A Novel Method for Repeatable Failure Testing of Annulus Fibrosus

[+] Author and Article Information
Benjamin Werbner

University of California, Berkeley, Mechanical Engineering Department, 2162 Etcheverry Hall, #1740, Berkeley, CA 94720-1740

Minhao Zhou

University of California, Berkeley, Mechanical Engineering Department, 2162 Etcheverry Hall, #1740, Berkeley, CA 94720-1740

Grace O'Connell

University of California, Berkeley, Mechanical Engineering Department, 5122 Etcheverry Hall, #1740, Berkeley, CA 94720-1740

1Corresponding author.

ASME doi:10.1115/1.4037855 History: Received April 28, 2017; Revised September 01, 2017


Tears in the annulus fibrosus (AF) of the intervertebral disc can result in herniation of the nucleus pulposus and progressive disc degeneration. Understanding AF failure mechanics is particularly important as research moves towards developing biological repair strategies for herniated discs. Unfortunately, failure mechanics of fiber-reinforced tissues, particularly those with fibers oriented off-axis from the applied load, is not well understood. Therefore, the objective of this study was to investigate the effectiveness of mid-length notch geometries in producing repeatable and consistent tissue failure within the gauge region of AF mechanical test specimens. Finite element models (FEMs) representing several notch geometries were created to predict the location of bulk tissue failure using a local strain-based criterion. FEM results were then validated by experimentally testing a sub-set of the modeled specimen geometries. Mechanical testing data agreed well with model predictions (~90% agreement), validating the predictive power of the model. Two of the modified dog-bone geometries ('Half' and 'Quarter') effectively ensured tissue failure at the mid-length for specimens oriented along the circumferential-axial and circumferential-radial directions. The variance of mechanical properties measured was significantly lower for notched samples that failed at the mid-length, suggesting that mid-length notch geometries result in more consistent and reliable data. In addition, the approach developed in this study provides a framework for evaluating failure properties of other fiber-reinforced tissues, such as tendons and meniscus.

Copyright (c) 2017 by ASME
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