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

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Presentation on theme: "Viscoelastic properties of articular cartilage at high frequencies Geoffrey R Fulcher David WL Hukins Duncan ET Shepherd School of Mechanical Engineering."— Presentation transcript:

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

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 10 Hz 100 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 Acknowledgements Arthritis Research Campaign Duncan ET Shepherd BEng, PhD, CEng, FIMechE School of Mechanical Engineering University of Birmingham


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