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

THE DESIGN OF A SIX-AXIS BIOREACTOR FOR THE APPLICATION OF COMPLEX, DAILY ACTIVITY PROFILES TO WHOLE-ORGAN INTERVERTEBRAL DISC CULTURES (#77)

Daniela Lazaro-Pacheco 1 , Isabelle Ebisch 1 , Michael Ward 1 , Timothy P Holsgrove 1
  1. Department of Engineering, University of Exeter, Exeter, Devon, United Kingdom

INTRODUCTION

Low back pain is commonly associated with degeneration of the intervertebral disc (IVD). The interaction between the mechanical and biochemical environments of the IVD is of increasing interest to better understand degenerative mechanisms, and evaluate treatments including regenerative therapies. Previous studies that have integrated mechanical loading into whole-organ IVD culture systems have shown that different loading conditions affect cell viability and cellular responses [1-3]. However, while there have been calls for more physiologically relevant loading to be integrated into such culture systems [4, 5], no current systems can apply the complex six-axis loads that occur during activities of daily living. Six-axis test systems used for spine research have generally been limited to biomechanical tests using stiffness matrix or pure moment protocols, and previous attempts to replicate activities of daily living have led to substantial errors, even using synthetic specimens [6]. Therefore, the aim of this research was to develop a custom six-axis bioreactor with the capability to apply complex six-axis loads to whole-organ IVD cultures.

METHODS

The six-axis test system (Figure 1) was based on previous designs [7, 8] with the addition of a custom biochamber to allow the maintenance of temperature and CO2 levels, provide circulating test media to the specimen, and provide a specimen clamping system to enable complex six-axis loading to be applied without compromising IVD nutrition. The control architecture and control model was also updated to improve control, and provide real-time load transformation from the load cell datum to the centre of the superior vertebral body.

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Figure 1. (a) The six-axis bioreactor; (b) the biochamber with a specimen mounted and media circulating; (c) an exploded view of the biochamber design.

Twenty activities of daily living from the Orthoload database [9] were applied to bovine tail specimens (n=6) to evaluate the system capability. Loads were scaled based on the IVD cross-sectional area, and the load profile was slowed down to minimise oscillations and vibration due to load coupling between axes. The root-mean-squared error was calculated to determine the ability of the system to track desired loads.

RESULTS

The desired load profile was closely matched for all 20 activities of daily living, and the root-mean-squared error was maintained within two-times the noise floor of the load cell. The mean root-mean-squared errors across all activities were 0.55N and 0.53N in anterior-posterior and lateral shear respectively, 1.62N in axial compression, and 0.01Nm in all rotational axes (lateral bending, flexion-extension, axial rotation).

DISCUSSION

The six-axis bioreactor builds on previous research into test systems for complex loading of the spine [7, 8], and combines it with the capability to complete whole-organ IVD culture tests, which has not previously been achieved. While the present study tested activities of daily living at a reduced test rate, these rates were similar to previous simplified pure moment testing protocols (0.1-0.3Hz). Therefore, this system provides a step forward for future research into both biomechanical and mechanobiological research, and provides novel data to inform how the system may be used in future studies at physiological test rates.

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  2. Chan et al, 2013. PLoS One, 8(8): pe72489.
  3. Korecki et al, 2007. Eur Spine J, 16(7): p1029-1037.
  4. Lazaro-Pacheco et al, 2023. APL Bioeng, 7(2): p021501.
  5. Pfannkuche et al, 2020. Connect Tissue Res, 61(3-4): p304-321.
  6. Holsgrove. 3rd International Workshop on Spine Loading and Deformation, 2019. Berlin, Germany.
  7. Holsgrove et al, 2017. Medical Engineering & Physics, 41: p74-80.
  8. Holsgrove et al, 2014. The Spine Journal, 14(7): p1308-1317.
  9. Bergmann, 2008. Orthoload. Charité Universitaetsmedizin Berlin.