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2015 | Buch

Biomedical Technology

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Über dieses Buch

During the last years computational methods lead to new approaches that can be applied within medical practice. Based on the tremendous advances in medical imaging and high-performance computing, virtual testing is able to help in medical decision processes or implant designs. Current challenges in medicine and engineering are related to the application of computational methods to clinical medicine and the study of biological systems at different scales.

Additionally manufacturers will be able to use computational tools and methods to predict the performance of their medical devices in virtual patients. The physical and animal testing procedures could be reduced by virtual prototyping of medical devices. Here simulations can enhance the performance of alternate device designs for a range of virtual patients. This will lead to a refinement of designs and to safer products.

This book summarizes different aspects of approaches to enhance function, production, initialization and complications of different types of implants and related topics.

Inhaltsverzeichnis

Frontmatter
RVE Procedure for Estimating the Elastic Properties of Inhomogeneous Microstructures Such as Bone Tissue
Abstract
Cancellous bone can roughly be seen as a two-phase material consisting of the bone tissue reinforcement and the interstitial bone marrow matrix. Thus, for a computer-aided mechanical stress analysis of bones a constitutive law is required, which can predict the inhomogeneous elasticity depending on the local bone density and microstructure. Besides several measurement methods, the method of representative volume element (RVE) in combination with the finite element solution technique has been established for this purpose. This work investigates this method in detail. Therefore, random but statistical equivalent RVEs are created to have unlimited access to different structures. Generally, an apparent and not an effective stiffness is obtained due to the RVE method. However, a very close solution can be achieved if several issues are considered carefully. These issues can be divided into the set of boundary conditions, the RVE size and averaging the randomness. The influences are investigated accurately. A new approach is proposed to deduce an isotropic constitutive law from the anisotropic stiffness matrix. There are unlimited possible solutions in theory. However, the Voigt and Reuss approximations give the possible bounds. A method is described, which allows to obtain the effective stiffness by merging these bounds. A structural analysis is performed with different RVEs and the effective stiffness is estimated for varying parameters. An empirical equation is introduced, which covers the whole stiffness range. Therein, the microstructure is modelled with a single parameter. Real bone measurements can be fitted with this equation as well.
Tanja Blöß, Michael Welsch
A Gradient-Enhanced Continuum Damage Model for Residually Stressed Fibre-Reinforced Materials at Finite Strains
Abstract
The modelling of damage effects in materials constitutes a major challenge in various engineering-related disciplines. However, the assumption of purely local continuum damage formulations may lead to ill-posed boundary value problems and—with regard to numerical methods such as the finite element method—to mesh-dependent solutions, a vanishing localised damage zone upon mesh refinement, and hence physically questionable results. In order to circumvent these deficiencies, we present a non-local gradient-enhanced damage model at finite strains. We additively compose the hyperelastic constitutive response at local material point level of an isotropic matrix and of an anisotropic fibre-reinforced material. The inelastic constitutive response is characterised by a scalar [1– d]-damage model, where we assume only the anisotropic elastic part to damage. Furthermore, we enhance the local free energy by a gradient-term. This term essentially contains the gradient of the non-local damage variable which we introduce as an additional global field variable. In order to guarantee the equivalence between the local and non-local damage variable, we incorporate a penalisation term within the free energy. Based on the principle of minimum total potential energy, we obtain a coupled system of variational equations. The associated non-linear system of equations is symmetric and can conveniently be solved by standard incremental-iterative Newton-Raphson schemes or arc-length-based solution methods. As a further key aspect, we incorporate residual stresses by means of a multiplicative composition of the deformation gradient. As a three-dimensional finite element example, we study the material degradation of a fibre-reinforced tube subjected to internal pressure. This highlights the mesh-objective and constitutive properties of the model and illustratively underlines the capabilities of the formulation with regard to biomechanical application such as the simulation of arteries.
Tobias Waffenschmidt, César Polindara, Andreas Menzel
A Mechanically Stimulated Fracture Healing Model Using a Finite Element Framework
Abstract
In this work a biochemical fracture healing model coupled with mechanical stimulation of stem cell differentiation is investigated. A finite element scheme is applied to the underlaying advection-diffusion-reaction problem, using the Time Discontinuous Galerkin and Finite Calculus method to ensure stability of the calculation. Strains within the callus region are computed and used for a characterization of the local mechanical demand and the resulting stimulation of the healing process. A theoretical axisymmetric model of a sheep osteotomy is implemented and results of the presented FEM approach are discussed. The repair progress will be determined by the interfragmentary movement (IFM) and the mean tissue densities.
Alexander Sapotnick, Udo Nackenhorst
The Customized Artificial Hip Cup: Design and Manufacturing of an Innovative Prosthesis
Abstract
The demand for customized products has increased in recent years and will become even more important in the future. This trend is mainly observed for the medical technology sector influenced by the increasing manufacturing of patient-individual prostheses. In particular the manufacturing of customized hip cups is gaining in importance. Over 800,000 total hip replacements are performed worldwide each year. Despite this experience, the migration and loosening of the hip prosthesis especially of the cup due to the bone resorption caused by stress shielding is a current problem. Patient-specific hip cups can be used to counteract this. However, individual hip cups are only implanted for the treatment of great deformations or tumours because of the cost-intensive manufacturing. Within this project the remodelling process is calculated with a conventional prosthesis via finite element method (FEM) coupled with multi-body simulation (MBS). A migration of the cup in the proximal direction can be suggested. Based on these results an innovative and economic concept for the design and production of patient-individual hip cups for primary surgery by means of sheet metal forming is developed. In this two-stage process first standardized titanium sheet metal components are produced. Then a true-size enlargement of these components is executed by a modified adaptive rubber-die forming process. The development is accompanied by an FE simulation-based planning as well as a metal forming adapted design method. In this study the first part of the design method is demonstrated, which contains the deduction of a universal acetabular geometry, necessary for the production of the standardized component. Furthermore, high pressure sheet metal forming (HPF) will be introduced for the manufacturing of standardized components. Therefore an FE-simulation of the process is carried out for the design of the forming tool.
Stefanie Betancur Escobar, Anas Bouguecha, Amer Almohallami, Henning Niemeier, Karin Lucas, Christina Stukenborg-Colsman, Ingo Nolte, Patrick Wefstaedt, Bernd-Arno Behrens
On the Role of Phase Change in Modelling Drug-Eluting Stents
Abstract
A model of drug release from an eluting stent to the arterial wall is presented. The coating layer is described as a porous reservoir where the drug is initially loaded in a polymer-encapsulated solid phase, and is then released both to the coating and to the tissue of the arterial wall in a free phase. The wall is treated as a heterogeneous porous medium and the drug transfer through it is modeled by a non-homogeneous set of coupled partial differential equations that describe a convection-diffusion-reaction process. Change of phases due to drug dissolution in the coating and binding-unbinding reactions in the arterial wall are addressed. Numerical results show a strong coupling of the release kinetics in the polymer and the drug dynamics in the wall, and this coupling depends on the physico-chemical drug properties, the microstructure of the polymeric stent coating and the properties of the arterial wall.
Franz Bozsak, Jean-Marc Chomaz, Abdul I. Barakat, Giuseppe Pontrelli
Development of Magnesium Alloy Scaffolds to Support Biological Myocardial Grafts: A Finite Element Investigation
Abstract
Lesioned myocardial tissue can be replaced with innovative biological grafts. However, the strength of most biological grafts is initially not sufficient for left ventricular applications. Implants that mechanically support these grafts and gradually lose their function as the graft develops its strength are a possible solution. We are developing magnesium alloy scaffolds for this purpose. The finite element method was used to perform simulations wherein scaffolds are deformed according to the heart movement. This allows us to identify highly stressed regions within the implant that need design changes. Preformed scaffolds were determined to have significantly lower stresses in comparison to flat ones. The method of tensile triangles suggests shape changes for notable stress reduction. Furthermore, new scaffold shapes were developed and simulated. Two of them are recommended for further examinations through in vitro and in vivo tests. A completely new alternative scaffold concept is also proposed.
Martin Weidling, Silke Besdo, Tobias Schilling, Michael Bauer, Thomas Hassel, Friedrich-Wilhelm Bach, Hans Jürgen Maier, Jacques Lamon, Axel Haverich, Peter Wriggers
Finite Element Analysis of Transcatheter Aortic Valve Implantation in the Presence of Aortic Leaflet Calcifications
Abstract
Transcatheter Aortic Valve (TAV) implantation is a recent interventional procedure for the replacement of the aortic valve in patients affected by severe aortic stenosis who are considered at high or prohibitive surgical risk. Despite recent improvements, TAV-related complications still limit its application. In the present work, FE analyses of TAV implantation and function have been performed with the aim of investigating the influence of the calcifications of the aortic valve leaflets on TAV performances. Results suggest that the degree and location of calcifications could influence post-implanted TAV configuration as well as TAV-aortic root interactions and TAV dynamics. The study gives insights in the biomechanics of TAV, while the implemented computational tools could be applied to different scenarios to investigate other relevant clinical aspects.
Annalisa Dimasi, Marco Stevanella, Emiliano Votta, Francesco Sturla, Gaetano Burriesci, Alberto Redaelli
Repair of Mitral Valve Prolapse Through ePTFE Neochordae: A Finite Element Approach From CMR
Abstract
Patient-specific finite element (FE) modeling is largely used to quantify mitral valve (MV) biomechanics associated to pathological and post-surgical conditions. We used this approach, integrated with non-invasive cardiac magnetic resonance (CMR) imaging data, to numerically perform the repair of the isolated mitral valve leaflet prolapse through expanded-polytetrafluoroethylene (ePTFE) sutures and quantitatively compare the effects of different techniques of neochordal implantation (NCI). CMR-derived FE models well reproduced MVP-related alterations and were able to assess the efficacy of each repairing technique and its biomechanical effects on MV apparatus; the quantification of biomechanical differences between NCI techniques, especially in terms of both chordal tensions and leaflet stresses redistribution, may impact on the short- and long-term the clinical outcome, potentially opening the way to patient-specific optimization of NCIs and, if extensively and successfully tested, improve surgical planning.
Francesco Sturla, Francesco Onorati, Emiliano Votta, Marco Stevanella, Aldo D. Milano, Konstantinos Pechlivanidis, Giovanni Puppini, Alberto Redaelli, Giuseppe Faggian
An Extended Computational Framework to Study Arterial Vasomotion and Its Links to Vascular Disease
Abstract
A mathematical model of vasomotion is presented in the context of an extended computational framework, to bring new insights into the mechanisms involved in the regulation of vascular tone and arterial function. The approach is based on a number of previously published results, and provides a starting point to a unified method to modelling the pathways to endothelial dysfunction. Results are presented for different scenarios, involving a population of coupled smooth muscle cells on an image-based computational domain.
Etienne Boileau, Dimitris Parthimos, Perumal Nithiarasu
Development of a Model of the Electrically Stimulated Cochlea
Abstract
Cochlear Implants (CIs) are implantable medical devices that can restore the sense of hearing in people with profound sensorineural hearing loss. Clinical trials assessing speech intelligibility in CI users have found large inter subject variability. One possibility to explain the variability are the individual differences in the interface created between electrodes and the auditory nerve. For example, the exact position of the electrodes in each cochlea may differ from one patient to another. Additionally the amount of functional auditory neurons might also vary considerably between CI users. In order to understand the variability, models of the voltage distribution of the electrically stimulated cochlea may be useful. With this purpose we have developed a model that allows to simulate the voltage distribution at different positions on the auditory nerve. Simulations show differences in the extracellular voltage of the spiral ganglions depending on the electrode positions and the cochlear size, which might explain some of the variability. Finally, the model of the electrically stimulated cochlea has been used to simulate the extracellular voltage patterns produced by different instrumental sounds. These patterns have been inserted in an automatic instrument classifier that helps to illustrate the mentioned variability.
Waldo Nogueira, Waldemar Würfel, Richard T. Penninger, Andreas Büchner
Implant Related Infections
Abstract
The formation of biofilms on implants by bacteria is difficult to treat, life-threatening, and costly. Hence, alternatives for the prevention of biofilm infections are urgently needed. The assessment of rhythm management devices revealed colonization of 47 % by asymptomatic biofilm communities. Comparison with infected implants showed a much higher biodiversity of the infectious biofilm communities which were dominated by pathogenic Staphylococcus species. The results suggest that it is not essential to suppress any biofilm formation but only pathogenic bacteria species. The situation differed considerably for biofilms on dental implants. Here parts of the implant are always in a non-sterile environment and on all implants biofilm communities could be found. More than 60 different species could be identified from infected dental implants but contrary to the pacemakers no clear pathogen was found. The results indicate different mechanisms of infections requiring individual concepts for biofilm prevention on implants.
Wolf-Rainer Abraham
Animal Test Models for Implant-Associated Inflammation and Infections
Abstract
To evaluate the biocompatibility and inflammatory potential of prospective implant materials a mouse model was established using in vivo imaging to monitor inflammatory responses to individual implants over time. Various inflammation associated products and processes were assayed such as reactive oxygen radicals, proteases produced by immune cells, cell stimulatory signaling molecules and interferon gene activation. These were detected either by biochemical activation of fluorescent molecules or by transgenic animals expressing luciferase to monitor inflammatory interferon-\(\upbeta \) (IFN-\(\upbeta )\) induction. The results showed that inflammatory signals can be detected by in vivo imaging after subcutaneous implantation of biocompatible or immune stimulatory implants. However, there were specific differences depending upon the assay system. The response to inflammatory proteases and cell growth signaling molecules appeared delocalized and was difficult to assign to one of several implants in individual animals. On the other hand, the interferon response was locally focused and was highly specific for pathogens whereas no signal was detected in response to wounding or to biocompatible implant materials. In conclusion, of the various detection systems investigated, the transgenic interferon mouse model could be applied to monitor bacterial implant infections and will be useful to evaluate the efficacy of antimicrobial implant coatings.
Bushra Rais, Muhammad Imran Rahim, Stefan Lienenklaus, Siegfried Weiss, Christian Tolle, Jan-Marten Seitz, Henning Menzel, Hansjörg Hauser, Peter Paul Müller
Metadaten
Titel
Biomedical Technology
herausgegeben von
Thomas Lenarz
Peter Wriggers
Copyright-Jahr
2015
Electronic ISBN
978-3-319-10981-7
Print ISBN
978-3-319-10980-0
DOI
https://doi.org/10.1007/978-3-319-10981-7

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