Microstructure-informed biphasic-osmotic modeling of intervertebral disc degeneration

Area of Science:

• Biomechanics
• Computational Biology
• Biomaterials Science

Background:

• The intervertebral disc (IVD) is crucial for spinal load bearing.
• Its mechanical function depends on annulus fibrosus (AF) anisotropy, nucleus pulposus (NP) osmotic swelling, and fluid flow.
• Existing computational models often fail to integrate these coupled mechanisms with degeneration.

Purpose of the Study:

• To develop a microstructure-informed, degeneration-sensitive finite element model of the human IVD.
• To integrate regional fiber architecture, biphasic fluid-solid interactions, and osmotic swelling.
• To simulate degenerative changes and their impact on IVD mechanics.

Main Methods:

• A multiscale calibration strategy using mechanical experiments to determine model parameters.
• Incorporation of macroscopic (height loss) and microscopic (fiber uncrimping, proteoglycan depletion, porosity) degenerative changes.
• Simulation of physiological loading scenarios (lying, standing, trunk motion).

Main Results:

• The model successfully integrates AF anisotropy, NP osmotic swelling, and fluid transport.
• It captures macroscopic and microscopic degenerative changes in the IVD.
• Simulations reveal evolving mechanical contributions of IVD constituents with degeneration under various loading conditions.

Conclusions:

• The developed framework provides a mechanistic understanding of IVD degeneration.
• It defines parameter sets for different degenerative states, enabling patient-adapted modeling.
• The model offers insights into degeneration-dependent mechanical responses and loading sensitivities for improved mechanobiological understanding.