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Articular cartilage

Viscoelastic properties of articular cartilage at high frequencies Geoffrey R Fulcher David WL Hukins Duncan ET Shepherd School of Mechanical Engineering University of Birmingham. Articular cartilage. Low friction & wear Transmitting forces Deformable: larger areas - lower stress.

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Articular cartilage

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  1. Viscoelastic properties of articular cartilage at high frequenciesGeoffrey R FulcherDavid WL HukinsDuncan ET ShepherdSchool of Mechanical EngineeringUniversity of Birmingham

  2. Articular cartilage • Low friction & wear • Transmitting forces • Deformable: larger areas - lower stress

  3. Articular cartilage • Viscoelastic • Behaviour under the full range of physiological loading frequencies?

  4. Rise time of heel strike force • Generally • 100-150 ms • Some people • 5-25 ms • implicated in the onset of osteoarthritis

  5. 1 Hz • rise time 500 ms • 90 Hz • rise time 5.6 ms

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

  7. Viscoelasticity

  8. Viscoelasticity • phase angle of 0° • material is purely elastic • phase angle of 90° • material is purely viscous

  9. 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)

  10. Materials & methods • Bovine • Tibial plateau • Fluid bath • Indenter

  11. Materials & methods • Bose ElectroForce 3200 testing machine • WinTest • DMA (Dynamic Mechanical Analysis)

  12. Materials & methods • sinusoidally varying compressive force of between 16 N and 36 N • 1.7 MPa • 1 to 90 Hz • Calculated: • E´ • E´´ • 

  13. Results

  14. Results

  15. Storage modulus • Curve fit • Slope

  16. Phase angle •  > 0 for all frequencies 1 to 90 Hz • 3.4 to 5.7° (mean = 4.9°, SD = 0.6°) • Viscoelastic

  17. 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

  18. Implications for osteoarthritis? 1 Hz 100 Hz 10 Hz

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

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

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