Viscoelastic properties of articular cartilage at high frequencies Geoffrey R Fulcher David WL Hukins Duncan ET Shepherd School of Mechanical Engineering University of Birmingham

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Viscoelastic properties of articular cartilage at
high frequencies Geoffrey R FulcherDavid WL
HukinsDuncan ET Shepherd School of Mechanical
EngineeringUniversity of Birmingham
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Articular cartilage

• Low friction wear
• Transmitting forces
• Deformable larger areas - lower stress

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Articular cartilage

• Viscoelastic
• Behaviour under the full range of physiological
  loading frequencies?

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Rise time of heel strike force

• Generally
• 100-150 ms
• Some people
• 5-25 ms
• implicated in the onset of osteoarthritis

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• 1 Hz
• rise time 500 ms
• 90 Hz
• rise time 5.6 ms

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Objective

• To measure the viscoelastic properties of bovine
  articular cartilage at loading frequencies of up
  to 90 Hz

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Viscoelasticity
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Viscoelasticity

• phase angle of 0
• material is purely elastic
• phase angle of 90
• material is purely viscous

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Viscoelastic material

• Storage modulus, E
• elastic part of the response (where energy is
  stored and used for elastic recoil of the
  specimen when a stress is removed)
• Loss modulus, E
• the viscous response (where energy is dissipated
  and the material flows)

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Materials methods

• Bovine
• Tibial plateau
• Fluid bath
• Indenter

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Materials methods

• Bose ElectroForce 3200 testing machine
• WinTest
• DMA (Dynamic Mechanical Analysis)

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Materials methods

• sinusoidally varying compressive force of between
  16 N and 36 N
• 1.7 MPa
• 1 to 90 Hz
• Calculated
• E
• E
• ?

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Results
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Results
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Storage modulus

• Curve fit
• Slope

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Phase angle

• ? gt 0 for all frequencies 1 to 90 Hz
• 3.4 to 5.7 (mean 4.9, SD 0.6)
• Viscoelastic

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Implications for osteoarthritis?

• More energy is stored by the tissue than is
  dissipated
• Effect is greater at higher frequencies.
• Main mechanism for this excess energy to be
  dissipated is by the formation of cracks

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Implications for osteoarthritis?
1 Hz
100 Hz
10 Hz
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Conclusions

• Articular cartilage is viscoelastic 1 to 90 Hz
• High frequency loading, seen in some of the
  population, may be implicated in osteoarthritis

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Acknowledgements

• Arthritis Research Campaign
• Duncan ET Shepherd BEng, PhD, CEng, FIMechE
• School of Mechanical Engineering
• University of Birmingham
• d.e.shepherd_at_bham.ac.uk
• www.bioeng.bham.ac.uk