessandro Bertini, Francesca Berti, Giancarlo Pennati, Francesco Migliavacca
Nickel-titanium alloys are commonly adopted for producing cardiovascular minimally invasive devices such as self-expandable stents, aortic valves and stent-grafts. These devices are subjected to cyclic loads (due to blood pulsatility, leg or heart movements), that can induce fatigue fracture, and may also be subjected to very large deformations (due to crimping procedure, a tortuous physiological path or overloads), that can induce material yield. Recently, the authors developed a new constitutive model that considers inelastic strains due to not-completed reverse phase transformation (not all the stress-induced martensite turns back to austenite) or/and plasticity and their accumulation during cyclic loads...
May 2017: Proceedings of the Institution of Mechanical Engineers. Part H, Journal of Engineering in Medicine
Jing Zhang, Zhenxian Chen, Ling Wang, Dichen Li, Zhongmin Jin
Tibiofemoral contact forces in total knee replacement have been measured at the medial and lateral sites respectively using an instrumented prosthesis, and predicted from musculoskeletal multibody dynamics models with a reasonable accuracy. However, it is uncommon that the medial and lateral forces are applied separately to replace a total axial load according to the ISO standard in the majority of current finite element analyses. In this study, we quantified the different effects of applying the medial and lateral loads separately versus the traditional total axial load application on contact mechanics and wear prediction of a patient-specific knee prosthesis...
May 2017: Proceedings of the Institution of Mechanical Engineers. Part H, Journal of Engineering in Medicine
Francesc Levrero-Florencio, Krishnagoud Manda, Lee Margetts, Pankaj Pankaj
Micro-finite element models have been extensively employed to evaluate the elastic properties of trabecular bone and, to a limited extent, its yield behaviour. The macroscopic stiffness tensor and yield surface are of special interest since they are essential in the prediction of bone strength and stability of implants at the whole bone level. While macroscopic elastic properties are now well understood, yield and post-yield properties are not. The aim of this study is to shed some light on what the effect of the solid phase yield criterion is on the macroscopic yield of trabecular bone for samples with different microstructure...
May 2017: Proceedings of the Institution of Mechanical Engineers. Part H, Journal of Engineering in Medicine
Sandro D Badilatti, Patrik Christen, Stephen J Ferguson, Ralph Müller
Cement augmentation in vertebrae (vertebroplasty) is usually used to restore mechanical strength after spinal fracture but could also be used as a prophylactic treatment. So far, the mechanical competence has been determined immediately post-treatment, without considering long-term effects of bone adaptation. In this work, we investigated such long-term effects of vertebroplasty on the stiffness of the augmented bone by means of computational simulation of bone adaptation. Using micro-finite element analysis, we determined sites of increased mechanical stress (stress raisers) and stress shielding and, based on the simulations, regions with increased or decreased bone loss due to augmentation...
May 2017: Proceedings of the Institution of Mechanical Engineers. Part H, Journal of Engineering in Medicine
Suhas Somnath, Stephen Jesse, Gary J Van Berkel, Sergei V Kalinin, Olga S Ovchinnikova
The key to advancing materials is to understand and control their structure and chemistry. However, thorough chemical characterization is challenging since existing techniques characterize only a few properties of the specimen, thereby necessitating multiple measurement platforms to acquire the necessary information. The multimodal combination of atomic force microscopy (AFM) and mass spectrometry (MS) transcends existing analytical capabilities for nanometer scale spatially resolved correlation of the chemical and physical properties of a sample surface...
April 20, 2017: Nanoscale
Boyce E Griffith, Xiaoyu Luo
The immersed boundary method is an approach to fluid-structure interaction that uses a Lagrangian description of the structural deformations, stresses, and forces along with an Eulerian description of the momentum, viscosity, and incompressibility of the fluid-structure system. The original immersed boundary methods described immersed elastic structures using systems of flexible fibers, and even now, most immersed boundary methods still require Lagrangian meshes that are finer than the Eulerian grid. This work introduces a coupling scheme for the immersed boundary method to link the Lagrangian and Eulerian variables that facilitates independent spatial discretizations for the structure and background grid...
April 20, 2017: International Journal for Numerical Methods in Biomedical Engineering
Dequan Zhang, Xu Han, Zhongpu Zhang, Jie Liu, Chao Jiang, Nobuhiro Yoda, Xianghua Meng, Qing Li
Dynamic load exists in numerous biomechanical systems and its identification signifies a critical issue for characterizing dynamic behaviors and studying biomechanical consequence of the systems. This study aims to identify dynamic load in the dental prosthetic structures, namely three-unit implant-supported fixed partial denture (I-FPD) and teeth-supported fixed partial denture (T-FPD). The three-dimensional (3D) finite element (FE) models were constructed through patient's computerized tomography (CT) images...
April 20, 2017: International Journal for Numerical Methods in Biomedical Engineering
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