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Rat brain injury mechanism identification through indentation experiment FE
reconstruction
D. BAUMGARTNER, M. LAMY, R. WILLINGER DEPARTMENT OF FLUID AND SOLID MECHANICS
STRASBOURG UNIVERSITY – FRANCE
M. GILCHRIST DEPARTMENT OF MECHANICAL ENGINEERING
UNIVERSITY COLLEGE DUBLIN – IRELAND
CONTEXT
Rat brain injury mechanism identification through indentation experiment FE reconstruction
Context: TBI
Traumatic Brain Injuries (TBI): Major cause of deaths and disabilities
235/100,000 (EU) 103/100,000 (USA)
Double cost
Mild and severe TBI : not fully explored
Motor-vehicle incidents
Falls Sport-related
Other
Rat brain injury mechanism identification through indentation experiment FE reconstruction
Context: Mechanical sollicitations
Mechanical loading results in an brain response
Criteria in head protection systems and standards
Need for injury criteria models Experimental models Numerical models Combination of both models
(Deck et al., 2008)
Rat brain injury mechanism identification through indentation experiment FE reconstruction
Context: Rat brain FE models
Shreiber et al., 1997 (University of Pennsylvania)
Gefen et al., 2003 (University of Pennsylvania)
Levchakov et al., 2006 (University of Pennsylvania)
Pena et al., 2005 (University of Cambridge)
Mao et al., 2006 (Wayne State University)
Zhu et al., 2010 (Wayne State University)
Fijalkowski et al., 2009 (Medical College of Wisconsin)
Strasbourg University Model, 2009
Rat brain injury mechanism identification through indentation experiment FE reconstruction
Context: Objectives of the study
Reconstruct real experimental protocols with our rat head FEM: Indentation loading from the University College Dublin Compare experimental findings and calculated mechanical response
Contribute to the knowledge on mild and severe TBI from a mechanical point of view
Rat brain injury mechanism identification through indentation experiment FE reconstruction
EXPERIMENTAL
PROTOCOL
Rat brain injury mechanism identification through indentation experiment FE reconstruction
Experimental setup: Device
Submission of the rat brain to an indentation at two different displacement amplitudes: 0.87 mm (low impact group) and 2.62 mm (high impact group)
The University College Dublin device
for the induction of rat brain indentation
Rat brain injury mechanism identification through indentation experiment FE reconstruction
Experimental results: Histology and MRI
Rat brain injury mechanism identification through indentation experiment FE reconstruction
a: MRI of animal from low (1) and high (2) impact group
b: Hematoxylin and eosin stain of animal from low (1) and high (2) impact group
Experimental results: Volume variations
Corpus callosum volume
Rat brain injury mechanism identification through indentation experiment FE reconstruction
Experimental results: Volume variations
Cerebral spinal fluid volume
Rat brain injury mechanism identification through indentation experiment FE reconstruction
Experimental results: Volume variations
Abnormal cerebral grey matter volume
Rat brain injury mechanism identification through indentation experiment FE reconstruction
NUMERICAL
SIMULATIONS
Rat brain injury mechanism identification through indentation experiment FE reconstruction
Simulations: Model (mesh, 1)
Continuous mesh (Hypermesh 11.0)
Brain 118,016 hexahedrons
Skull
12,880 shells Brain/skull interface 25,760 hexahedrons
Rat brain injury mechanism identification through indentation experiment FE reconstruction
Simulations: Model (mesh, 2)
Rat brain injury mechanism identification through indentation experiment FE reconstruction
Simulations: Model (behaviour, 1)
The model is assumed to be Linear viscous elastic (Boltzman model) for brain Linear elastic for brain/skull interface With a rigid skull Homogeneous and isotropic
Material properties of the brain
Short term
shear modulus
Long term
shear modulus Time constant Density Bulk modulus
10 kPa 2 kPa 8 s 1,040 kg/m3 2.19 GPa
Rat brain injury mechanism identification through indentation experiment FE reconstruction
Simulations: Model (behaviour, 2)
Choice of material properties for the brain
Based on Fijalkowski et al. (2009)
In agreement with MRE data from Vappou et al. (2008)
Short term shear modulus Long term shear modulus
10 kPa 2 kPa
Rat brain injury mechanism identification through indentation experiment FE reconstruction
Simulations: Computed parameters
The model is submitted to indentation inputs Main computed parameters (Radioss)
Brain Von Mises stress Brain pressure CSF volume
Regions of interest
Vicinity of the corpus callosum Brain cortex Brain/skull interface
Rat brain injury mechanism identification through indentation experiment FE reconstruction
NUMERICAL
RESULTS
Rat brain injury mechanism identification through indentation experiment FE reconstruction
Results: Global view
Rat brain injury mechanism identification through indentation experiment FE reconstruction
Low impact group i.e. mild injury level
High impact group i.e. severe injury level
Cylinder displacement = 0.87 mm
Cylinder displacement = 2.62 mm
Results: Brain pressure (superficial)
Rat brain injury mechanism identification through indentation experiment FE reconstruction
Low impact group i.e. mild injury level
High impact group i.e. severe injury level
Maximal brain pressure = 798 kPa
Severe brain contusions
Maximal brain pressure = 3,206 kPa
Severe brain contusions
Results: Brain pressure (internal)
Rat brain injury mechanism identification through indentation experiment FE reconstruction
Low impact group i.e. mild injury level
High impact group i.e. severe injury level
Maximal brain pressure = 574 kPa
Severe brain contusions
Maximal brain pressure = 2,472 kPa
Severe brain contusions
Results: Brain Von Mises stress (superf.)
Rat brain injury mechanism identification through indentation experiment FE reconstruction
Low impact group i.e. mild injury level
High impact group i.e. severe injury level
Maximal brain Von Mises stress = 9 kPa
No neurological injuries
Maximal brain Von Mises stress = 27 kPa
Mild neurological injuries
Results: Brain Von Mises stress (internal)
Rat brain injury mechanism identification through indentation experiment FE reconstruction
Low impact group i.e. mild injury level
High impact group i.e. severe injury level
Maximal brain Von Mises stress = 8 kPa
No neurological injuries
Maximal brain Von Mises stress = 27 kPa
Mild neurological injuries
Results: CSF volume
Rat brain injury mechanism identification through indentation experiment FE reconstruction
Low impact group i.e. mild injury level
High impact group i.e. severe injury level
Low compression of CSF Delayed mild increase of CSF
volume ?
High compression of CSF Delayed severe increase of CSF
volume ?
CONCLUSIONS
Rat brain injury mechanism identification through indentation experiment FE reconstruction
FEM of the rat’s head including anatomical structures for in-vivo mild and severe TBI investigation through reconstruction of identation tests
Good correlation between brain Von Mises stresses distributions level, as well as brain pressure distributions level, and histological observations
TISSUE-LEVEL STRESSES WITHIN THE BRAIN DURING ROTATIONALLY-INDUCED mTBI: A 3D FINITE ELEMENT MODEL OF THE RAT COUPLED WITH EXPERIMENTS
Rat brain injury mechanism identification through indentation experiment FE reconstruction
Main conclusions
Future developments (1)
Expanding the range of existing simulations with new inputs &/or new protocols, espacially from an injury identification point of view
Achieving a more detailed mechanical characterization of the intracranial medium, i.e. taking into account inhomogeneity, anatomically based distribution, … In the long term, transfering the results to human brain, in order to propose some new injury criteria so as to improve human head protection devices
Rat brain injury mechanism identification through indentation experiment FE reconstruction
Future developments (2)
New challenge: predict delayed injuries thanks to Calculated mechanical parameters during loading Simulations that can reproduce hours of physiological evolutions
Rat brain injury mechanism identification through indentation experiment FE reconstruction
THANK YOU FOR
YOUR ATTENTION
Rat brain injury mechanism identification through indentation experiment FE reconstruction
Rat brain injury mechanism identification through indentation experiment FE
reconstruction
D. BAUMGARTNER, M. LAMY, R. WILLINGER DEPARTMENT OF FLUID AND SOLID MECHANICS
STRASBOURG UNIVERSITY – FRANCE
M. GILCHRIST DEPARTMENT OF MECHANICAL ENGINEERING
UNIVERSITY COLLEGE DUBLIN – IRELAND