Transient swelling behavior of the bovine caudal disc

Semih E Bezci; Kyelo Torres; Carlo Carraro; Dominic Chiavacci; Ben Werbner; Shiyin Lim; Grace D O'Connell

doi:10.1016/j.jmbbm.2020.104089

Transient swelling behavior of the bovine caudal disc

J Mech Behav Biomed Mater. 2020 Dec:112:104089. doi: 10.1016/j.jmbbm.2020.104089. Epub 2020 Sep 22.

Authors

Semih E Bezci¹, Kyelo Torres¹, Carlo Carraro², Dominic Chiavacci¹, Ben Werbner¹, Shiyin Lim¹, Grace D O'Connell³

Affiliations

¹ Department of Mechanical Engineering University of California, Berkeley, United States.
² Department of Chemical and Biomolecular Engineering University of California, Berkeley, United States.
³ Department of Mechanical Engineering University of California, Berkeley, United States; Department of Orthopaedic Surgery University of California, San Francisco, United States. Electronic address: g.oconnell@berkeley.edu.

PMID: 32998075
DOI: 10.1016/j.jmbbm.2020.104089

Abstract

The intervertebral disc is an avascular composite structure, comprised of the nucleus pulposus (NP) and the annulus fibrosus (AF). Previous tissue-level experiments either examined relative differences in swelling capacity of the two disc regions at a single time point or tested explant structures that did not replicate in situ boundary conditions. Previous joint-level studies that investigated time-dependent fluid flow into the disc provided limited information about swelling-induced intradiscal strains with respect to time and boundary constraints. Therefore, the objective of this study was to investigate time-dependent swelling behavior of the intervertebral disc ex situ. The first study investigated time-dependent free-swelling response of the whole disc and the disc's subcomponents separately (i.e., NP and AF). Findings from this study showed that the swelling rate and swelling capacity of NP explants under free-swelling conditions were greater than AF explants. The second study evaluated the effect of boundary conditions on in-plane strain distributions of intact discs and AF rings. Swelling-induced strain was highly heterogeneous in AF rings, where negative circumferential strains were observed in the inner AF and tensile circumferential strains were observed in the outer AF. Radial strains in AF rings were an order of magnitude greater than circumferential strains. Restricting fluid flow only to the outer AF periphery reduced the swelling of the inner AF. Swelling of intact discs affected both NP and AF swelling behaviors, where NP hydration decreased by 60%. Furthermore, the presence of the NP reduced peak radial strains in the AF and resulted in uniform strain distribution throughout the AF. In conclusion, these studies highlight that tissue hydration and swelling-induced strains largely depend on regional biochemical composition and geometric boundary constraints.

Keywords: Bovine disc; Digital image correlation; Image analysis; Intervertebral disc; Residual strain; Swelling.

Publication types

Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

Animals
Annulus Fibrosus*
Cattle
Intervertebral Disc Degeneration*
Intervertebral Disc*
Nucleus Pulposus*
Stress, Mechanical