Special Poster Session 50th International Society for the Study of the Lumbar Spine Annual Meeting 2024

COMPLEX, DYNAMIC, SIX-AXIS DAILY ACTIVITY PROFILES CREATE A MORE CHALLENGING ENVIRONMENT FOR INTERVERTEBRAL DISC CELLS THAN SINGLE-AXIS LOADING - AN IN VITRO STUDY USING A WHOLE-ORGAN INTERVERTEBRAL DISC CULTURE MODEL (#SP-1d)

Isabelle Ebisch 1 , Daniela Lazaro-Pacheco 1 , Justin Cooper-White 2 3 , Dominic J Farris 4 , Timothy P Holsgrove 1
  1. Department of Engineering, University of Exeter, Exeter, Devon, United Kingdom
  2. School of Chemical Engineering, The University of Queensland, Brisbane, Queensland, Australia
  3. The UQ Centre in Stem Cell Ageing and Regenerative Engineering (StemCARE), Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, Brisbane, Queensland, Australia
  4. Department of Public Health and Sports Sciences, University of Exeter, Exeter, Devon, United Kingdom

INTRODUCTION

Bioreactors that apply mechanical loading to whole-organ intervertebral disc (IVD) cultures provide a valuable bridge between simplified cell-culture and unloaded IVD-culture models, and more expensive, time-consuming, and less controllable in vivo studies [1]. Previous studies have shown that different loading conditions affect cell viability and cellular responses. However, these studies have been limited to uniaxial cyclic loading [2-4], or axial compression combined with torsion [5] or bending [6] using simplified loading at sub-physiological rates. The integration of complex, six-axis loading to simulate activities of daily living remains unexplored. Therefore, this study aimed to use a unique six-axis bioreactor to apply a population-based six-axis activity profile to IVD cultures, and compare the cell viability with single-axis loading, and unloaded controls.

METHODS

Bovine tail (Cx1-2) specimens were prepared and tested using the PrimeGrowth isolation/neutralization/culture system. Test groups (n=4) comprised: day 0 controls (D0); day 7 unloaded controls (D7); single-axis loading (1A), and six-axis loading (6A). D0 specimens were immediately dissected, and the cell viability of nucleus pulposus (NP) and annulus fibrosus (AF) tissue measured. The D7 group was cultured in a free-swelling condition. The 6A group was fixed into the bioreactor and a six-axis activity profile applied for 7 days. The profile (Figure 1) [7] was produced by combining Harmonised European Time Use Surveys data for a UK population aged 24-44 years [8], and six-axis load data from the Orthoload database [9]. The 1A group was fixed into the six-axis bioreactor in the same way as 6A specimens, and the same axial loading applied, with all other axes fixed. After 7 days, cell viability in the D7, 1A and 6A groups was measured.

 654e5b8933987-FIGURE_1.png

Figure 1. 24h activity profile for a UK population aged 24-44 years. Upper activities (light green) are moderate-high intensity, and the bottom activities (dark green) are sedentary-low intensity.

RESULTS

There were no significant differences in cell viability between D0 and D7 controls and the 1A group. However, there was a significant reduction in cell viability in the NP and AF in the 6A group compared to D0, D7, and 1A groups (Figure 2).

654e5b8933987-4_GROUPS_ISSLS+FIGURE_2.png

Figure 2. Cell viability was significantly reduced in the six-axis group (6A) compared to unloaded controls (D0 and D7) and the single-axis group (1A).

DISCUSSION

Increasing the axes used to load IVDs, or introducing a diurnal cycle compared to static loading has been shown to reduce cell viability [5, 6, 10]. However, this is the first study to combine a 24h six-axis activity profile, based on activities of daily living. While cell viability was not significantly altered compared to unloaded controls when the activity profile was limited to axial compression, applying the activity profile in six axes created a more challenging environment for IVD cells. Therefore, loads and kinematics that replicate physiological activities should be prioritised in IVD culture tests to provide relevant and translatable data for the clinical setting. The population-specific activity profile and six-axis bioreactor of this study provides a unique platform for research into IVD mechanobiology, which has not previously been possible.

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