Biomedical Engineering Minicourse

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Biomedical Engineering Minicourse

Multiphysics

COMSOL

V ERSION

3.5

How to contact COMSOL: Benelux COMSOL BV Rntgenlaan 19 2719 DX Zoetermeer The Netherlands Phone: +31 (0) 79 363 4230 Fax: +31 (0) 79 361 4212 info@comsol.nl www.comsol.nl Denmark COMSOL A/S Diplomvej 376 2800 Kgs. Lyngby Phone: +45 88 70 82 00 Fax: +45 88 70 80 90 info@comsol.dk www.comsol.dk Finland COMSOL OY Arabianranta 6 FIN-00560 Helsinki Phone: +358 9 2510 400 Fax: +358 9 2510 4010 info@comsol.fi www.comsol.fi France COMSOL France WTC, 5 pl. Robert Schuman F-38000 Grenoble Phone: +33 (0)4 76 46 49 01 Fax: +33 (0)4 76 46 07 42 info@comsol.fr www.comsol.fr

Germany COMSOL Multiphysics GmbH Berliner Str. 4 D-37073 Gttingen Phone: +49-551-99721-0 Fax: +49-551-99721-29 info@comsol.de www.comsol.de Italy COMSOL S.r.l. Via Vittorio Emanuele II, 22 25122 Brescia Phone: +39-030-3793800 Fax: +39-030-3793899 info.it@comsol.com www.it.comsol.com Norway COMSOL AS Sndre gate 7 NO-7485 Trondheim Phone: +47 73 84 24 00 Fax: +47 73 84 24 01 info@comsol.no www.comsol.no Sweden COMSOL AB Tegnrgatan 23 SE-111 40 Stockholm Phone: +46 8 412 95 00 Fax: +46 8 412 95 10 info@comsol.se www.comsol.se Switzerland FEMLAB GmbH Technoparkstrasse 1 CH-8005 Zrich Phone: +41 (0)44 445 2140 Fax: +41 (0)44 445 2141 info@femlab.ch www.femlab.ch

United Kingdom COMSOL Ltd. UH Innovation Centre College Lane Hatfield Hertfordshire AL10 9AB Phone:+44-(0)-1707 636020 Fax: +44-(0)-1707 284746 info.uk@comsol.com www.uk.comsol.com United States COMSOL, Inc. 1 New England Executive Park Suite 350 Burlington, MA 01803 Phone: +1-781-273-3322 Fax: +1-781-273-6603 COMSOL, Inc. 10850 Wilshire Boulevard Suite 800 Los Angeles, CA 90024 Phone: +1-310-441-4800 Fax: +1-310-441-0868 COMSOL, Inc. 744 Cowper Street Palo Alto, CA 94301 Phone: +1-650-324-9935 Fax: +1-650-324-9936 info@comsol.com www.comsol.com For a complete list of international representatives, visit www.comsol.com/contact Company home page www.comsol.com COMSOL user forums www.comsol.com/support/forums

Biomedical Engineering Minicourse COPYRIGHT 19942008 by COMSOL AB. All rights reserved Patent pendingThe software described in this document is furnished under a license agreement. The software may be used or copied only under the terms of the license agreement. No part of this manual may be photocopied or reproduced in any form without prior written consent from COMSOL AB. COMSOL, COMSOL Multiphysics, COMSOL Script, COMSOL Reaction Engineering Lab, and FEMLAB are registered trademarks of COMSOL AB. Other product or brand names are trademarks or registered trademarks of their respective holders.

Version:

September 2008

COMSOL 3.5

C O N T E N T SIntroduction Hip Replacement Introduction . . . . . . . . . . . . . . . . . . . . . . . . Model Definition . . . . . . . . . . . . . . . . . . . . . . . Results. . . . . . . . . . . . . . . . . . . . . . . . . . . Modeling Using the Graphical User Interface . . . . . . . . . . . . Drug Release from a Biomaterial Introduction . . . . . . . . . . . . . . . . . . . . . . . . Model Definition . . . . . . . . . . . . . . . . . . . . . . . 2 3 3 3 4 5 9 9 9

Results and Discussion. . . . . . . . . . . . . . . . . . . . . 13 Reference . . . . . . . . . . . . . . . . . . . . . . . . . 15 Modeling Using COMSOL Reaction Engineering Lab . . . . . . . . . 16 Modeling Using COMSOL Multiphysics . . . . . . . . . . . . . . 22 Tumor Removal Introduction 26

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Model Definition . . . . . . . . . . . . . . . . . . . . . . . 27 Results and Discussion. . . . . . . . . . . . . . . . . . . . . 28 Reference . . . . . . . . . . . . . . . . . . . . . . . . . 30 Modeling Using the Graphical User Interface . . . . . . . . . . . . 30 Creating the Geometry from Scratch . . . . . . . . . . . . . . . 36 Biomedical Stent Introduction 41

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Model Definition . . . . . . . . . . . . . . . . . . . . . . . 42 Results. . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Modeling Using the Graphical User Interface . . . . . . . . . . . . 46

CONTENTS

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Biomedical Engineering Minicourse

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I n t r o d uc t i onJoin this class to get insight how to set up biomedical models such as tissue heating and drug targeting. The training exercises are from many different engineering areas and you will use a multitude of different products and application modes of COMSOL Multiphysics. The following examples will be discussed and built during the short-course: Structural analysis of a hip joint replacement prosthesis Drug Release from a Biomaterial Tumor removal by electrode treatment Treatment of atherosclerosis with stenting Enjoy your modeling!

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BIOMEDICAL ENGINEERING MINICOURSE

Hip ReplacementThis example gives an overview of basic modeling: It shows how to import a 3D geometry from a COMSOL native geometry format, how to create the mesh, set boundary conditions and material properties, and how to solve the model.

IntroductionThe most common reason that people have hip-replacement surgery is the wearing down of the hip joint that results from osteoarthritis. Other conditions, such as rheumatoid arthritis (a chronic inflammatory disease that causes joint pain, stiffness, and swelling), avascular necrosis (loss of bone caused by insufficient blood supply), injury, and bone tumors can also lead to the breakdown of the hip joint and the need for a hip replacement.

Model DefinitionThis exercise is inspired by work of Professor Richard Hart, Ohio State University.GEOMETRY

The hip joint is called a ball-and-socket joint because the spherical head of the thighbone (femur) moves inside a cup-shaped hollow socket (acetabulum) in the pelvis. To duplicate this action, a complete hip-replacement implant has three parts: the stem, which fits into the femur and provides stability; the ball, which replaces the spherical head of the femur; and the cup, which replaces the worn-out hip socket (not shown in the nearby figure).

Figure 1: Geometry of the hip replacement.

HIP REPLACEMENT

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PHYSICS

This example models the replacement hip using the Solid, Stress-Strain application mode.MATERIAL PROPER TIES AND SUBDOMAIN SETTINGS

A metal with FDA approval for orthopedic implants is an alloy made of cobalt, chromium, and molybdenum. A reasonable value for the Youngs modulus is 220 GPa, and 0.33 for Poissons ratio. The Youngs modulus for the thighbone is set to 2 GPa.BOUNDARY CONDITIONS

Although in reality the femoral hip component would be well supported by the surrounding bone, this example applies boundary conditions that idealize a drastically lowered stiffness of the surrounding bone (which would require revision surgery). Specifically, this example uses boundary-load expressions that approximate the stiffness of the supporting thighbone with the bones stiffness drastically lowered (to 10% of the original value) at some height (0.05 m from the bottom of the stem). It then applies a normal load to the femoral heads top surface. The load is assumed to vary linearly from zero at the horizontal edge of the top surface to its maximal value at the top of the head. This maximal value, in turn, is adjusted to result in a specified value of the total downward force on the hip. In extreme cases (such as when climbing stairs), the force on the hip can be 3.5 times body weight. Assume that the body weight is 100 kg.

ResultsFigure 2 illustrates the von Mises stresses and the deformed shape. The figure reveals moderate stress levels in the stem.

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BIOMEDICAL ENGINEERING MINICOURSE

The yield stress levels are approximately in the range 430 MPa to 1028 MPa for cobalt-based alloys, and the von Mises stress levels are thus well below these levels in Figure 2.

Figure 2: The deformed shape and the von Mises stress in the hip replacement.

Modeling Using the Graphical User InterfaceMODEL NAVIGATOR

1 In the Model Navigator go to the New page and select 3D from the Space dimension

list.2 In the list of application modes select Structural Mechanics Module>Solid, Stress-Strain>Static analysis. 3 Click OK to close the Model Navigator.GEOMETRY MODELING

Importing the Geometry from a Binary File1 From the File menu, select Import>CAD Data From File.

HIP REPLACEMENT

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2 In the Import CAD Data From File dialog box, make sure that either COMSOL Multiphysics file or All 3D CAD files is selected in the Files of type list. 3 Locate the file hip_replacement_geometry.mphbin, then click Import.OPTIONS AND SETTINGS

1 Select Options>Constants, then click the Import Variables From File icon. Browse

through the course CD and import the file hip_replacement_constants.txt.

Note that the Youngs modulus defined in the constants file is that for the thighbone; you enter the properties of the alloy material manually.2 Click OK. 3 Select Options>Expressions>Scalar Expressions, then click the Import Variables From File icon. Browse through the course CD and import the filehip_replacement_expressions.txt.

These expressions define the boundary loads representing the thighbone in accordance with the assumptions discussed in the Boundary Conditions section.4 from the Options menu, select Expressions>Boundary Expressions.

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BIOMEDICAL ENGINEERING MINICOURSE

5 Select Boundaries 13, 14, 38, and 39 by pressing the Ctrl key while clicking on the

boundary numbers in the Boundary selection list.6 In the Name edit field type Fn, and in the Expression edit field type1.5*sy_mean*(y-0.14[m])/0.02[m].