ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

MECHANICAL EFFECT ON METABOLIC TRANSPORT AND CELL
VIABILITY IN THE INTERVERTEBRAL DISC
1. ABSTRACT
A. Malandrino 1 , J. Noailly 2 and D. Lacroix 2,3
The degeneration process in the intervertebral disc (IVD) is linked to progressive cell
death and to mechanical factors. Therefore, the inclusion of cell viability criteria
coupled with disc mechanics in a computational model would enable to get a better
understanding of the degeneration process in IVD.
A recently developed finite element (FE) model of the L4-L5 IVD based on
poromechanics and IVD metabolism (Malandrino et al., 2011) was modified to include
an exponential decay of cells over time below critical glucose and pH levels. The
implementation was verified against in vitro literature data on cell viability. Viability
criteria were used in the IVD model where diffusions of glucose, oxygen and lactate
accounted for predicted porosity and volume changes. Subtissue-specific mechanical
properties and cell concentrations were modelled. Daily compressive phases (standing
and resting) were applied. Metabolite boundary concentrations were reduced at the
endplates to induce critical conditions within the IVD. Solutions with and without
mechanical coupling were compared.
Critical glucose rather than pH levels were relevant to cell viability far away from the
solute supply. Deformation couplings increased glucose in the disc centre so that cells
stopped dying up to 10 hours earlier over two days simulated when mechanical
deformations were considered. These results can help in the understanding of coupled
mechanical and biological factors. If metabolite supply is disturbed, as it could happen
during endplate calcification or circulatory diseases, a local accelerated cell death in the
disc centre may occur in absence of tissue compliance. This study highlights the need to
restore both nutritional and mechanical factors in order to favour cell viability along
regenerative treatments.
2. INTRODUCTION
The study of cell death within the intervertebral disc (IVD) enables to understand better
the process of disc degeneration. Recently, a model simulating the coupling between
mechanical loading and the transport of metabolites has shown the effect of mechanics
on transport (Malandrino et al., 2011). However, modelling the link between
solute/metabolism concentrations and cell activity is still an open issue. In the literature
1
PhD candidate, Biomechanics and Mechanobiology Group, Institute for Bioengineering of Catalonia,
Baldiri Reixac 4, 08028 Barcelona, Spain
2
Senior Researcher, Biomechanics and Mechanobiology Group, Institute for Bioengineering of Catalonia,
Baldiri Reixac 4, 08028 Barcelona, Spain
3
Professor, Department of Mechanical Engineering, University of Sheffield, Mappin Street, Sheffield, S1
3JD, UK