A multiscale finite element model of fluid-microstructure interactions in human intervertebral disc compression

Area of Science:

• Biomechanics
• Computational Modeling
• Spine Research

Background:

• The human intervertebral disc (IVD) is a complex structure essential for spinal function.
• Existing computational models struggle to capture the IVD's nonlinear, time-dependent, and anisotropic mechanical behavior.
• Understanding IVD mechanics is crucial for addressing spine degeneration and injury.

Purpose of the Study:

• To develop and validate a multiscale biphasic finite element model of the entire human intervertebral disc (IVD).
• To integrate the heterogeneous, anisotropic, and fluid-solid coupled properties of the nucleus pulposus (NP), annulus fibrosus (AF), and cartilaginous endplates (CEPs).
• To investigate the influence of fluid-microstructure interactions on IVD mechanics under various loading conditions.

Main Methods:

• Extended a validated biphasic finite element model of the AF to a full-scale IVD model.
• Incorporated collagen fiber networks and interlamellar structures within the AF.
• Employed a multiscale identification strategy linking microstructural properties to macroscopic behavior and an automated meshing approach for geometric variations.
• Validated the model against experimental data under compressive creep-recovery, cyclic compression, and stepwise compression-relaxation protocols.

Main Results:

• The model accurately reproduced global and regional IVD mechanics, including energy absorption and strain-rate sensitivity.
• Numerical results demonstrated the significant role of fluid-microstructure interactions in governing IVD behavior.
• Key experimental factors like preload duration, hydration, and geometry were evaluated, revealing their influence on IVD response.

Conclusions:

• The validated multiscale biphasic finite element model provides a robust computational foundation for simulating human IVD biomechanics.
• The model successfully captures the complex, time-dependent behavior driven by fluid-microstructure interactions.
• This predictive framework advances understanding of IVD degeneration and supports future clinical applications in spine health.