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Vieira L, Mordechai HS, Sharabi M, Tipper JL, Tavakoli J. Stress relaxation behavior of the transition zone in the intervertebral disc. Acta Biomater 2024:S1742-7061(24)00547-6. [PMID: 39322045 DOI: 10.1016/j.actbio.2024.09.032] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2024] [Revised: 09/08/2024] [Accepted: 09/18/2024] [Indexed: 09/27/2024]
Abstract
The stress relaxation of the TZ region, located at the interface of the Annulus Fibrosus (AF) and Nucleus Pulposus (NP) of the disc, and how its stress is relaxed compared to the adjacent regions is unknown. The current study aimed to identify the TZ stress relaxation properties under different strain magnitudes (0.2, 0.4, and 0.6 mm/mm) and compared the TZ stress relaxation characteristics to the NP and inner AF (IAF) regions at a specific strain magnitude (0.6 mm/mm). The results of the current study revealed that the TZ region exhibited different stress relaxation properties under various strain magnitudes with significantly higher initial (p < 0.008) and reduced stresses (marginally; p = 0.06) at higher strains. Our experimental stress relaxation data revealed a significantly higher equilibrium stress for the IAF compared to the TZ and NP regions (p < 0.001) but not between the TZ and NP regions (p = 0.7). We found that NP radial stress relaxed significantly faster (p < 0.04) than the TZ and NP. Additionally, the current study proposed a simple mathematical model and identified that, consistent with experimental data, the overall effect of region on both the level of decayed stress and the rate at which stress is relaxed was significant (p < 0.006). The current study found a similar stress relaxation characteristic between the NP and TZ regions, while IAF exhibited different stress relaxation properties. It is possible that this mismatch in stress relaxation acts as a shape transformation mechanism triggered by viscoelastic behavior. STATEMENT OF SIGNIFICANCE: Our understanding of the biomechanical properties of the transition zone (TZ) in the IVD, a region at the interface of the Nucleus Pulposus (NP) and Annulus Fibrosus (AF), is sparse. Unfortunately, there are no current studies that investigate the TZ stress relaxation properties and how stress is relaxed in the TZ compared to the adjacent regions. For the first time, the current study characterized the stress relaxation properties of the TZ and described how the TZ stress is relaxed compared to its adjacent regions.
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Affiliation(s)
- Lydia Vieira
- School of Biomedical Engineering, Faculty of Engineering and Information Technology, University of Technology Sydney, NSW 2007, Australia
| | - Haim S Mordechai
- Department of Mechanical Engineering and Mechatronics, Ariel University, Ariel 407000, Israel
| | - Mirit Sharabi
- Department of Mechanical Engineering and Mechatronics, Ariel University, Ariel 407000, Israel.
| | - Joanne L Tipper
- School of Biomedical Engineering, Faculty of Engineering and Information Technology, University of Technology Sydney, NSW 2007, Australia; Department of Biomedical Engineering, School of Engineering, RMIT University, VIC 3000, Australia.
| | - Javad Tavakoli
- School of Biomedical Engineering, Faculty of Engineering and Information Technology, University of Technology Sydney, NSW 2007, Australia; Department of Biomedical Engineering, School of Engineering, RMIT University, VIC 3000, Australia.
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2
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Sun Z, Mi C. Biomechanics of annulus fibrosus: Elastic fiber simplification and degenerative impact on damage initiation and propagation. J Mech Behav Biomed Mater 2024; 157:106628. [PMID: 38878651 DOI: 10.1016/j.jmbbm.2024.106628] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2024] [Revised: 05/19/2024] [Accepted: 06/08/2024] [Indexed: 07/30/2024]
Abstract
This study addresses three primary objectives related to lumbar intervertebral disc (IVD) biomechanics under ramping quasi-static loading conditions. First, we explore the conditions justifying the simplification of axisymmetric elastic fiber families into single fiber bundles through discretized strain energy functions. Simulations reveal that a concentration factor exceeding 10 allows for a consistent deviation below 10% between simplified and non-simplified responses. Second, we investigate the impact of elastic fibers on the physiological stiffness in IVDs, revealing minimal influence on biological motions but significant effects on degeneration. Lastly, we examine the initiation and progression of annulus fibrosus (AF) damage. Our findings confirm the validity of simplifying elastic fiber families and underscore the necessity of considering elastic fiber damage in biomechanical studies of AF tissues. Elastic fibers contribute to increased biaxial stretch stiffness, and their damage significantly affects the loading capacity of the inner AF. Additionally, degeneration significantly alters the susceptibility to damage in the AF, with specific regions exhibiting higher vulnerability. Damage tends to extend circumferentially and radially, emphasizing the regional variations in collagen and elastic fiber properties. This study offers useful insights for refining biomechanical models, paving the way for a more comprehensive understanding of IVD responses and potential clinical implications.
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Affiliation(s)
- Zhongwei Sun
- Jiangsu Key Laboratory of Mechanical Analysis for Infrastructure and Advanced Equipment, School of Civil Engineering, Southeast University, Nanjing, Jiangsu 210096, China
| | - Changwen Mi
- Jiangsu Key Laboratory of Mechanical Analysis for Infrastructure and Advanced Equipment, School of Civil Engineering, Southeast University, Nanjing, Jiangsu 210096, China.
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3
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Depenveiller C, Baud S, Belloy N, Bochicchio B, Dandurand J, Dauchez M, Pepe A, Pomès R, Samouillan V, Debelle L. Structural and physical basis for the elasticity of elastin. Q Rev Biophys 2024; 57:e3. [PMID: 38501287 DOI: 10.1017/s0033583524000040] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/20/2024]
Abstract
Elastin function is to endow vertebrate tissues with elasticity so that they can adapt to local mechanical constraints. The hydrophobicity and insolubility of the mature elastin polymer have hampered studies of its molecular organisation and structure-elasticity relationships. Nevertheless, a growing number of studies from a broad range of disciplines have provided invaluable insights, and several structural models of elastin have been proposed. However, many questions remain regarding how the primary sequence of elastin (and the soluble precursor tropoelastin) governs the molecular structure, its organisation into a polymeric network, and the mechanical properties of the resulting material. The elasticity of elastin is known to be largely entropic in origin, a property that is understood to arise from both its disordered molecular structure and its hydrophobic character. Despite a high degree of hydrophobicity, elastin does not form compact, water-excluding domains and remains highly disordered. However, elastin contains both stable and labile secondary structure elements. Current models of elastin structure and function are drawn from data collected on tropoelastin and on elastin-like peptides (ELPs) but at the tissue level, elasticity is only achieved after polymerisation of the mature elastin. In tissues, the reticulation of tropoelastin chains in water defines the polymer elastin that bears elasticity. Similarly, ELPs require polymerisation to become elastic. There is considerable interest in elastin especially in the biomaterials and cosmetic fields where ELPs are widely used. This review aims to provide an up-to-date survey of/perspective on current knowledge about the interplay between elastin structure, solvation, and entropic elasticity.
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Affiliation(s)
- Camille Depenveiller
- UMR URCA/CNRS 7369, Matrice Extracellulaire et Dynamique Cellulaire (MEDyC), UFR Sciences Exactes et Naturelles, SFR CAP Santé, Université de Reims Champagne-Ardenne, Reims, France
- Unité de Génie Enzymatique et Cellulaire UMR 7025 CNRS, Université de Picardie Jules Verne, Amiens, France
| | - Stéphanie Baud
- UMR URCA/CNRS 7369, Matrice Extracellulaire et Dynamique Cellulaire (MEDyC), UFR Sciences Exactes et Naturelles, SFR CAP Santé, Université de Reims Champagne-Ardenne, Reims, France
| | - Nicolas Belloy
- UMR URCA/CNRS 7369, Matrice Extracellulaire et Dynamique Cellulaire (MEDyC), UFR Sciences Exactes et Naturelles, SFR CAP Santé, Université de Reims Champagne-Ardenne, Reims, France
| | - Brigida Bochicchio
- Laboratory of Bioinspired Materials, Department of Science, University of Basilicata, Potenza, Italy
| | - Jany Dandurand
- CIRIMAT UMR 5085, Université Paul Sabatier, Université de Toulouse, Toulouse, France
| | - Manuel Dauchez
- UMR URCA/CNRS 7369, Matrice Extracellulaire et Dynamique Cellulaire (MEDyC), UFR Sciences Exactes et Naturelles, SFR CAP Santé, Université de Reims Champagne-Ardenne, Reims, France
| | - Antonietta Pepe
- Laboratory of Bioinspired Materials, Department of Science, University of Basilicata, Potenza, Italy
| | - Régis Pomès
- Molecular Medicine, Hospital for Sick Children, Toronto, ON, Canada
- Department of Biochemistry, University of Toronto, Toronto, ON, Canada
| | - Valérie Samouillan
- CIRIMAT UMR 5085, Université Paul Sabatier, Université de Toulouse, Toulouse, France
| | - Laurent Debelle
- UMR URCA/CNRS 7369, Matrice Extracellulaire et Dynamique Cellulaire (MEDyC), UFR Sciences Exactes et Naturelles, SFR CAP Santé, Université de Reims Champagne-Ardenne, Reims, France
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Sun Z, Sun Y, Mi C. Comprehensive modeling of annulus fibrosus: From biphasic refined characterization to damage accumulation under viscous loading. Acta Biomater 2024; 174:228-244. [PMID: 38070844 DOI: 10.1016/j.actbio.2023.12.007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2023] [Revised: 11/26/2023] [Accepted: 12/05/2023] [Indexed: 12/17/2023]
Abstract
The annulus fibrosus (AF), a permeable, hydrated, and fiber-reinforced soft tissue, exhibits complex responses influenced by fluid pressure, osmotic pressure, and structural mechanics. Existing models struggle to comprehensively represent these intricate interactions and the heterogeneous solid responses within the AF. Additionally, the mechanisms driving differential damage accumulation between non-degenerative and degenerative intervertebral discs remain poorly understood. In this study, we introduce a biphasic-swelling damage model for the AF. We conceptually develop and rigorously validate this model through tissue-level tests employing various loading modes, consistently aligning model predictions with experimental data. Leveraging parametric geometric algorithms and custom Python scripts, we construct models simulating both non-degenerative and degenerative discs. Following calibration, we subject these models to viscous loading protocols. Our findings reveal the posterior AF's susceptibility to damage, contingent upon loading rate and water content. We elucidate the underlying mechanisms by examining the temporal evolution of fluid pressure, osmotic pressure, and the regionally dependent fiber network. This research presents a highly accurate model of the AF, providing valuable insights into disc damage. Future research endeavors should expand this model to incorporate ionic transport and diffusion, enabling a more profound exploration of intervertebral disc mechanobiology. This comprehensive model contributes to a better understanding of AF behavior and may inform therapeutic strategies for disc-related pathologies. STATEMENT OF SIGNIFICANCE: This research presents a comprehensive model of the annulus fibrosus (AF), a crucial component of the intervertebral disc that provides structural support and resists deformation. The study introduces a biphasic-swelling damage model for the AF and validates it through tissue-level tests. The model accounts for fluid pressure, osmotic pressure, and matrix mechanics, providing a more accurate representation of the AF's behavior. The study also investigates the differential damage accumulation between non-degenerative and degenerative discs, shedding light on the mechanisms driving disc degeneration. The findings have significant implications for medical treatments and interventions, as they highlight the posterior AF's susceptibility to damage. This research is of great interest to readers interested in biomechanics, tissue engineering, and medical treatments for disc degeneration.
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Affiliation(s)
- Zhongwei Sun
- Jiangsu Key Laboratory of Engineering Mechanics, School of Civil Engineering, Southeast University, Nanjing, Jiangsu 210096, China
| | - Yueli Sun
- Longhua Hospital, Shanghai University of Traditional Chinese Medicine, Shanghai, Shanghai 200032, China
| | - Changwen Mi
- Jiangsu Key Laboratory of Engineering Mechanics, School of Civil Engineering, Southeast University, Nanjing, Jiangsu 210096, China.
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Su Z, Tan P, Zhang J, Wang P, Zhu S, Jiang N. Understanding the Mechanics of the Temporomandibular Joint Osteochondral Interface from Micro- and Nanoscopic Perspectives. NANO LETTERS 2023; 23:11702-11709. [PMID: 38060440 DOI: 10.1021/acs.nanolett.3c03564] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2023]
Abstract
The condylar cartilage of the temporomandibular joint (TMJ) is connected to the subchondral bone by an osteochondral interface that transmits loads without causing fatigue damage. However, the microstructure, composition, and mechanical properties of this interface remain elusive. In this study, we found that structurally, a spatial gradient assembly of hydroxyapatite (HAP) particles exists in the osteochondral interface, with increasing volume of apatite crystals with depth and a tendency to form denser and stacked structures. Combined with nanoindentation, this complex assembly of nanoscale structures and components enhanced energy dissipation at the osteochondral interface, achieving a smooth stress transition between soft and hard tissues. This study comprehensively demonstrates the elemental composition and complex nanogradient spatial assembly of the osteochondral interface at the ultramicroscopic scale, providing a basis for exploring the construction of complex mechanical models of the interfacial region.
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Affiliation(s)
- Zhan Su
- State Key Laboratory of Oral Diseases & National Center for Stomatology & National Clinical Research Center for Oral Diseases & Department of Orthognathic and TMJ Surgery, West China Hospital of Stomatology, Sichuan University, Chengdu 610041, Sichuan, China
| | - Peijie Tan
- State Key Laboratory of Oral Diseases & National Center for Stomatology & National Clinical Research Center for Oral Diseases & Department of Orthognathic and TMJ Surgery, West China Hospital of Stomatology, Sichuan University, Chengdu 610041, Sichuan, China
| | - Jie Zhang
- State Key Laboratory of Oral Diseases & National Center for Stomatology & National Clinical Research Center for Oral Diseases & Department of Orthognathic and TMJ Surgery, West China Hospital of Stomatology, Sichuan University, Chengdu 610041, Sichuan, China
| | - Peng Wang
- State Key Laboratory of Oral Diseases & National Center for Stomatology & National Clinical Research Center for Oral Diseases & Department of Orthognathic and TMJ Surgery, West China Hospital of Stomatology, Sichuan University, Chengdu 610041, Sichuan, China
| | - Songsong Zhu
- State Key Laboratory of Oral Diseases & National Center for Stomatology & National Clinical Research Center for Oral Diseases & Department of Orthognathic and TMJ Surgery, West China Hospital of Stomatology, Sichuan University, Chengdu 610041, Sichuan, China
| | - Nan Jiang
- State Key Laboratory of Oral Diseases & National Center for Stomatology & National Clinical Research Center for Oral Diseases & Department of Orthognathic and TMJ Surgery, West China Hospital of Stomatology, Sichuan University, Chengdu 610041, Sichuan, China
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Tavakoli J, Diwan AD, Tipper JL. Intervertebral disc-on-a-chip: a precision engineered toolbox for low back pain studies. Trends Biotechnol 2023; 41:1339-1342. [PMID: 37188576 DOI: 10.1016/j.tibtech.2023.04.009] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2023] [Revised: 04/24/2023] [Accepted: 04/24/2023] [Indexed: 05/17/2023]
Abstract
Current in vitro intervertebral disc (IVD) models do not fully recapitulate the complex mechanobiology of native tissue, and so far there is no strategy to effectively evaluate IVD regeneration. The development of a modular microfluidic on-chip model is expected to enhance the physiological relevance of experimental data leading to successful clinical outcomes.
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Affiliation(s)
- Javad Tavakoli
- School of Biomedical Engineering, University of Technology Sydney, Sydney, NSW, Australia; SpineLabs, St George and Sutherland Clinical School, University of New South Wales, Sydney, NSW, Australia.
| | - Ashish D Diwan
- SpineLabs, St George and Sutherland Clinical School, University of New South Wales, Sydney, NSW, Australia; Spine Service, Department of Orthopaedic Surgery, St George Hospital Campus, Kogarah, NSW, Australia
| | - Joanne L Tipper
- School of Biomedical Engineering, University of Technology Sydney, Sydney, NSW, Australia; Institute of Medical and Biological Engineering, School of Mechanical Engineering, University of Leeds, Leeds, UK.
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7
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Sun Z, Mi C. On the identification of the ultra-structural organization of elastic fibers and their effects on the integrity of annulus fibrosus. J Biomech 2023; 157:111728. [PMID: 37499432 DOI: 10.1016/j.jbiomech.2023.111728] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2023] [Revised: 07/10/2023] [Accepted: 07/14/2023] [Indexed: 07/29/2023]
Abstract
Due to the complicated structure of the elastic fiber network in annulus fibrosus, existing in-silico studies either simplified or just overlooked its distribution pattern. Nonetheless, experimental and simulation results have proven that elastic fibers are of great importance to maintaining the structural integrity of annulus fibrosus and therefore to ensuring the load-bearing ability of intervertebral discs. Such needs call for a fine model. This work aims at developing a biphasic annulus fibrosus model by incorporating the accurate distribution pattern of collagen and elastic fibers. Both the structural parameters and intrinsic mechanical parameters were successfully identified using single lamella and inter-lamella microscopy anatomy and micromechanical testing data. The proposed model was then used to implement finite element simulations on various anterior and posterolateral multi-lamellae annulus fibrosus specimens. In general, simulation results agree well with available experimental and simulation data. On this basis, the effects of elastic fibers on the integrity of annulus fibrosus were further investigated. It was found that elastic fibers significantly influence the free swelling, radial stretching and circumferential shear performances of annulus fibrosus. Nonetheless, no significant effects were found for the circumferential stretching capability. The proposed biphasic model considers for the first time the distribution characteristics of elastic fibers at two scales, including both the principal orientations of all fiber families and the detailed distribution pattern within each family. Better understandings on the functions of collagen and elastic fibers can therefore be realized. To further enhance its prediction capability, the current model can be extended in the future by taking the fiber-matrix interaction as well as progressive damages into consideration.
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Affiliation(s)
- Zhongwei Sun
- Jiangsu Key Laboratory of Engineering Mechanics, School of Civil Engineering, Southeast University, Nanjing, Jiangsu 210096, China
| | - Changwen Mi
- Jiangsu Key Laboratory of Engineering Mechanics, School of Civil Engineering, Southeast University, Nanjing, Jiangsu 210096, China.
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8
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Mordechai HS, Aharonov A, Sharon SE, Bonshtein I, Simon C, Sivan SS, Sharabi M. Toward a mechanically biocompatible intervertebral disc: Engineering of combined biomimetic annulus fibrosus and nucleus pulposus analogs. J Biomed Mater Res A 2023; 111:618-633. [PMID: 36815687 DOI: 10.1002/jbm.a.37519] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2022] [Revised: 02/09/2023] [Accepted: 02/11/2023] [Indexed: 02/24/2023]
Abstract
Intervertebral disc (IVD) degeneration and accompanying lower back pain impose global medical and societal challenges, affecting over 600 million people worldwide. The IVD complex fibrocartilaginous structure is responsible for the spine biomechanical function. The nucleus pulposus (NP), composed of swellable glycosaminoglycan (GAG), transfers compressive loads to the surrounding fiber-reinforced annulus fibrosus (AF) lamellae, which stretches under tension. Together, these substructures allow the IVD to withstand extremely high and complex loads. Key to mimic the complete disc must consider the properties of its substructures. This study presents three novel substructures-a biomimetic silk-reinforced composite lamella for the AF, a GAG analog for the NP, and a novel biomimetic combined AF-NP construct. The biomimetic AF demonstrates nonlinear, hyperelastic, and anisotropic behavior similar to the native human AF, while the NP analog demonstrates mechanical behavior similar to the human NP. The synergized biomimetic AF-NP demonstrates similar behavior to the unconfined NP, with significantly increased deformations indicating improved performance. Validation of the AF-NP construct mechanics using a finite element model yields results compatible with native human IVD under various physiological loadings. The ability of our AF-NP construct to mimic the native IVD offers a revolutionary concept for the potential development of a fully functional IVD.
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Affiliation(s)
- Haim S Mordechai
- Department of Mechanical Engineering & Mechatronics, Ariel University, Ariel, Israel
| | - Adi Aharonov
- Department of Mechanical Engineering & Mechatronics, Ariel University, Ariel, Israel
| | - Smadar E Sharon
- Department of Mechanical Engineering & Mechatronics, Ariel University, Ariel, Israel
| | - Iris Bonshtein
- Department of Biotechnology Engineering, Braude College of Engineering, Karmiel, Israel
| | - Chen Simon
- Department of Biotechnology Engineering, Braude College of Engineering, Karmiel, Israel
| | - Sarit S Sivan
- Department of Biotechnology Engineering, Braude College of Engineering, Karmiel, Israel
| | - Mirit Sharabi
- Department of Mechanical Engineering & Mechatronics, Ariel University, Ariel, Israel
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Structure-function characterization of the transition zone in the intervertebral disc. Acta Biomater 2023; 160:164-175. [PMID: 36804822 DOI: 10.1016/j.actbio.2023.02.019] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2022] [Revised: 02/05/2023] [Accepted: 02/09/2023] [Indexed: 02/17/2023]
Abstract
Understanding the structure-function relationship in the intervertebral disk (IVD) is crucial for the development of novel tissue engineering strategies to regenerate IVD and the establishment of accurate computational models for low back pain research. A large number of studies have improved our knowledge of the mechanical and structural properties of the nucleus pulposus (NP) and annulus fibrosus (AF), two of the main regions in the IVD. However, few studies have focused on the AF-NP interface (transition zone; TZ). Therefore, the current study aims to, for the first time, characterize the cyclic and failure mechanical properties of the TZ region under physiological loading (1, 3, and 5%s-1 strain rates) and investigate the structural integration mechanisms between the NP, TZ, and AF regions. The results of the current study reveal significant effects of region (NP, TZ, and AF) and strain rates (1, 3, and 5%s-1) on stiffness (p < 0.001). In addition, energy absorption is significantly higher for the AF compared to the TZ and NP (p <0.001) as well as between the TZ and NP (p <0.001). The current research finds adaptation, direct penetration, and entanglement between TZ and AF fibers as three common mechanisms for structural integration between the TZ and AF regions. STATEMENT OF SIGNIFICANCE: Despite a large number of studies that have mechanically, structurally, and biologically characterized the nucleus pulposus (NP) and annulus fibrosus (AF) regions, few studies have focused on the NP-AF interface region (known as Transition Zone; TZ) in the IVD; hence, our understanding of the TZ structure-function relationship is still incomplete. Of particular importance, the cyclic mechanical properties of the TZ, compared to the adjacent regions (NP and AF), are yet to be explored and the precise nature of the structural integration between the NP and AF via the TZ region is not yet known. The current study explores both the mechanical and structural properties of the TZ region to ultimately identify the mechanism of integration between the NP and AF.
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Cyril D, Giugni A, Bangar SS, Mirzaeipoueinak M, Shrivastav D, Sharabi M, Tipper JL, Tavakoli J. Elastic Fibers in the Intervertebral Disc: From Form to Function and toward Regeneration. Int J Mol Sci 2022; 23:8931. [PMID: 36012198 PMCID: PMC9408956 DOI: 10.3390/ijms23168931] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2022] [Revised: 08/05/2022] [Accepted: 08/08/2022] [Indexed: 11/16/2022] Open
Abstract
Despite extensive efforts over the past 40 years, there is still a significant gap in knowledge of the characteristics of elastic fibers in the intervertebral disc (IVD). More studies are required to clarify the potential contribution of elastic fibers to the IVD (healthy and diseased) function and recommend critical areas for future investigations. On the other hand, current IVD in-vitro models are not true reflections of the complex biological IVD tissue and the role of elastic fibers has often been ignored in developing relevant tissue-engineered scaffolds and realistic computational models. This has affected the progress of IVD studies (tissue engineering solutions, biomechanics, fundamental biology) and translation into clinical practice. Motivated by the current gap, the current review paper presents a comprehensive study (from the early 1980s to 2022) that explores the current understanding of structural (multi-scale hierarchy), biological (development and aging, elastin content, and cell-fiber interaction), and biomechanical properties of the IVD elastic fibers, and provides new insights into future investigations in this domain.
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Affiliation(s)
- Divya Cyril
- Centre for Health Technologies, School of Biomedical Engineering, Faculty of Engineering and Information Technology, University of Technology Sydney, Sydney, NSW 2007, Australia
| | - Amelia Giugni
- Centre for Health Technologies, School of Biomedical Engineering, Faculty of Engineering and Information Technology, University of Technology Sydney, Sydney, NSW 2007, Australia
| | - Saie Sunil Bangar
- Faculty of Science, University of Technology Sydney, Sydney, NSW 2007, Australia
| | - Melika Mirzaeipoueinak
- Centre for Health Technologies, School of Biomedical Engineering, Faculty of Engineering and Information Technology, University of Technology Sydney, Sydney, NSW 2007, Australia
| | - Dipika Shrivastav
- Centre for Health Technologies, School of Biomedical Engineering, Faculty of Engineering and Information Technology, University of Technology Sydney, Sydney, NSW 2007, Australia
| | - Mirit Sharabi
- Department of Mechanical Engineering and Mechatronics, Ariel University, Ariel 407000, Israel
| | - Joanne L. Tipper
- Centre for Health Technologies, School of Biomedical Engineering, Faculty of Engineering and Information Technology, University of Technology Sydney, Sydney, NSW 2007, Australia
| | - Javad Tavakoli
- Centre for Health Technologies, School of Biomedical Engineering, Faculty of Engineering and Information Technology, University of Technology Sydney, Sydney, NSW 2007, Australia
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Tavakoli J, Tipper JL. Detailed mechanical characterization of the transition zone: New insight into the integration between the annulus and nucleus of the intervertebral disc. Acta Biomater 2022; 143:87-99. [PMID: 35259517 DOI: 10.1016/j.actbio.2022.03.002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2021] [Revised: 02/27/2022] [Accepted: 03/01/2022] [Indexed: 11/19/2022]
Abstract
The Nucleus Pulposus (NP) and Annulus Fibrous (AF) are two primary regions of the intervertebral disc (IVD). The interface between the AF and NP, where the gradual transition in structure and type of fibers are observed, is known as the Transition Zone (TZ). Recent structural studies have shown that the TZ contains organized fibers that appear to connect the NP to the AF. However, the mechanical characteristics of the TZ are yet to be explored. The current study aimed to investigate the mechanical properties of the TZ at the anterolateral (AL) and posterolateral (PL) regions in both radial and circumferential directions of loading using ovine IVDs (N = 28). Young's and toe moduli, maximum stress, failure strain, strain at maximum stress, and toughness were calculated mechanical parameters. The findings from this study revealed that the mechanical properties of the TZ, including young's modulus (p = 0.001), failure strain (p < 0.001), strain at maximum stress (p = 0.002), toughness (p = 0.027), and toe modulus (p = 0.005), were significantly lower for the PL compared to the AL region. Maximum stress was not significantly different between the PL and AL regions (p = 0.164). We found that maximum stress (p = 0.002), failure strain (p < 0.001), and toughness (p = 0.001) were significantly different in different loading directions. No significant differences for modulus (young's; p = 0.169 and toe; p = 0.352) and strain at maximum stress (p = 0.727) were found between the radial and circumferential loading directions. STATEMENT OF SIGNIFICANCE: To date there has not been a study that has investigated the mechanical characterization of the annulus (AF)-nucleus (NP) interface (transition zone; TZ) in the intervertebral disc (IVD), nor is it known whether the posterolateral (PL) and anterolateral (AL) regions of the TZ exhibit different mechanical properties. Accordingly, the TZ mechanical properties have been rarely used in the development of computational IVD models and relevant tissue-engineered scaffolds. The current research reported the mechanical properties of the TZ region and revealed that its mechanical properties were significantly lower for the PL compared to the AL region. These new findings enhance our knowledge about the nature of AF-NP integration and may help to develop more realistic tissue-engineered or computational IVD models.
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Affiliation(s)
- Javad Tavakoli
- Centre for Health Technologies, Faculty of Engineering and Information Technology, School of Biomedical Engineering, University of Technology Sydney, NSW, Australia.
| | - Joanne L Tipper
- Centre for Health Technologies, Faculty of Engineering and Information Technology, School of Biomedical Engineering, University of Technology Sydney, NSW, Australia.
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Tavakoli J, Geargeflia S, Tipper JL, Diwan AD. Magnetic resonance elastography: A non-invasive biomarker for low back pain studies. BIOMEDICAL ENGINEERING ADVANCES 2021. [DOI: 10.1016/j.bea.2021.100014] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022] Open
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Modeling multiaxial damage regional variation in human annulus fibrosus. Acta Biomater 2021; 136:375-388. [PMID: 34547514 DOI: 10.1016/j.actbio.2021.09.017] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2021] [Revised: 09/08/2021] [Accepted: 09/13/2021] [Indexed: 01/03/2023]
Abstract
In the present article, a fully three-dimensional human annulus fibrosus model is developed by considering the regional variation of the complex structural organization of collagen network at different scales to predict the regional anisotropic multiaxial damage of the intervertebral disc. The model parameters are identified using experimental data considering as elementary structural unit, the single annulus lamellae stretched till failure along the micro-sized collagen fibers. The multi-layered lamellar/inter-lamellar annulus model is constructed by considering the effective interactions between adjacent layers and the chemical-induced volumetric strain. The regional dependent model predictions are analyzed under various loading modes and compared to experimental data when available. The stretching along the circumferential and radial directions till failure serves to check the predictive capacities of the annulus model. Model results under simple shear, biaxial stretching and plane-strain compression are further presented and discussed. Finally, a full disc model is constructed using the regional annulus model and simulations are presented to assess the most likely failed areas under disc axial compression. STATEMENT OF SIGNIFICANCE: The damage in annulus soft tissues is a complex multiscale phenomenon due to a complex structural arrangement of collagen network at different scales of hierarchical organization. A fully three-dimensional constitutive representation that considers the regional variation of the structural complexity to estimate annulus multiaxial mechanics till failure has not yet been developed. Here, a model is developed to predict deformation-induced damage and failure of annulus under multiaxial loading histories considering as time-dependent physical process both chemical-induced volumetric effects and damage accumulation. After model identification using single lamellae extracted from different disc regions, the model predictability is verified for various multiaxial elementary loading modes representative of the spine movement. The heterogeneous mechanics of a full human disc model is finally presented.
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