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Measurements and Input for Biomechanical SimulationBrian Walker
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Bridging the gap
This meeting will include speakers from the areas of biology, biosciences and biomechanics
and will explore and demonstrate new developments and tools which are now available for
solving many problems which link these disciplines. Here for instance, mechanotransduction,
tissue engineering and nano/micro/macro models of biological structures are some of the
new areas where collaboration between the biosciences, engineering and computer
technologies are proving to be particularly fruitful. It is the aim of this meeting to focus on
‘bridging the gap’ between biologists and bioengineers by providing examples of applications
and explanations of how the various scientific tools now being developed, can be
successfully applied in practice.
Biologists Bioengineers
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Where are we now?
Engineers
Biologists
Clinicians
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Outline
� Advanced mechanical computer simulation
� Examples in bio-engineering
� Modelling the shaken baby syndrome
� Eye model -
� Data from Imaging software
� Head and neck model –
� Data from Imaging software
� Sharp force study –
� Material investigation of a biosimulant
� Auxetic foam –
� Small scale modelling
� Future and challenges in bio-engineering
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Terminology� Solution Methods� Lagrange
� Euler
� Arbitrary Lagrangian-Eulerian (ALE)
� Smooth Particle Hydronamic (SPH)
� Element Free Gerlekin (EFG)
� Computational Fluid Dynamics (CFD)
� Strains� Engineering Strain
� True Strain
� Volumetric Strain
� Plane Strain
� Green-Lagrange Strain
� Green-Saint Venant Strain
� Stresses� Von-Mises Stress
� Principal Stress
� Stress Invarients
� 1st Piola-Kirchhoff Stress Tensor
� 2nd Piola-Kirchhoff Stress Tensor
� Plane Stress
� Material Models� Elastic
� Orthotropic Elastic
� Arruda Boyce
� ViscoElastic
� Non-Linear Elastic
� Hyper Elasticity
� Plastic Kinematic� Poisson’s Ratio
� Young’s Modulus
� Yield
� Newtonian Fluid
� Non-Newtonian Fluid
� Hardening Modulus
�NOT
TODAY
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Oasys LS-DYNA Environment Software
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LS-DYNA – best known for
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LS-DYNA – best known for
Typical state of the art vehicle crash model includes:
� Sheet metal structure – steel or aluminium
� Connections eg. spotwelds, seamwelds, rivets (SPR), bolts
� Glazing
� Power train - engine, gear box, etc.
� Wheels, tyres, suspension
� Seats including frame and foam
� Occupant models (models of bio-fidelic test dummies)
� Restraint systems – airbags and seatbelts
� Sensors and accelerometers
� Crash barriers (honeycomb)
Model Size
� 2,500,000 elements
� Event time 120 – 250 ms
� Analysis time 16 hours on 16 cpus
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LS-DYNA – best known for
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LS-DYNA – best known forEarly 1990’s
25,000 elements
2007
2,500,000 elements
Image courtesy of Jaguar Cars
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LS-DYNA – Main features
• Extensive element library
• Complex contact algorithms
• Over 200 constitutive models
• Explicit and Implicit Time Integration Schemes
• Lagrange, ALE, Euler and meshless methods
• Fluid Structure Interaction
• Non-Linear Dynamics, Large Deformation
• MPP – job can run simultaneously on many processors allowing large complex problems to be solved
• Thermal analysis coupled to structural analysis
• Navier-Stokes compressible and incompressible fluid flow being added Multi Physics
Simulation
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LS-DYNA Material Models
• LS-DYNA has a library of over 200 constitutive models. Many of these are
suitable for use in biomechanical modelling. Examples include:
• Piecewise Linear Plasticity
• Plastic Kinematic
• Johnson Cook
• Various Rubber models
• Various Foam models
• Various Concrete models
• Fabric
• Honeycomb
• Composites
• ……
• Elastic
• Isotropic, Orthotropic, Anisotropic
• Mooney-Rivlin
• Viscoelastic
• Non-linear orthotropic
• General Viscoelastic (Maxwell model)
• Orthotropic Viscoelastic
• Soft tissue
• Arruda Boyce
• Heart Tissue
• Lung Tissue
• Quasilinear Viscoelastic
• Rigid
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Modelling Stages
• Geometry
� Scan
� Measure
• Boundary Conditions
� Restraints
� Constraints
� Loading
� Prescribed motion
• Constitutive Modelling
� Choose appropriate material model
� Get material constants to use
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LS-DYNA
SCAN
MESH
SET-UP
ANALYSE
POST-PROCESS
Oasys Software + Simpleware
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Scanning
LS-DYNA Model
+ScanFE
Meshing & Material Properties
+ScanCAD
CAD import &
positioning
ScanIPImageProcessing
CT, Micro-CT, MRI, Tiff, Jpg ..etc.
Simpleware
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Modelling the Shaken Baby Syndrome – Study I• Sheffield University, Department of Mechanical Engineering. I. Howard, E. Patterson and
co workers. 2001
• Physical child abuse is common
• In UK estimated that 200 infants may die from brain injuries arising from violent shaking.
• Perhaps 400 survive with severe mental & physical disability
• Damage to the retina (light sensitive part of eye)
• Is often found in shaken babies together with brain injuries
• Combined brain and eye injuries are rare in severe accidental head trauma
Ophthalmology Pictures of Retinal
Haemorrhages (shown as dark spots) in the Eyes of Shaken Babies [Habib, N E – Visual Loss from Bungee Jumping. Brit. J.
Ophthalmology, 343(8895), P487, 1994 ]
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• Study included:
• Test work - volunteers asked
� to shake nine month old baby to exhaustion (typically 20 seconds)
� to shake as violently as possible [10g <amax<20g]
� Record accelerometer data as input into LS-DYNA model
• Analytical work
� Two part model created
� Skull and brain
� Skull and eye
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• Skull [E=6500MPa u=0.2 r=1500kg/m3 t=10mm ]
• Cerebrospinal fluid [E=0.1MPa u=0.49 r=1040kg/m3 G=0.5MPa]
• Brain [E=0.675MPa u=0.49 r=1040kg/m3 G=1.68MPa]
Skull and brain model
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Four components
� Eye socket (red)
� [E=6500MPa o.d.=30mm ]
� Retina (not visible)
� [E=20kPa ρ=1050kg/m3]
� Sclera (purple)
� [E=100MPa ρ=2000kg/m3 o.d.=24mm ]
� Vitreous (blue)
� [E=10kPa ρ=1040kg/m3 o.d.=22mm p=13.2kPa]
Eye model
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Max. stress in retina during 1st cycle Brain Shear stress
Displacements of Sclera
equator (forced)
poles (free)
Initial results showed:
• Retina is susceptible to accumulative stress during shaking cycles
• Pressure in brain increases with repeated shaking
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Modelling the Shaken Baby Syndrome – Study IISheffield University, Department of Mechanical Engineering. J Rowson, D Batterbee, 2008
� To study the hypothesis “That infants are more susceptible to SBS
due to the presence of the fontanelle”
� As the brain cavity is not rigidly enclosed, damage to the brain and
surrounding tissues is more likely
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� Initial aim of present work
� To validate Fluid Structure Interaction (FSI) models using
more formal methods e.g. using various sinusoidal
excitations of different amplitude and frequency
Cerebrospinal fluid
• 320 Solid Elements
• MAT Elastic_Fluid
Brain
• 768 Solids
• MAT Elastic
Fontanelle
• 8 Shells
• MAT ElasticSkull
• 56 Shells
• Rigid
• Fluid elements have Lagrangian formulation i.e. nodes move and deform with the material
• Nodes between fluid and surrounding parts are merged i.e. contact definitions are not required
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Eye Model
Data acquisition
Segmentation
FE and STL model generation
Impact simulation in
LS-DYNA
� Patient specific computer models of the human eye based on in vivo MRI
acquisitions were constructed
� Bio-fidelic three dimensional numerical meshes of the orbital area
including the eye and surrounding soft and hard tissues generated
� Impact with projectile modelled using LS-DYNA
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• A 29 year Caucasian female
• Models constructed based on two high
resolution MRI scans of the right orbital area (using head coil and surface coil)
• In-plane and out-of-plane resolution of 1mm. The data consisted of 50 slices, each at a pixel resolution of 128x128
• Transparent top view of model showing
each mask including bone, skin, globe, fatty tissue and muscles
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• Segmentation within ScanIP
• 6 different segmented structures
� Globe and optic nerve
� Bony orbit
� Eyelids
� Fat
� Facial soft tissues
� Extra-ocular muscles
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• Volume mesh: mixed hex/tet elements or pure tet.
• Structures/parts modelled either as volumetric meshes or as surface meshes as
required (e.g. the bony orbit modelled as a rigid structure defined by surface shells)
• Model completed in Oasys PRIMER
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Head and Neck Model
26 Year old Male MRI Scan
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Head and Neck Model
• Data created by Simpleware (ScanIP and ScanFE) and Oasys PRIMER
• Research model to study different material models
• Model contains 2,000,000 solid elements
� Brain
� Skull
� Cervical Vertebrae
� Intervertebral Disks
� Mandible
� Eye
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Head Impacted Pressure Wave in Brain
Stresses in Intervertebral Disks
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Head and Neck Model II
• More detailed model – 10,000,000 elements
� Brain
� White Matter
� Gray Matter
� Stem
� Horn
� Cerebellum
� CSF
� Skull
� Cervical Vertebrae
� Intervertebral Disks
� Mandible
� Eye
� Fatty Tissue
� Optic Nerve
� Nasal Cavity and Airway
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Sharp Force Study
• Study to be able to model the effects of glass shards from a shattered window in a blast
event
• Glass Shards into gelatine –with and without skin (chamois leather)
� 1.0 m/s – 10.84 m/s
• Test on gelatine alone with non-piercing probe
• Study of glass shard into biosimulant material (gelatine)
• LS-DYNA applied to simulating the penetration of glass shards into the human body projected from exploding glazing and façades (potential terrorist bomb attacks)
• Arup Security Consulting regularly couple LS-DYNA with blast models to simulate the effects of bomb blasts on structures. This expertise will be applied to human body modelling to predict injury
potential from blast.
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Video from Tests
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• Probe can be analysed using standard Lagrange element formulation
• Sharp force, with large penetration – SPH (meshless) method being investigated
Lagrange vs SPH for probe into gelatine
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SPH for glass shard into gelatine
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SPH for glass shard into gelatine
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• Foams have a negative Poisson’s ratio – expands in all directions when stretched
• Areas of application
• Prosthetic materials
• Surgical implants
• Suture/muscle/ligament anchors
• High resolution scan of foam courtesy of Prof. Gerry Seidley, University of Washington
• Mesh generated using ScanIP and +ScanFE
• Analysed in LS-DYNA – explicit code allows a high volumetric compression to be analysed
Segmentation Mesh Set Up
Auxetic Foam
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• Auxetic Material
� Negative Poisson’s ratio
� Contracts compression / expands tension
� Example application: filters
• Synchrotron XMT
� 0.003 mm resolution
In collaboration with:
NASA Glenn Research Center
University of Washington
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Future/Challenges in Bioengineering
� Improve and further develop constitutive modelling
� Material values to use in constitutive models
� Ways to measure material values
� Complex multi-physics simulations of complete biological structures
� A framework of biocomputational techniques
� tissue engineering
� micro CFD
� mechanotransduction
� Multi level techniques, macro – micro (- nano ??)
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Contact Information
Arup
The Arup Campus
Blythe Valley Park
Solihull, West Midlands
B90 8AE, UK
T +44 (0)121 213 3399
F +44 (0)121 213 3302
www.arup.com/dyna
