Mechanical properties of chondrocytes from micropipette aspiration experiments

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Mechanical properties of chondrocytes from
micropipette aspiration experiments
Frank Baaijens1, Wendy Trickey2, Tod Laursen3,
Leonidas Alexopoulos2 and Farshid Guilak2 1
Department of Biomedical Engineering, Eindhoven
University of Technology 2 Departments of
Surgery and Biomedical Engineering, Duke
University 3 Department of Civil Engineering,
Duke University
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Micro-pipette aspiration experiment
PA
FA
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Time dependent response
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Questions

• Mechanical properties of chondrocytes
• viscoelastic?
• bi-phasic?
• compressibility?
• finite strains?

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Constitutive modeling
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Approximate analytical solution

• Theret et al solution
• final aspiration length
• linear elastic, infinitesimal strains
• incompressible
• half-space approximation

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Deformation of chondrocyte
Incompressible neo Hookean model
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Finite strains?
Infinitesimal strains Haider, Guilak et al (2002)
Finite strains
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Theret approximation half space?
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Creep response
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Compressibility of chondrocytes
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Recovery experiment
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Compression
Bi-phasic, compressible, viscoelastic
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Equilibration
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Recovery
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Results
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Discussion

• Chondrocytes are compressible (? 0.4)
• Bi-phasic theory can not explain time dependent
  response of chondrocytes
• Creep response due to viscoelastic behavior
• Estimated time scales of PA and FA do not match
  different parts of cells are involved in PA and
  FA

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Parameter estimation
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Theret approximation bi-phasic?
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Compression and Recovery
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Creep recovery