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A N S Y S  Biomedical  Industry
A N S Y S  Biomedical  Industry
A N S Y S  Biomedical  Industry
A N S Y S  Biomedical  Industry
A N S Y S  Biomedical  Industry
A N S Y S  Biomedical  Industry
A N S Y S  Biomedical  Industry
A N S Y S  Biomedical  Industry
A N S Y S  Biomedical  Industry
A N S Y S  Biomedical  Industry
A N S Y S  Biomedical  Industry
A N S Y S  Biomedical  Industry
A N S Y S  Biomedical  Industry
A N S Y S  Biomedical  Industry
A N S Y S  Biomedical  Industry
A N S Y S  Biomedical  Industry
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A N S Y S Biomedical Industry

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ANSYS Magazine Supplement on Biomedical Industry

ANSYS Magazine Supplement on Biomedical Industry

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  • 1. ADVANTAGE Spotlight on Engineering Simulation in theBiomedical Industry s2 Making Life Longer and Better s10 Standing Up Right s4 Turning Up the Volume s12 Designing with Heart s6 Hip to Simulation s14 Going with the Flow s7 Walking Pain Free s15 Battle of the Bulge s8 Engineering Solutions for Infection Control SWEET SOUNDS FROM SIMULATION COCHLEAR IMPLANTS
  • 2. BIOMEDICAL: OVERVIEWSimulation DrivenProduct Development:Making Life Longerand BetterThe biomedical industry is emerging as astrategic user of engineering simulation.By Thierry Marchal and Kumar Dhanasekharan, ANSYS, Inc. Recent analyses show that leading biomedical com- products. There are a number of reasons for such simulationpanies around the world are continuously growing their to continue its entrenchment in biomedical product develop-investment into research and development (R&D), with an ment. First, the advancement in technologies such asincrease of 12.5 percent in 2006 that reached total R&D high-performance computing (HPC) is able to meet theexpenses exceeding $9 billion [1]. This is no surprise, given demands of biomedical product development, allowingthe need for advanced medical treatments and care due to a healthcare institutions, life science researchers and thelarge and growing population of aging individuals, the need industry to conduct large-scale simulation studies. Theto find minimally invasive treatments for conditions such as increasing ability to import computed tomography (CT)diabetes and heart disease, and the increasing demand for scans and magnetic resonance imaging (MRI) into simulationartificial organs. As medical product innovation continues to software — a process now becoming routine — makes itbecome more complex, there is a strong emerging need for feasible to address in vivo device design needs (such as withSimulation Driven Product Development, which has been respiratory drug delivery and endovascular devices), essen-seen and is broadly accepted in the semiconductor, tially enabling virtual prototyping. In addition, the integrationaerospace and automotive industries. of simulation techniques across multiphysics, from structural Simulation is becoming an integral part of the product analysis to flow modeling to thermal analysis, is enhancingdesign cycle in biomedical applications ranging from the virtual prototyping needs of the biomedical industry. Forprosthetics and artificial organs to endovascular techniques example, in studying aneurysms, ANSYS simulation toolsto surgical devices, medical equipment and diagnostic have been used to import CT scans into the simulation 1 2 3 Arterial wall Thrombus 6 5 4 Simulation Driven Product Development is being applied regularly in the biomedical industry. This aneurysm study was performed within an integrated environment to analyze coupled fluid flow and structural simulation. The steps are: 1) CT scan; 2) segmentation from scans to extract branches; 3) cuts are written in form of splines; 4) creation of solid geometry composed of arterial wall/thrombus and automatic creation of fluid volume from the solid geometry; 5) independent mesh for each simulation technique (flow modeling and structural modeling); and 6) coupled fluid and structural model with model setup, analysis and post-processing in a single environment.s2 ANSYS Advantage • Volume I, Issue 2, 2007 www.ansys.com
  • 3. BIOMEDICAL: OVERVIEWenvironment, allowing researchers to study a structuralanalysis of the weakened arteries along with the flow patternsin a single virtual environment, truly creating a virtual proto- 1type model with multiphysics, all in an integrated manner. Another growing area is drug delivery, particularly withmedicines that are released into the bloodstream or respi-ratory system. There is a need to better understand theprocess and how adjustments can be made to acceleratedrug delivery to the point of highest efficacy, which then willallow healthcare companies to design better devices thatadminister appropriate dosages. Similarly, orthopedic departments are paying moreattention to the virtual prototyping approach brought bycomputed-aided engineering (CAE). Bones are criticalpieces of the body, having complex, specific geometries;they are made of different materials exhibiting stronglynonlinear behavior. Until now, scientists have lacked proper,robust models that can be used to bring together, into a 2single simulation, characteristics as complex as poro-elasticity, nonlinear viscoelasticity and linear elasticity, whichare needed for an accurate description of an intervertebraldisc (ID), for example. The improved robustness of existingmodels together with the availability of reliable materialproperties now provides evidence that these numericalresults can bring new, invaluable information to doctors. As aresult, healthcare institutions now are studying how a hipprosthesis will perform related to a comfortable walk over along period of time as well as investigating — prior to plan-ning spinal surgery or even designing an ID implant —whether the remodeling procedure leading to the unificationof the pedicle screw and the vertebra is likely to progresssmoothly. [See Standing Up Right on page s10.] To illustrate recent concrete progress in addressing real-life problems and pain relief via CAE, this biomedical 3spotlight describes applications in which simulation tech-nology has made a major difference. Both fluid flows andsolid mechanics, or the combination of the two, appear insurprising applications. Some are critical to patient life orfunction, such as lung air flow and spine implant; otherssimply make life more comfortable through better earimplants and insole design. For the future, imagine the impact of simulation to drivethe development of patient-specific medicine and medicalcare. For example, tomorrow’s surgeons may be able to takeCT scans of patient physiology and use simulation toconduct virtual surgery as well as study the procedure’seffectiveness as part of the overall process. This is enabledthrough automation of simulation along with rapid designcomparisons through automated parametric studies — andit is rapidly becoming reality. The era of simulation in thebiomedical world is rising. ■ Proper design of a medical insole required to develop an accurate modeling of the foot at different stance phases during required ambulation: 1) the initial contact state; 2) theReferences mid-stance state; and 3) the toe-off state. The resulting data was used to calculate the pressure and stress induced on the plantar surface as well as inside deep tissues.[1] The R&D Scoreboard 2006, Volume 2, Department of Trade and Industry (DTI), U.K.www.ansys.com ANSYS Advantage • Volume I, Issue 2, 2007 s3
  • 4. BIOMEDICAL: COCHLEAR IMPLANTS Cochlear implant diagram: implant components (left) and insertion in the cochlea (right) Image From Hals-Nasen-Ohren-Heilkunde, Boenninghaus, Hans-Georg, Lenarz, Thomas, 2005, Kapitel 5 “Klinik des Innenohres,” p 116. Published by Springer Berlin Heidelberg, ISBN 3-540-21969. With kind permission of Springer Science and Business Media. Turning Up the Volume The use of shape memory alloys offers the promise of better functioning in cochlear implants. By Dieter Kardas, Institut für Baumechanik und Numerische Mechanik (IBNM), Leibniz Universität Hannover, Germany Wilhelm Rust, Fachhochschule Hannover, Germany Ansgar Polley, CADFEM GmbH, Burgdorf, Germany Tilman Fabian, Hannover Medical School, Germany Cochlear implants (CIs) are elec- CADFEM GmbH, the Hannover array could be achieved. The concept tronic hearing devices designed to University of Applied Sciences and was to design an SMA component restore partial hearing to those who are Arts, and the Leibniz University of whose shape matched that of the deaf or severely hearing-impaired. The Hannover has found that an improve- cochlea. Prior to the insertion process, devices consist of three external and ment might be possible using shape the component would be deformed two internal components. The external memory alloys (SMA). pseudo-plastically, and then, relying device comprises a microphone that Shape memory materials display on heating from the body itself, it picks up sounds from the environment, distinct thermo-mechanical behavior. would return to its original form during a speech processor and a transmitter. In the case of shape memory effect implantation. To pursue this idea, The internal components include two (SME), a body that has undergone implant simulations that accounted for surgically implanted devices: a receiver plastic deformation will return to the the pseudo-plastic deformation and that works with the transmitter to original shape or form that it had prior shape memory behavior were carried convert speech processor signals into to deformation by heating it above a out using ANSYS Multiphysics tools. electronic impulses and an electrode critical temperature. After being heated For these simulations, the team cre- array that uses those signals to stimu- and returning to its original form, a ated a material model for SMA and late the auditory nerves within the ear. shape memory material will not change implemented it in ANSYS Multiphysics One of the traditional limitations of back to its deformed shape if cooled. via user-interface USERMAT for three- the electrode array is the inability to This phenomenon can be observed in dimensional finite elements. The achieve optimal depth of insertion into many shape memory alloys, specific- phenomenological material model the cochlea, the auditory portion of the ally nickel-titanium (Nitinol), which has was developed using stress–strain– inner ear. A German team including a wide range of applications in the temperature data for SMA and was automotive and aerospace industries. based on a linear kinematic hardening In addition, due to its high biocompat- model. The stress–strain behavior of ibility, high resistance to corrosion and, shape memory materials, which is above all, the thermal-induced SME, highly nonlinear in nature and varies Nitinol is very useful in the field of with temperature, was incorporated into medical engineering. the simulation with the addition of In the case of the CI, the research a temperature-dependent scalar Deform Heat up Cool down team thought that by taking advantage parameter: the middle stress σm.Demonstration of one-way shape memory effect, from left of the thermally induced shape The shape memory stress–strainto right: initial shape of a component, deformed shape, memory behavior of Nitinol, greater curve differs from the standard linearshape on warming, shape on cooling after warming implantation depth for the electrode kinematic model in that the shape of s4 ANSYS Advantage • Volume I, Issue 2, 2007 www.ansys.com
  • 5. BIOMEDICAL: COCHLEAR IMPLANTSthe stress–strain hysteresis — whichone gets by periodically changing forcedirection — is ripped in a mannerthat varies with temperature. Shapememory alloys exhibit pseudo-plasticity at a low temperature rangeand pseudo-elasticity at a high temper-ature range. These temperature rangesdepend on the percentage compositionof nickel and titanium; generallyboth are equiatomic, which means thatthe rip of the curves increases with Pseudo-plasticity σm = 0 (left) and pseudo-elasticity σm > σy* (right). The middle stress (σm) rips the shape memory alloy stress–strain hysteresis as temperature increases.increasing temperature. The degree to which the curve isripped is determined by the mentionedmiddle stress, σm. If σm is set to zero,then the hysteresis experiences no rip,and pseudo-plasticity can be repre-sented. If σm is set to a higher valuethan the so-called amplitude stress σy*(half value of the distance from upperflow curve to lower flow curve), pseu-do-elasticity can be represented. Theactual value of the middle stress wasdetermined using experimental datataken at various temperatures. In orderto obtain a smooth, nondiscontinuousrepresentation of the flow curve, atanh-function was included in theequations that describe the offset/ripbehavior as a function of σm. By incorporating this offset-function σoff (tensor-function of ordertwo) into the material model, the shapememory behavior was effectivelycaptured with only two sets of materialconstants: one set for pseudo-plasticityand another for pseudo-elasticity.ANSYS Multiphysics software itselfinterpolates between these parametersets to provide the material constantsfor the actual temperature. With thistechnique, it was possible to reproduceany intermediary state betweenpseudo-plastic and pseudo-elasticstress–strain behavior. By including this shape memorybehavior, the CI development team wasable to simulate implantation of a shapememory cochlear implant (SM-CI) intothe cochlea. The results of a 65-secondsimulation of the implantation processsupported the idea that the temperatureof the human body could have enoughof a thermal effect on the array that,when implanted, it could return to theoriginal shape: that of the cochlea.These findings support the possibilityof a solution that can providedeeper implantation and, thus, betterfunctionality for the CI. ■ Time-spaced results of the implant simulation for a shape memory cochlear implant. The red color indicates that body temperature has been reached by the implant. Cochlear geometry data courtesy Hannover Medical School, Dr. Omid Majdani.www.ansys.com ANSYS Advantage • Volume I, Issue 2, 2007 s5
  • 6. BIOMEDICAL: ARTIFICIAL JOINTSHip to SimulationEvaluation of designs for a hip replacementprosthesis overcomes physical andscientific limitations.By Joel Thakker, Integrated Design and Analysis Consultants, U.K. Hip replacement surgery involves to model the force required to removereplacing the damaged or diseased the socket axially. A three-dimensionalball-and-socket joint configuration model was used to analyze rotationalwith artificial parts. During surgery, a removal of the joint, since a two-cup or hip socket — a dome-shaped dimensional case would not representshell/liner — is implanted into the the behavior fully. The ANSYSacetabulum portion of the pelvic girdle Mechanical simulation used nonlinearafter the bone has been hollowed out contact elements in the prosthetic hipusing a grater. The thigh, or femoral, socket and accounted for frictionportion of the hip replacement pros- between the cup and bone. In all X-ray of a hip showing a prosthesis, including the socket,thesis is composed of a analyses, the implant ball and stem. Image courtesy DePuy Orthopaedics, Inc.ball, which acts like a cup was modeled inbearing where it fits into titanium while the bonethe cup and is attached was treated as an aniso- is time-consuming and expensive into a stem that further tropic material. comparison. Physical testing is limitedattaches to the femur. For both analyses, as real bone materials are not highlyThe Duraloc® unce- IDAC created parametric available. Some synthetic and naturallymented acetabular hip models in order to evalu- occurring materials can be used, but The Duraloc® uncemented acetabularsocket, a replacement hip socket is made from titanium and ate different bone and their material properties do not pre-cup developed by has a porous coated shell. implant cup geometries, cisely match that of human boneDePuy Orthopaedics, material properties and materials. Numerical modeling allowsInc., in the U.K., uses an interference fit boundary conditions. The assembly DePuy to view detailed stress andto hold the socket in place in the hip conditions involved inserting the cup deflection distribution plots and loadbone. To assist DePuy in the design of into the bone to overcome inter- versus time history plots that cannotthe Duraloc product, Integrated Design ference, allowing the frictional effects be created easily from physical tests.and Analysis Consultants (IDAC) to hold the cup in place, and subse- Comparisons between the resultsused ANSYS Mechanical software to quently removing, either axially or obtained through simulation and thosedevelop parametric models that are rotationally, the cup from the bone to obtained from previous testing revealused to establish both the necessary establish disassembly loads. a close correlation.implantation and disassembly forces This form of modeling allows As a result of this study, DePuy hasfor variations of the replacement joint. DePuy to evaluate different configura- used this type of design evaluation in IDAC performed a two-dimensional tions of implant design numerically other orthopedic implant products,analysis on the cup assembly in order rather than by physical testing, which including artificial knee joints. ■ Contour plot of stresses induced by the inter- Three-dimension finite element model mesh Illustration of stress distribution in the hip ference fit between the prosthesis and the bone; of bone and prosthesis joint assembly after the prosthesis has been the areas colored in grey illustrate the region pressed into place of the bone that could be expected to yield during the assembly process.s6 ANSYS Advantage • Volume I, Issue 2, 2007 www.ansys.com
  • 7. BIOMEDICAL: BIOMECHANICSWalking Pain FreeNew insoles designed with the ANSYS mechanicalsuite relieve pain from foot disease.By Bum Seok Namgung, Dohyung Lim, Chang Soo Chon and Han Sung KimYonsei University, Seoul, Korea The human foot does more than Three geometries representing threesimply enable mobility. Feet are an primary states (initial contact, mid-stanceimportant part of the body because they and toe-off) during ambulation then werebear weight, absorb shock and stabilize created. The simulation models incorpo-body structure, but they usually get little rated two insole designs: one flat andof our attention. When foot disease one contoured to contact the entireappears and pressure and stress bottom of the foot. Each design wasexceed a given limit, pain occurs — analyzed at various values of elasticmaking a person suddenly aware of just modulus (0.3 MPa, 1.0 MPa and 1 GPa) inhow critical a function the feet provide. order to represent a variation in insoleFor people with diabetes, subject to firmness and identify which more effec-poor circulation and neuropathy, even tively redistributed von Mises stresses on During ambulation (top to bottom), the highestordinary foot problems can get worse the plantar, or bottom, surface of the foot pressure progressively shifts from the plantar region under the heel bone forward to theand lead to serious complications. during standing. metatarsal head bone. One research project designed During ambulation, ANSYS softwareto benefit such patients involves showed that high pressures first appeardeveloping insoles that will prevent pres- on the plantar surface region overlyingsure sores on the deep tissues inside the the heel bone for the initial contact state,plantar surface of the foot. A team at the progresses through the middle of the footInstitute of Medical Engineering at for the mid-stance state, and finally, forYonsei University in Korea is finding new the final toe-off state, is concentrated inways to gather information on the the vicinity of the metatarsal head bone atmechanical response of the foot to vari- the front of the foot. These results are inous insole designs. They are utilizing agreement with those obtained from afinite element analysis (FEA) software foot scan system used in experimentalfrom ANSYS, Inc. to design new patient- gait analysis.specific insoles that reduce both The results found that stresses on thepressure during ambulation and stress plantar surface are significantly lower withwithin the feet, ultimately relieving the total contact insole compared withpain. The team selected the ANSYS those of the flat insole; stresses also aremechanical suite because of its reliability dependent on the insole elastic modulus.and flexibility for handling complex and This confirms that customized design ofirregular geometries. Furthermore, its an insole for patients with foot disease Von Mises stress distributions on the plantarnonlinear, hyper-elastic models and may be necessary, and the solution surface of the foot using the flat (top) andadvanced contact conditions provide a should include biomechanical and clinical total contact insoles (bottom)realistic alternative to experimental points of view. ■approaches for gait analysis. Using the ANSYS technology, theresearchers first created a three-dimensional model using computerizedtomography (CT) images obtained fromthe right foot of a subject with hallusvalgus, commonly called a bunion.Commercial software, CANTIBio™(CANTIBio, Inc., Korea) and meshingsoftware were used to fine tune the Two insoles, one flat (left) and one shaped to contact the entire sole of the foot (right), were compared in this analysiscontours of the foot. to understand the impact of the geometry on foot pain. www.ansys.com ANSYS Advantage • Volume I, Issue 2, 2007 s7
  • 8. BIOMEDICAL: INFECTION CONTROLEngineering Solutionsfor Infection ControlSimulation assists in designing a hospital ward to reduce the airbornetransmission of diseases such as tuberculosis and influenza.By Cath Noakes and Andrew SleighUniversity of Leeds, U.K. microbiologists is based in the School the basic furniture, the ventilation of Civil Engineering, with strong links supply and extract vents. Isothermal to clinicians at the Leeds Teaching airflow was modeled on an unstruc- Hospitals and to academics and tured tetrahedral grid using a standard scientists around the world. Originally k–ε turbulence model. Supply air set up to investigate ultraviolet (UV) air velocities were defined to ensure a disinfection devices to combat TB, the room ventilation rate of 6 AC/h for all group now focuses on understanding simulations, and a pressure of –10 Pa airborne transmission routes with a was imposed on the extracts toHospital Nacional Dos de Mayo in Lima, Peru, was the strong emphasis on the hospitalsite of a TB ward ventilation system redesign. environment. This knowledge is used Hospital-acquired infection poses a to aid the development of newmajor problem in healthcare facilities infection control technologies and to optimize engineering strategies to Bed 1 Bed 2around the world. Although manyinfections are transmitted through hand- reduce the risk of disease.to-hand contact, airborne transmission The suitability of a ward ventilationalso may play an important role; this is system design was the subject of a Supply (ceiling)the primary mechanism for a number of recent study carried out using ANSYSinfections, including tuberculosis (TB) CFX computational fluid dynamics (CFD) software [3]. The two-bed ward in Extract (low, wall)and influenza. Airborne routes also havebeen implicated in the transmission of Hospital Nacional Dos de Mayo,hospital-acquired infections such as located in Lima, Peru, is one of amethicillin-resistant Staphylococcus number of similar rooms housingaureus, Acinetobacter spp and noro- patients with TB. Unusual to a hospital Extracts (high, wall)virus. Successful control of infection in this part of the world, the wards areinvolves breaking the chain of trans- mechanically ventilated. Any airbornemission. To do so, it is necessary transmission of TB within the hospital Bed 1 Bed 2to understand both the mode of trans- will be strongly influenced by themission as well as the nature of the imposed ventilation flow. As part of apathogen and its behavior in the wider project researching TB trans- Supply Supplyenvironment. mission, led by Dr. Rod Escombe of (ceiling) (ceiling) The role played by airborne Imperial College in London, U.K., thetransport of pathogens has been CFD study was carried out to examinethe driving force behind the research whether changes to the ward layout andcarried out by the Pathogen Control ventilation system could reduce the riskEngineering Group at the University of of cross-transmission between patients,Leeds in the U.K. for the past 10 years. staff and visitors in the hospital. Original room layout and ventilation system (top) and A simplified geometry represented proposed new layout (bottom) showing the location of theThe multi-disciplinary team of engi- partition between the two beds, the additional ventilationneers, mathematical modelers and the key features in the ward, including supply diffuser and the modified extract locations s8 ANSYS Advantage • Volume I, Issue 2, 2007 www.ansys.com
  • 9. BIOMEDICAL: INFECTION CONTROLsimulate the negative pressure that is diffuser and wall-mounted extract findings were of immediate benefit tomaintained in the real facility. As resulted in significant mixing of TB the architects redesigning the ward,the study focused on the risks of contamination throughout the room, who based the new ventilation systemcross-infection, it was important to demonstrating the high risk of cross- and ward layout directly on the studyinclude a model to represent the infection between patients. The simple results. ■release of infectious material from TB addition of a partition between the twopatients. To relate the CFD study to beds yielded an immediate benefit, www.efm.leeds.ac.uk/aerobiologypublished outbreak data, a scalar providing a physical barrier that limited Referencesinfectious particle production variable the transfer of infection between the [1] Noakes, C.J.; Sleigh, P.A.; Fletcher, L.A.;was defined in terms of units of infec- two areas. As a low-cost intervention, Beggs, C.B., Use of CFD Modeling intious dose, known as “quanta.” this could prove beneficial in resource- Optimising the Design of Upper-Room UVGI To represent a patient’s production poor countries, although it may not Disinfection Systems for Ventilated Rooms.of TB bacteria, a small inlet condition be suitable for naturally ventilated Indoor and Built Environment, 2006 15(1), pp. 347-356.was located close to the head of environments. Combining the partition [2] Noakes, C.J.; Fletcher, L.A.; Beggs, C.B.;each bed. Scalars, representing the with a new ventilation system layout, Sleigh, P.A.; Kerr, K.G., Development of ainfectious particles produced by each comprising ceiling supply diffusers Numerical Model to Simulate the Biologicalpatient, were introduced into the room above the foot of each bed with wall- Inactivation of Airborne Microorganisms inat a constant rate of 14 quanta/hour mounted extracts at the head of each the Presence of UV Light. Journal of Aerosol Science, 2004, Vol. 35(4), pp. 489-507.in order to represent the typical pro- bed, yielded the best results. Despite [3] Noakes, C.J.; Sleigh, P.A.; Escombe, A.R.;duction rate of a pulmonary TB patient. the ventilation rate remaining constant, Beggs, C.B., Use of CFD Analysis in The CFD study made it quick and the transfer of infectious material Modifying a TB Ward in Lima, Peru. Indooreasy to compare the impact of a between the two beds was reduced by and Built Environment, 2004, 15(1),number of proposed modifications to over 75 percent, representing a pp. 41-47.the ward. The original room layout with significantly reduced risk of cross-its single ceiling-mounted supply infection between patients. TheseStreamlines originating from patients 1 (red) and 2 (blue) show how Contaminant concentration contours, at an elevation of 1.4 ma partitioned room with modified ventilation system (bottom) more above the floor originating from patient 1. The figure on the topefficiently extracts contaminated air than the original room (top) does. has no partition, while the figure on the bottom uses a partition and ventilation systems local to each patient.www.ansys.com ANSYS Advantage • Volume I, Issue 2, 2007 s9
  • 10. BIOMEDICAL: SPINAL DISORDERSStanding Up RightANSYS Multiphysics sheds light on the wonders of thehuman spine and how to fix it.By Stavros Kourkoulis, Satraki Margarita and Chatzistergos Panagiotis, National Technical University of Athens, Greece The human spine is a wonder of The IVD simulation model comprised engineering work, one that is heavily four distinct volumes corresponding to used in daily activities. An important the disc’s regions: The nucleus was part of it, the intervertebral disc (IVD), is modeled as a nonlinear viscoelastic one of the most sophisticated suspen- material in a kidney-like cross section; sion and shock absorption systems the two cartilaginous vertebral endplates ever found. When disorders arise, back were considered linear elastic bodies; pain quickly can become a nightmare. and the annulus surrounding the nucleus The National Technical University of was simulated as dual laminated shell Athens (NTUA) in Greece conducted elements whose outer surfaces were a study using ANSYS Multiphysics viscoelastic in nature. The study software that revealed some secrets of analyzed various scenarios in order to The spine’s intervertebral disc how this precious structure works, as determine the contribution of each is exposed to a combination of section of the IVD to the viscous char- well as ways to fix it efficiently when it compression, bending and torsion stresses. malfunctions. acter of the entire structure. The numerical model revealed that Simulating the Intervertebral Disc the maximum stresses appeared in the The IVD is located between the ver- fibers of the intermediate volumes of the tebrae in the spine. In performing daily annulus, in the vicinities of the endplates. activities, it acts as a cushion and The nucleus was almost stress-free, as therefore is exposed to a combination expected due to its gel-like nature. of compression, bending and torsion The NTUA study also investigated the stresses. Each disc consists of the behavior of the IVD during daily activities; nucleus pulposus, a gel-like inner por- the results found that the reduction of tion of the disc; the annulus fibrosus, disc height related to a person’s 24-hour the outer portion made of about 20 daily cycle was in very good agreement lamellae of coarse collagen fibers; and with the respective experimental data by the two cartilaginous endplates, com- Tyrell et al (L3–L4 discs) [1]. posed of hyaline cartilage, located on either side of the nucleus and annulus. a b c The numerical model of the intervertebral disc: a) nucleus pulposus, b) annulus fibrosus and c) cartilaginous vertebral endplatess10 ANSYS Advantage • Volume I, Issue 2, 2007 www.ansys.com
  • 11. BIOMEDICAL: SPINAL DISORDERSThe von Mises stress distribution through the center of the disc horizontally (left) and at the point of minimum The distribution of the Mises equivalent stress in a typicalvertical cross-sectional area (right) vertebra for a pull-out displacement of 0.02 mmStudying the Surgical Remedy The parametric study assumed A comparison of the numerical results Spinal stabilization using pedicle that the vertebra consisted of cortical, with the experimental results foundscrews and rods (or plates) is one of the subcortical and cancelous bone as them to be in very good agreement,most common invasive treatments for suggested by measurements of bone within the tolerance of experimentalspinal disorders and injuries. In this mineral density of typical human error.procedure, the surgical team implants lumbar vertebrae. The simulations The main advantage of thescrews posteriorly into a number of estimated the force required to pro- numerical models lies in the accuratevertebrae and bolts them to a rod or duce a pull-out displacement of 0.02 simulation of both the structure and theplate. This assembly actively fixes the mm, the stress distribution onto the shape of the various portions of thevertebra in place, with respect to each bone, and the contact pressure on the biological disc or vertebra as wellother, and thus stabilizes that section of bone–screw interface. The results indi- as of the constitutive behavior ofthe spine. After such a procedure, some cated that the pull-out resistance could the different materials. In order toserious problems can still exist. Pain in be amplified significantly by ensuring further improve the accuracy of thesethe IVD adjacent to the fixed vertebrae that the screw was anchored into the numerical analyses, researchers mustcan occur due to failure of the spinal regions of stronger materials located develop studies using models ofinstrumentation, from either a fracture in near the cortical shell. Furthermore, the increasing sophistication adapted tostructural elements or a loosening of parameter found to have the strongest specific groups of people with mor-the screws. Experimental and clinical influence on the pull-out force was the phology and properties varying withstudies alone cannot provide a com- screw pitch. For pitch values varying age, sex, type of activities, degenera-plete view of the mechanical behavior from 2 to 5 mm, the pull-out force tions and other factors. ■of such complex structures. Numerical increased linearly by approximatelysimulations introduce a unique tool for 30 percent. The variation of the screw Referencesthe thorough and parametric study of depth and the thread inclination had [1] Tyrell, A; Reilly, T; Troup, J., Circadiansuch systems. limited impact on the pull-out force. Variation in Stature and the Effects of Spial Loading, Spine, 1985, 10(2), pp. 161-164. From the moment a pedicle screwis implanted into the vertebra, the bonebegins to regrow around the screw.This regrowth leads to the eventualcomplete unification of the bone andthe implant, which occurs about twoyears postoperatively. A fundamentalrequirement for the success of thisprocedure is the stability of the screw’sfit into the bone. NTUA used mech-anical simulation to investigate theinfluence of the vertebra structure andscrew specifications — such as depthof implantation, pitch and inclination The two phases of model construction: (left) the screw and surrounding bone implantedof the thread — on the value of the into the verterbra and (right) the regions of the verterbra (yellow: canceious bone; red: subcortical bone; blue: cortical shell)force required to loosen the screw fromthe spine.www.ansys.com ANSYS Advantage • Volume I, Issue 2, 2007 s11
  • 12. BIOMEDICAL: ARTIFICIAL ORGANSDesigning The PediaFlow ventricular assist device provides long-term cardiac support for infants.with HeartCFD-based design optimizationfor a miniature ventricular assistimplant can shave years off themedical device development cycle.By Jingchun Wu, LaunchPoint Technologies, Inc., California, U.S.A.and Harvey Borovetz, McGowan Institute for Regenerative MedicinePennsylvania, U.S.A. An important challenge facing the that integrates internally developed shear rate in the computational modeldesign of turbodynamic ventricular 3-D inverse blade design methods, of the PediaFlow is much larger thanassist devices (VADs) intended for parameterized geometry models, this threshold, so Newtonian blood withlong-term cardiac support is the opti- automatic mesh generators and math- a constant viscosity of 0.0035 Pa-s andmization of the flow geometry to ematical models of blood damage with a density of 1040 kg/s3 was assumedmaximize hydraulic efficiency while the commercial ANSYS CFX solver. for the simulations.minimizing the peak shear stress in the The system provides rapid optimiza- The CFD-predicted velocity vectorsblood flow. High efficiency reduces the tion for various types of centrifugal, at both the mid-span blade-to-bladerequired battery size while low shear mixed-flow and axial-flow blood region of the impeller and the vane-to-reduces the number of red blood cells pumps. The ANSYS CFX solver was vane region of the stay-vanes show athat are ruptured by the pump. A pedi- chosen because of its robustness for very smooth distribution without anyatric heart-assist pump is particularly computations with multiple frames of vortices at the nominal flow conditionchallenging. Due to its small size reference (MFR) (the coupling between for the optimized PediaFlow model. As(about 28 mm diameter by 51 mm rotating and stationary components). literature is replete with anecdotal evi-length), the design laws for adult-sized A new LaunchPoint VAD, Pedia- dence that recirculating flows lead topumps do not apply, and they cannot Flow™ is intended to deliver a flow rate attachment of platelets to biomaterialbe scaled. Therefore, the design of of 0.3 to 1.5 l/min against 100 mmHg surfaces — which in the clinical VADpediatric blood pumps must rely on pressure rise to neonates and infants setting can promote blood clot forma-modern design approaches to opti- weighing 3 to 15 kg. The PediaFlow tion — reverse flows and vortices aremize the flow path. Computational fluid was designed with a magnetically sus- undesirable. The CFD results founddynamics (CFD) has been widely used pended, mixed-flow style impeller with that a smooth and gradual transition inin the field of artificial heart pumps for a single annular flow gap between the the secondary flow velocity wasthe analysis of internal flow because it rotor and housing to avoid unfavorable present at the curvature of one inflowoffers an inexpensive and rapid means retrograde flow and separation. The and outflow cannula geometry. Thisof acquiring detailed flow field informa- shear stress transport (SST) model, a graduation helps to prevent separationtion that is expensive and painstaking low Reynolds number turbulence and reversal flow for the primary flowthrough in vitro testing. LaunchPoint model, was selected for the turbulent velocity. In addition, the predictedTechnologies, Inc., in the United flow simulation, which was justified pathlines of representative particlesStates, which developed the first mag- by the representative Reynolds through the entire flow region did notnetically levitated (maglev) heart pump number of ~30,000 based on the exhibit any vortices.(the Streamliner ventricular assist impeller outlet diameter and the pump The exposure of blood elements todevice that reached animal trials in tip speed. Although blood exhibits shear stress above a certain threshold1998), finds that CFD is a powerful tool non-Newtonian behavior at very low as a function of exposure time canin the performance assessment and shear rates, many studies have shown cause hemolysis, which actively breaksoptimization of artificial heart pumps. that blood can be modeled as a open the red blood cells; activate LaunchPoint has developed a CFD- Newtonian flow at a shear rate larger platelets, which can cause clottingbased design optimization approach than the threshold of a 100 s -1. The problems; and denature proteins, whichs12 ANSYS Advantage • Volume I, Issue 2, 2007 www.ansys.com
  • 13. BIOMEDICAL: ARTIFICIAL ORGANSalters the proteins so they can no longer carryout their cellular functions. Thus, it is desirableto minimize the shear stress that bloodpassing through the pump may experience.Using the results of the CFD simulation, a plotof shear stress versus exposure time forparticles passing through the pump demon-strates relative uniformity within the annularflow gap region, but it is less uniform withinboth the impeller and stay-vane regions.The overall mean blood damage through Predicted smooth velocity vectors at mid-span blade-to-blade region of the impeller (left) andthe entire domain of the model is divided mid-span vane-to-vane region of stay-vanes (right)according to the three main regions of theflow path: impeller, annular gap and the stay-vane. The analysis reveals that the hemolysislevel in the annular gap region is highest,accounting for more than 50 percent of thetotal, while the level of hemolysis in theimpeller region and stay-vane region is almostthe same, each causing approximately 20 to25 percent of the total blood damage. CFD-based design optimization with theintegration of the ANSYS CFX solver can Secondary flow streamlines at sections of inflow cannula (left) and sections of outflowsignificantly reduce the design optimization cannula (right)cycle from years, compared to the traditionaltrial-and-error methods, to just severalmonths. It provides detailed and useful flowfield information from which blood damagemay be computed, and it also predicts thehydrodynamic characteristics such as therelationship of developed pressure andefficiency to flow rate. ■This research was supported in part by NIH ContractNo. HHSN268200448192C (N01-HV-48192). Pathlines of particles at inflow cannula and impeller side (left) and stay-vanes side and outflow cannula (right)PediaFlow is a trademark of WorldHeart, Inc. 300 0.0025 0.002337 0.002341 Giersiepen 250 0.0020 Heuser Shear Stress (Pa) 200 0.0015 57.7% dHb 52.5% 150 0.0010 100 26.27% 22.8% 21.20% 19.5% 0.0005 50 0 0.0000 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 Impeller Annular Gap Stay Vane Total Shear stress history from impeller inlet to stay-vane outlet Proportion of total blood damage at different pump components under nominal flow conditionwww.ansys.com ANSYS Advantage • Volume I, Issue 2, 2007 s13
  • 14. BIOMEDICAL: IMAGING Going with the Flow Functional biomedical imaging through CFD provides By Jan De Backer and Wim Vos FluidDA nv, Antwerp, Belgium a new way of looking at pathological lungs. Reconstructed airway of a patient with cystic fibrosis: Contour plots show the effect that the use of a bronchodilator has on the local values for airway (left) volume and The red arrows indicate regions in which inflammation resistance (right); red indicates high values and blue indicates low values. has restricted the airways. Diseases such as asthma, chronic using CFD. The fluid and structural simulate and examine the air flow. Flowobstructive pulmonary disease (COPD) dynamics company combines clinical patterns, relative pressure drops andand cystic fibrosis can have a signifi- experience and capabilities with drug delivery profiles are readilycant adverse impact on the structure numerical simulations to offer a variety extracted from the simulation results.and integrity of the lungs’ airways. of services to the healthcare industry. The resistance distribution — definedWhile functional magnetic resonance The workflow process begins with as the total pressure drop over variousimaging (MRI) allows for measure- the conversion of CT scan data into a lung segments — also is available.ment of air flow, computational fluid 3-D computer model of the airway, The pharmaceutical and medicaldynamics (CFD) provides highly performed with the Materialise product device sectors also can benefit fromdetailed information of local flow Mimics. FluidDA then uses TGrid patient-specific flow analysis as a waycharacteristics and resistances. The software to create surface and volume to evaluate performance and efficacy infirst requirement of a patient- meshes and FLUENT technology to a virtual patient population. In clinicalspecific analysis is knowledge studies, it is possible to analyze For patients with deformation of the spinal column (kyphoscoliosis),of the bounding walls of the simulation can be used to determine the site of obstruction and/or the effect of bronchodilatingpatient’s flow domain — their lung respiratory function. medication, which widens lung airgeometry. This type of information passages and relaxes bronchialusually comes from computed Stent location smooth muscle to ease breathing,tomography (CT), a scan that indi- on airway volume and flow resist-cates detailed information about ance. A researcher then can beginlung geometry because of the to establish correlations betweennatural contrast between air and drug deposition patterns and clini-the lung walls. The main draw- cal outcomes, thereby providingback of CT is that the resulting an indication as to why the drugscan is a static image. Coupling Obstruction site (and subsequent location) of an intrabronchial stent, does or does not work. Functionalcomputational analyses of air flow which re-inflated the blocked lower right lung lobe. Pressure contours imaging also can be used to are plotted in the airway.with the lung scan has the poten- assess the placement of intra-tial to provide significant added bronchial devices such as stentsvalue to the clinical evaluation of and valves.lung function. Coupled with CFD, such FluidDA, a spin-off of the imaging can dramatically increaseAntwerp and Ghent universities in insight into medical assessmentBelgium, has successfully devel- and improve the accuracy of Lower lobeoped a workflow for predicting air medical interventions. ■flow in healthy and diseased lungs An increase in the volume of the lower lobe is clear in time following insertion of a stent. s14 ANSYS Advantage • Volume I, Issue 2, 2007 www.ansys.com
  • 15. BIOMEDICAL: SURGICAL TOOLSBattle of the BulgeRapid prototyping results in a new surgical toolto treat back pain.By Joe Richard, HydroCision, Massachusetts, U.S.A.Brenda Melius, consulting firm, New Hampshire, U.S.A. In the United States, back pain is one of the most com-mon reasons for healthcare visits and missed work. Fourout of five adults have at least one bout of back pain atsome point in their lives. A common source of pain is from a bulging interverte-bral disc impinging on spinal nerves, which can cause backpain or sciatica (pain down the leg) — a condition knownas herniated disc. The intervertebral disc is sandwichedbetween the vertebrae of the back and acts as a shockabsorber during spinal movement. The disc is made of twoparts: a tough outer wall called the annulus and a gelatinousinner core called the nucleus. Trauma or aging of the disccan cause the annulus to bulge. Most occurrences of lower back pain resolve with restand medication. For many people, though, the pain can be The SpineJet repairs a herniated intervertebral disc by removing a portion of thedebilitating and last for several months to years. Such nucleus. The tool uses the Venturi effect created by high-velocity saline jets topatients typically require surgery. cut and then aspirate targeted tissue. Image courtesy T.G. Communications Minimally invasive surgical techniques offer many bene-fits, since traditional back surgery can cause further pain As physicians adopt new technologies, their productand complications. HydroCision, which develops and man- demands increase. HydroCision saw CFD as a technologyufactures fluidjet-based surgical tools in the United States, that could reduce development time and improve productused computational fluid dynamics (CFD) to improve a performance. Manufacturing limitations with the existingnovel minimally invasive surgical treatment called SpineJet nozzle affected the flow divergence, directionalityHydroDiscectomy™. and alignment with the evacuation tube. By redesigning the The goal of HydroDiscectomy is to decompress the SpineJet nozzle for better flow characteristics and greaterherniated disc. When performing the procedure, a physi- ease of manufacture, the surgical device could be madecian uses a tool called the SpineJet® to remove a portion of more consistent and cost-effective. HydroCision’s productnucleus, which debulks the disc and retracts the bulge. development team used FLUENT software in analyzing theThe device uses a high-pressure jet of sterile water performance of the existing nozzle geometry. CFD simula-directed into an evacuation tube. The jet is attuned to cut tions allowed new geometries to be designed and analyzedthe softer nucleus but protect harder surrounding tissues for performance in a matter of hours to days. Optimizationsuch as the vertebrae and the annulus. The water jet natu- of the device was faster and less expensive than the tradi-rally provides cutting and a low-pressure Venturi to draw tional method of making and testing prototypes.the nucleus to the jet, cut it and aspirate it through an The CFD model included flow simulations through theevacuation tube. supply tube, nozzle orifice and evacuation region. CFD results helped the HydroCision team visualize critical flow characteristics such as the velocity profile, pressure distri- bution and flow divergence (cone angle). The team modeled six alternate SpineJet designs that incorporated significant changes to the nozzle and/or the supply tube. Engineers selected velocity magnitude and general jet shape as the primary means for comparing the different designs, since these two parameters are con- sidered the most accurate predictors of overall SpineJet Supply and evacuation tube of the original SpineJet performance. Image courtesy T.G. Communications.www.ansys.com ANSYS Advantage • Volume I, Issue 2, 2007 s15
  • 16. BIOMEDICAL: SURGICAL TOOLS CFD results for the existing SpineJet showed the influ-ence of a sharp-edge orifice and its location on the flowcharacteristic. As expected, the orifice creates a flow sepa-ration at the corner, and a vena contracta is formed. Inaddition, the proximity of the orifice to the 90-degree-bend inthe supply tube and the additional supply tube length pastthe orifice create a non-uniform flow condition at theorifice entrance. As a result, the region of highest flowvelocity is concentrated in the lower portion of the orifice;therefore, the flow is neither symmetrical nor well developed. CFD results for the alternate SpineJet designs showedsubstantial improvement compared to the existing design.Three of the alternate configurations had 20 percent highermass flow rates than the existing design as well as a 40percent reduction in cone angle (flow divergence). Thesedesigns had general jet shapes that were symmetrical andwell developed. They also retained higher flow velocitiesover longer distances from the orifice exit. Historically, HydroCision manufactured prototypes ofnew geometries for testing to examine the feasibility ofproducing a new and improved design. Although fairlyeffective, this method was costly (more than $15,000 for Cross-sectional view of all fluid volumes for original SpineJet design (top) with close-up section indicated by the red box at orifice (bottom).each design tested) and time-consuming (taking approxi-mately six months). Furthermore, testing did not alwayslead to a full understanding of the fluid flow characteristicsthat occur. Computer modeling utilizing FLUENT software pro-vides a different approach to the problem. The onlyexpenses are computing and software costs; creating aCFD model and running it takes just a few days. This allowsHydroCision to model and refine many designs in a fractionof the time it would take to manufacture and test a singleprototype. In addition, computer simulation can yield betterinsights into the interactions between the geometry and the Cross-sectional view of SpineJet alternative design colored byfluid flow. Finally, the graphics generated by FLUENT soft- velocity magnitudeware help stakeholders better understand the operation ofthe surgical tool. ■Cross-sectional view of all fluid volumes About the Industry Spotlight Cover image: Simulation demonstrates shape memory for a cochlear implant. Supply tube volume Photo courtesy Cochlear GmbH. Simulation courtesy Fachhocshule Hannover – Supply tube 90° University of Applied Sciences and Arts, CADFEM GmbH and Dr. Omid Majdani bend volume – Hannover Medical School. For ANSYS, Inc. sales information, call 1.866.267.9724, or visit www.ansys.com. To subscribe to ANSYS Advantage, go to www.ansys.com/subscribe. ANSYS Advantage is published for ANSYS, Inc. customers, partners and others Supply tube interested in the field of design and analysis applications. Neither ANSYS, Inc. nor the editorial director nor Miller Creative Group guarantees or warrants volume accuracy or completeness of the material contained in this publication. ANSYS, ANSYS Workbench, CFX, AUTODYN, FLUENT, DesignModeler, ANSYS Mechanical, DesignSpace, ANSYS Structural, TGrid, GAMBIT, and any and all ANSYS, Inc. brand, product, service and feature names, logos and slogans are registered trademarks or trademarks of ANSYS, Inc. or its subisdiaries located in the United States or other countries. ICEM CFD is a trademark licensed by ANSYS, Inc. All other brand, product, service and feature names or trademarks Orifice volume Evacuation tube volume are the property of their respective owners.s16 ANSYS Advantage • Volume I, Issue 2, 2007 © 2007 ANSYS, Inc. All rights reserved. www.ansys.com

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