Full-field strain measurement and material

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Centre for Biomedical and Healthcare Engineering CNRS UMR 5307

Mr Aaron Romo, Prof Stéphane Avril, Dr Pierre Badel, Dr Ambroise Duprey, Prof

Jean-Pierre Favre, Prof Sam Evans

Full-field strain measurement and material

identification in soft tissue biomechanics

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BSSM Cardiff - 2013/09/05 - Stéphane AVRIL

Location

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Center for Biomedical and Healthcare Engineering

Campus with hospital, medical school, prevention center, college of engineering and companies manufacturing

medical devices

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4 topics

22 permanent staff 35 postgraduate

students and postdocs

Soft tissue

biomechanics

Biomaterials for bone

replacement Healthcare

engineering

Biotoxicity of inhaled

nanoparticules

(5)

5

Biomechanics of soft tissues

The aim is to employ biomechanical models to adapt the treatments of cardiovascular and osteoarticuar diseases to each patient

Orthèses fonctionnelles

Orthèses de rééducation

Orthèses prophylactiques

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Today’s talk…

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ascending aorta

descending aorta

(thoracic aorta and abdominal aorta)

arch of aorta ▶ a local dilation of the aorta

due to aortic wall weakening

a fatal medical emergency aneurysm rupture

Aortic aneurisms

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Aortic aneurisms

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PREVENTION OF ATAA RUPTURE FROM A

BIOMECHANICAL

POINT OF VIEW???

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Quantify the risk of rupture for each patient…

[McGloughlin T. Biomechanics and mechanobiology of aneurysms. 2012, Springer

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2 IMPORTANT QUESTIONS

What are the patient-specific material properties of the

tissue?

What is the patient-specific strength of the tissue?

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BIOMECHANICAL EXPERIMENTAL

APPROACHES

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Tensile rupture mode

[Duprey et. al., In-vitro characterisation of physiological and

maximum elastic modulus of ascending thoracic aortic aneurysms using uniaxial tensile testing, Eur. J. Vascular &

Endovascular Surgery, 2010]

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Arteries: a complex structure and

behavior

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Biomechanical comparison of aneurismal and healthy tissue

Vorp DA, Schiro BJ, Ehrlich MP, Juvonen TS, Ergin MA, Griffith BP. Effect of aneurysm on the tensile strength and biomechanical behaviour of the ascending thoracic aorta. Ann Thorac Surg 2003; 75(4):1210-4.

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Need of biaxial tension

Sacks MS. Biaxial mechanical evaluation of planar biological materials. J. Elast. 61:199–246, 2000

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W < 10 mJ/cm ²

Sommer G, Gasser TC, Regitnig P, Auer M., Holzapfel G.A. Dissection properties of the human aortic media: an experimental study. ASME J Biomech Eng 2008; 130:021007.

Delamination properties…

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Lack of local analyses

Where and how does the rupture initiates?

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MATERIALS AND

METHODS

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Deformation gradient Lagrange strain

Aneurismal

aortic tissue Inflation test Optical Full-field measurement ( Full-field displacement)

Inverse procedure

Full-field

Stress reconstruction

Constitutive model

Calculation of stress at rupture

Methodology

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Deformation gradient Lagrange strain

Aneurismal

aortic tissue Inflation test Optical Full-field measurement ( Full-field displacement)

Inverse procedure

Full-field

Stress reconstruction

Constitutive model

Calculation of stress at rupture

Methodology

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Materials

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Deformation gradient Lagrange strain

Aneurismal

aortic tissue Inflation test Optical Full-field measurement ( Full-field displacement)

Inverse procedure

Full-field

Stress reconstruction

Constitutive model

Calculation of stress at rupture

Methodology

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inflation device cylinder

pressure gage

in vivo loading environments

(biaxial stress state due to internal pressure) can be generated

Inflation test

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Deformation gradient Lagrange strain

Aneurismal

aortic tissue Inflation test Optical Full-field measurement ( Full-field displacement)

Inverse procedure

Full-field

Stress reconstruction

Constitutive model

Calculation of stress at rupture

Methodology

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camera

Instron machine protector

Undeformed Deformed

x y

tracks the gray value pattern

in each subset during deformation

Digital image stereocorrelation

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Deformation gradient Lagrange strain

Aneurismal

aortic tissue Inflation test Optical Full-field measurement ( Full-field displacement)

Inverse procedure

Full-field

Stress reconstruction

Constitutive model

Calculation of stress at rupture

Methodology

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Theory of finite deformation

Deformation gradient F

Green-Lagrange strain tensor E = 1/2(C - I) right Cauchy-Green tensor C = F ^T F

Ux Uy Uz

from the undeformed and deformed

coordinates of each measurement data point

Assumption: plane stress

homogeneous initial thickness incompressibility

Measured displacement fields

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Derivation of the strain fields

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ℎ = ℎ ₀

𝑭 _𝟏𝟏 𝑭 _𝟐𝟐 − 𝑭 _𝟏𝟐 𝑭 _𝟐𝟏 Thickness evolution

Incompressibility assumption:

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Deformation gradient Lagrange strain

Aneurismal

aortic tissue Inflation test Optical Full-field measurement ( Full-field displacement)

Inverse procedure

Full-field

Stress reconstruction

Constitutive model

Calculation of stress at rupture

Methodology

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Stress reconstruction

 Membrane elastostatics

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Validation

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Deformation gradient Lagrange strain

Aneurismal

aortic tissue Inflation test Optical Full-field measurement ( Full-field displacement)

Inverse procedure

Full-field

Stress reconstruction

Constitutive model

Calculation of stress at rupture

Methodology

S. Avril, P. Badel, A Duprey. Anisotropic and hyperelastic identification of in vitro human arteries from full-field

measurements. Journal of Biomechanics -2010, vol 43, N°15, pp 2978-2985.

J. Kim, S. Avril, A Duprey, JP Favre. Experimental characterization of rupture in human aortic aneurysms using full-field

measurement technique. Biomechanics and Modeling in Mechanobiology, 2012.

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Incompressibility:

J =1

Constitutive model

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Point-wise stress-strain curve fitting

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RESULTS

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Results

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Local distribution of material

properties

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Statistical analysis of the results

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Ultimate stresses

inflation device

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Rupture modes

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Rupture initiation

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Conclusions

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Modes of rupture???

The tissue thinning starts to localize very early before the rupture

-> presence of aneslatic response in very local areas

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Conclusions

 The strength of the tissue is heterogeneous

 Existence of weaker zones in the tissue

 Damage develops in the weaker zones

 Damage leads to rupture when the pressure increases.

 What is the microstructural specificity of the weaker zone?

 Does it affect the elastic response in the

physiological domain?

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Current questions…

inflation device

 Accurate measurement of the thickness distribution

 Validity of the incompressibility assumption

 Effect of loading conditions and environment

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Future work

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Microscopic analysis

Multiphoton-second harmonic generation (MP-SHG) microscope 600x

Intima Media

Smooth muscle cells Elastin fibers

Collagen fibers

Biologic sensor and filter

Adventitia Collagen fibers

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In vivo imaging

S. Avril, F. Schneider, C. Boissier, ZY Li. In vivo velocity vector imaging and time-resolved strain rate measurements in the wall of blood vessels using MRI. Journal of Biomechanics, 2010, 44(5) pp 979-983.

US elastography

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Full-field strain measurement and material

Centre for Biomedical and Healthcare Engineering CNRS UMR 5307

Mr Aaron Romo, Prof Stéphane Avril, Dr Pierre Badel, Dr Ambroise Duprey, Prof

Jean-Pierre Favre, Prof Sam Evans

Full-field strain measurement and material

identification in soft tissue biomechanics

Location

Center for Biomedical and Healthcare Engineering

Campus with hospital, medical school, prevention center, college of engineering and companies manufacturing

medical devices

4 topics

22 permanent staff 35 postgraduate

students and postdocs

Soft tissue

biomechanics

Biomaterials for bone

replacement Healthcare

engineering

Biotoxicity of inhaled

nanoparticules

Biomechanics of soft tissues

The aim is to employ biomechanical models to adapt the treatments of cardiovascular and osteoarticuar diseases to each patient

Today’s talk…

ascending aorta

descending aorta

(thoracic aorta and abdominal aorta)

arch of aorta ▶ a local dilation of the aorta

due to aortic wall weakening

a fatal medical emergency aneurysm rupture

Aortic aneurisms

Aortic aneurisms

PREVENTION OF ATAA RUPTURE FROM A

BIOMECHANICAL

POINT OF VIEW???

Quantify the risk of rupture for each patient…

2 IMPORTANT QUESTIONS

What are the patient-specific material properties of the

tissue?

What is the patient-specific strength of the tissue?

BIOMECHANICAL EXPERIMENTAL

APPROACHES

Tensile rupture mode

Arteries: a complex structure and

behavior

Biomechanical comparison of aneurismal and healthy tissue

Need of biaxial tension

W < 10 mJ/cm 2

Delamination properties…

Lack of local analyses

Where and how does the rupture initiates?

MATERIALS AND

METHODS

Deformation gradient Lagrange strain

Aneurismal

aortic tissue Inflation test Optical Full-field measurement ( Full-field displacement)

Inverse procedure

Full-field

Stress reconstruction

Constitutive model

Calculation of stress at rupture

Methodology

Deformation gradient Lagrange strain

Aneurismal

aortic tissue Inflation test Optical Full-field measurement ( Full-field displacement)

Inverse procedure

Full-field

Stress reconstruction

Constitutive model

Calculation of stress at rupture

Methodology

Materials

Deformation gradient Lagrange strain

Aneurismal

aortic tissue Inflation test Optical Full-field measurement ( Full-field displacement)

Inverse procedure

Full-field

Stress reconstruction

Constitutive model

Calculation of stress at rupture

Methodology

W < 10 mJ/cm ²

Green-Lagrange strain tensor E = 1/2(C - I) right Cauchy-Green tensor C = F ^T F

ℎ = ℎ ₀

𝑭 _𝟏𝟏 𝑭 _𝟐𝟐 − 𝑭 _𝟏𝟐 𝑭 _𝟐𝟏 Thickness evolution