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DAMPING PROPERTIES OF THE NUCLEUS PULPOSUS
S562
Presentation 1032 − Topic 39. Soft tissue biomechanics
DAMPING PROPERTIES OF THE NUCLEUS PULPOSUS Arne Vogel, Dominique P. Pioletti
Laboratory of Biomechanical Orthopedics, EPFL, Switzerland
Introduction While the elastic aspect of the nucleus pulposus (NP) has been well described [Aladin, 2010], the viscous properties of the NP are far less studies with the exception of some studies [Boxberger, 2009; Iatridis, 1997]. In particular at large dynamic physiological strains and in unconfined situation, there is virtually no information on the NP viscous behaviour. The objective of the present study is to introduce a reliable method to address the damping properties of hydrogels under large and physiological deformations. As particular example, the damping properties of the coccygeal bovine nucleus pulposus are investigated.
work absorbed per cycle divided by the work input per cycle. For a viscoelastic material, it directly represents the fraction of energy that is dissipated into heat.
Results The dependency of on frequency is given in figure 2. The specific damping capacity at 0.1 Hz is significantly lower than the values at 0.01 and 10 Hz, suggesting a minimum of the specific damping capacity between those frequencies
Methods Six tails from 12 months bovine were acquired from the local slaughterhouse. The NP of the largest coccygeal disc were excised in the axial direction using a 7 mm diameter biopsy punch. The samples were tested on a standard tension machine (Electropulse E3000, Instron, USA), equipped with specially designed fixtures (Fig 1).
Figure 2: The specific damping capacity of the nucleus pulposus is dependent on frequency. at 0.1 Hz is significantly lower than the values at 0.01 and 10 Hz.
Discussion
Figure 1: Mechanical testing system. The encapsulation device is clamped between two special fixtures that allow for perfusion of PBS. (Up) the sample setup with perfusion. (down) the control setup with a syringe controlling the amount of PBS in the encapsulation device. The deformation of the sample is monitored using a camera. These fixtures firmly grip the encapsulation device and perfuse PBS through the device’s porous filters to keep the sample hydrated and at a temperature of 21°C. The tests were performed in sinusoidal strain amplitude control mode reaching a total of 12.5% of compressive strain. Four different frequencies were tested: 102, 101, 100, 101 Hz. Following the work of Lee [Lee, 1998], we propose to define the specific damping capacity as the Journal of Biomechanics 45(S1)
The results of this work are consistent with previous work [Leahy, 2001] in that dissipation tends to be lower at values neighbouring 0.1 and 1 Hz. These frequencies correspond to the dynamics of loads in all day activities such as walking. It is, therefore, interesting to observe that for higher frequencies the NP would contribute more to dampen vibration energies of the spine. This work introduces a reliable method to measure the specific damping capacity of soft biological materials in large deformation and nonlinear regimes. In contrast to classical rheology techniques, the developed method has the advantage to work on the energetical level, which is well appropriate to study materials in nonlinear regimes.
References Aladin, et al., J Orthop Res, 28:497–502, 2010. Boxberger, et al., J Orth Res, 24:1906–1915, 2006. Iatridis, et al., J Biomech, 30:1005–1013, 1997. Leahy, et al., J Mat Sc:Mat Med, 12:689–692, 2001 Lee, et al., J Sound Vibration, 211:265–272, 1998.
ESB2012: 18th Congress of the European Society of Biomechanics
Presentation 1032 − Topic 39. Soft tissue biomechanics
DAMPING PROPERTIES OF THE NUCLEUS PULPOSUS Arne Vogel, Dominique P. Pioletti
Laboratory of Biomechanical Orthopedics, EPFL, Switzerland
Introduction While the elastic aspect of the nucleus pulposus (NP) has been well described [Aladin, 2010], the viscous properties of the NP are far less studies with the exception of some studies [Boxberger, 2009; Iatridis, 1997]. In particular at large dynamic physiological strains and in unconfined situation, there is virtually no information on the NP viscous behaviour. The objective of the present study is to introduce a reliable method to address the damping properties of hydrogels under large and physiological deformations. As particular example, the damping properties of the coccygeal bovine nucleus pulposus are investigated.
work absorbed per cycle divided by the work input per cycle. For a viscoelastic material, it directly represents the fraction of energy that is dissipated into heat.
Results The dependency of on frequency is given in figure 2. The specific damping capacity at 0.1 Hz is significantly lower than the values at 0.01 and 10 Hz, suggesting a minimum of the specific damping capacity between those frequencies
Methods Six tails from 12 months bovine were acquired from the local slaughterhouse. The NP of the largest coccygeal disc were excised in the axial direction using a 7 mm diameter biopsy punch. The samples were tested on a standard tension machine (Electropulse E3000, Instron, USA), equipped with specially designed fixtures (Fig 1).
Figure 2: The specific damping capacity of the nucleus pulposus is dependent on frequency. at 0.1 Hz is significantly lower than the values at 0.01 and 10 Hz.
Discussion
Figure 1: Mechanical testing system. The encapsulation device is clamped between two special fixtures that allow for perfusion of PBS. (Up) the sample setup with perfusion. (down) the control setup with a syringe controlling the amount of PBS in the encapsulation device. The deformation of the sample is monitored using a camera. These fixtures firmly grip the encapsulation device and perfuse PBS through the device’s porous filters to keep the sample hydrated and at a temperature of 21°C. The tests were performed in sinusoidal strain amplitude control mode reaching a total of 12.5% of compressive strain. Four different frequencies were tested: 102, 101, 100, 101 Hz. Following the work of Lee [Lee, 1998], we propose to define the specific damping capacity as the Journal of Biomechanics 45(S1)
The results of this work are consistent with previous work [Leahy, 2001] in that dissipation tends to be lower at values neighbouring 0.1 and 1 Hz. These frequencies correspond to the dynamics of loads in all day activities such as walking. It is, therefore, interesting to observe that for higher frequencies the NP would contribute more to dampen vibration energies of the spine. This work introduces a reliable method to measure the specific damping capacity of soft biological materials in large deformation and nonlinear regimes. In contrast to classical rheology techniques, the developed method has the advantage to work on the energetical level, which is well appropriate to study materials in nonlinear regimes.
References Aladin, et al., J Orthop Res, 28:497–502, 2010. Boxberger, et al., J Orth Res, 24:1906–1915, 2006. Iatridis, et al., J Biomech, 30:1005–1013, 1997. Leahy, et al., J Mat Sc:Mat Med, 12:689–692, 2001 Lee, et al., J Sound Vibration, 211:265–272, 1998.
ESB2012: 18th Congress of the European Society of Biomechanics