Strain transfer in the annulus fibrosus under applied flexion

Area of Science:

• Biomedical Engineering
• Cellular Mechanics
• Tissue Engineering

Background:

• Understanding the cellular-scale mechanical environment of the intervertebral disc is vital for developing effective tissue engineering strategies.
• Mechanical factors play a significant role in the pathology of intervertebral disc degeneration.

Purpose of the Study:

• To measure and compare macroscale and microscale strains within the outer annulus fibrosus of intact intervertebral discs.
• To investigate these strains across different cellular regions under varying flexion angles.

Main Methods:

• Utilized novel confocal microscopy techniques for dual labeling of cells and extracellular matrix.
• Measured macroscale surface strains on the annulus fibrosus.
• Contrasted surface strains with in situ microscale strains.

Main Results:

• Fiber-oriented surface strains were higher than in situ fiber strains, indicating load redistribution.
• Strain non-uniformity and matrix distortion occurred early and varied little with increased flexion, highlighting inter-fiber shear importance.
• Fiber-oriented intercellular strains were significantly larger and compressive, suggesting a unique pericellular mechanical environment.

Conclusions:

• The study provides novel insights into the complex in situ micro-mechanical environment of the annulus fibrosus.
• This knowledge is essential for understanding the mechanobiological behavior of intervertebral disc tissue.
• Further research into pericellular region morphology is needed to fully elucidate strain transfer pathways.