A Comparison of Uniaxial and Biaxial Mechanical Properties of the Annulus Fibrosus: A Porcine Model

This study compared the uniaxial and biaxial tensile mechanical behavior of porcine annulus fibrosus tissue to better reflect the multidirectional loading experienced by the intervertebral disc in vivo. Two-layer annular samples harvested from anterior and posterior, superficial and deep regions were subjected to uniaxial, constrained uniaxial, and biaxial deformation to a stretch ratio of 1.23. Biaxial loading produced significantly higher stress–stretch moduli and peak stresses compared to both uniaxial conditions, while no significant mechanical differences were observed between tissue locations. These findings demonstrate that annulus fibrosus tissue experiences substantially higher stresses under multidirectional loading, underscoring the importance of biaxial testing for accurate disc biomechanics modeling.