Material properties of bovine intervertebral discs across strain rates

• Published in: Journal of the mechanical behavior of biomedical materials Vol. 65; pp. 824 - 830
• Main Authors: Newell, Nicolas, Grigoriadis, Grigorios, Christou, Alexandros, Carpanen, Diagarajen, Masouros, Spyros D.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier Ltd 01.01.2017
• Subjects: Algorithms; Animals; Biomechanical Phenomena; Cattle; Collagen fibre; Elastic Modulus; Finite Element Analysis; Finite element modelling; Intervertebral disc; Intervertebral Disc - physiology; inverse methods; Lumbar Vertebrae - physiology; material properties; spine; Stress, Mechanical; Finite element modelling; spine; material properties; Intervertebral disc; Collagen fibre; inverse methods
• DOI: 10.1016/j.jmbbm.2016.10.012
• ISSN: 1751-6161; 1878-0180

The intervertebral disc (IVD) is a complex structure responsible for distributing compressive loading to adjacent vertebrae and allowing the vertebral column to bend and twist. To study the mechanical behaviour of individual components of the IVD, it is common for specimens to be dissected away from their surrounding tissues for mechanical testing. However, disrupting the continuity of the IVD to obtain material properties of each component separately may result in erroneous values. In this study, an inverse finite element (FE) modelling optimisation algorithm has been used to obtain material properties of the IVD across strain rates, therefore bypassing the need to harvest individual samples of each component. Uniaxial compression was applied to ten fresh-frozen bovine intervertebral discs at strain rates of 10-3–1/s. The experimental data were fed into the inverse FE optimisation algorithm and each experiment was simulated using the subject specific FE model of the respective specimen. A sensitivity analysis revealed that the IVD's response was most dependent upon the Young's modulus (YM) of the fibre bundles and therefore this was chosen to be the parameter to optimise. Based on the obtained YM values for each test corresponding to a different strain rate (ε̇), the following relationship was derived:YM=35.5lnε̇+527.5. These properties can be used in finite element models of the IVD that aim to simulate spinal biomechanics across loading rates.