Bovine annulus fibrosus hydration affects rate-dependent failure mechanics in tension |
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Institution: | 1. School of Mechanical Engineering, The Fleischman Faculty of Engineering, Tel Aviv University, Tel Aviv 69978, Israel;2. Institute of Orthopaedic Research and Biomechanics, University of Ulm, Helmholtzstrasse 14, 89081 Ulm, Germany;3. IRCCS Galeazzi Orthopaedic Institute, via Galeazzi 4, 20161 Milan, Italy;4. Department of Internal Medicine II, University Hospital Ulm, Albert-Einstein-Allee 23, 89081 Ulm, Germany;5. Core Facility Small Animal MRI, Medical Faculty, Ulm University, Albert-Einstein-Allee 11, 89081 Ulm, Germany |
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Abstract: | The high water content of the intervertebral disc is essential to its load bearing function and viscoelastic mechanical behavior. One of the primary biochemical changes associated with disc degeneration is the loss of proteoglycans, which leads to tissue dehydration. While previous studies have reported the effects of in vivo degeneration on annulus fibrosus (AF) failure mechanics, the independent role of water remains unclear, as does the tissue’s rate-dependent failure response. Our first objective was to determine the effect of loading rate on AF failure properties in tension; our second objective was to quantify the effect of water content on failure properties. Water content was altered through enzymatic digestion of glycosaminoglycans (GAGs) and through osmotic loading. Bovine AF specimens were tested monotonically to failure along the circumferential direction at 0.00697%/s or 6.97%/s. Increased loading rate resulted in a ~50% increase in linear-region modulus, failure stress, and strain energy density across all treatment groups (p < 0.001). Decreased GAG and water contents resulted in decreased modulus, failure stress, and strain energy density; however, these differences were only observed at the low loading rate (p < 0.05; no changes at high rate). Osmotic loading was used to evaluate the effect of hydration independently from GAG composition, resulting in similar decreases in water content, modulus, and strain energy density. This suggests that hydration is essential for maintaining tissue stiffness and energy absorption capacity, rather than strength, and that GAGs contribute to tissue strength independently from mediating water content. |
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Keywords: | Annulus fibrosus Hydration Failure mechanics Loading rate Proteoglycan Fiber-reinforced tissue Chondroitinase Structure-function |
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