Meeting Abstract
P3.69 Tuesday, Jan. 6 Some Tissues Like It Fast: Dynamic, Low Magnitude, High Frequency Analysis of Viscoelastic Tissues SZARKO, M.J.*; BERTRAM, J.E.A.; University of Calgary; University of Calgary mjszarko@ucalgary.ca
As limbs strike the ground during terrestrial movement ground reaction forces composed of relatively high frequency transient stress waves (over 100 Hz during human heel strike) travel up the skeleton. Many natural shock-absorbing structures within the musculoskeletal system have viscoelastic, time-dependent behaviours that may be sensitive to this high frequency loading, especially if compromised by over-use, over-loading or disease. Identification of loading-rate dependent behaviour, non-destructive low amplitude (0.01 MPa) dynamic compression tests were used. Loading involved 0.1-100 Hz equal amplitude sinusoidal waveforms periodic in the time record. Storage and loss moduli derived from load-deformation results allowed the calculation of both complex stiffness and hysteretic energy loss. As a model, articular cartilage was used to characterize loading-rate dependent behaviours of viscoelastic tissues. Investigating an osteoarthritic disease model of articular cartilage revealed that an intact collagen network is critical for normal hysteresis, above 30 Hz. Identifying mechanical freeze-thaw effects on articular cartilage found lower frequency (<20Hz) hysteretic differences for tissues stored at -20 oC and high frequency differences for tissues snap frozen in liquid nitrogen and stored at -80 oC. Sodium movement in articular cartilage, hypothesized as a cause for the altered biomechanics caused by freeze-thaw was assessed by exposure to a range of sodium concentrations. Stiffness decreased at lower frequencies (<20Hz) at 1M NaCl, but increased at higher frequencies (40-59 Hz) at 5M NaCl. The loading-rate sensitivity found in articular cartilage may be applicable to other viscoelastic musculoskeletal tissues and reveals low magnitude, high frequency dynamic testing as a new avenue for discovering novel tissue responses to the physiological range of loading rates.
