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Baldwin SJ, Sampson J, Peacock CJ, Martin ML, Veres SP, Lee JM, Kreplak L. A new longitudinal variation in the structure of collagen fibrils and its relationship to locations of mechanical damage susceptibility. J Mech Behav Biomed Mater 2020; 110:103849. [PMID: 32501220 DOI: 10.1016/j.jmbbm.2020.103849] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2019] [Revised: 03/17/2020] [Accepted: 05/04/2020] [Indexed: 11/26/2022]
Abstract
The hierarchical architecture of the collagen fibril is well understood, involving non-integer staggering of collagen molecules which results in a 67 nm periodic molecular density variation termed D-banding. Other than this variation, collagen fibrils are considered to be homogeneous at the micro-scale and beyond. Interestingly, serial kink structures have been shown to form at discrete locations along the length of collagen fibrils from some mechanically overloaded tendons. The formation of these kinks at discrete locations along the length of fibrils (discrete plasticity) may indicate pre-existing structural variations at a length scale greater than that of the D-banding. Using a high velocity nanomechanical mapping technique, 25 tendon collagen fibrils, were mechanically and structurally mapped along 10 μm of their length in dehydrated and hydrated states with resolutions of 20 nm and 8 nm respectively. Analysis of the variation in hydrated indentation modulus along individual collagen fibrils revealed a micro-scale structural variation not observed in the hydrated or dehydrated structural maps. The spacing distribution of this variation was similar to that observed for inter-kink distances seen in SEM images of discrete plasticity type damage. We propose that longitudinal variation in collagen fibril structure leads to localized mechanical susceptibility to damage under overload. Furthermore, we suggest that this variation has its origins in heterogeneous crosslink density along the length of collagen fibrils. The presence of pre-existing sites of mechanical vulnerability along the length of collagen fibrils may be important to biological remodeling of tendon, with mechanically-activated sites having distinct protein binding capabilities and enzyme susceptibility.
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Affiliation(s)
- Samuel J Baldwin
- Department of Physics and Atmospheric Science, Dalhousie University, Sir James Dunn Building, 6310 Coburg Road, Main Office Rm 218, Halifax, NS, B3H 4R2, Canada
| | - Josh Sampson
- Department of Physics and Atmospheric Science, Dalhousie University, Sir James Dunn Building, 6310 Coburg Road, Main Office Rm 218, Halifax, NS, B3H 4R2, Canada
| | - Christopher J Peacock
- Department of Physics and Atmospheric Science, Dalhousie University, Sir James Dunn Building, 6310 Coburg Road, Main Office Rm 218, Halifax, NS, B3H 4R2, Canada
| | - Meghan L Martin
- School of Biomedical Engineering, Dalhousie University, 5981 University Avenue, PO Box 15000, Halifax, NS, B3H 4R2, Canada
| | - Samuel P Veres
- School of Biomedical Engineering, Dalhousie University, 5981 University Avenue, PO Box 15000, Halifax, NS, B3H 4R2, Canada; Division of Engineering, Saint Mary's University, 923 Robie Street, Halifax, NS, B3H 3C3, Canada
| | - J Michael Lee
- School of Biomedical Engineering, Dalhousie University, 5981 University Avenue, PO Box 15000, Halifax, NS, B3H 4R2, Canada; Department of Applied Oral Sciences, Dalhousie University, 5981 University Avenue, PO Box 15000, Halifax, NS, B3H 4R2, Canada
| | - Laurent Kreplak
- Department of Physics and Atmospheric Science, Dalhousie University, Sir James Dunn Building, 6310 Coburg Road, Main Office Rm 218, Halifax, NS, B3H 4R2, Canada; School of Biomedical Engineering, Dalhousie University, 5981 University Avenue, PO Box 15000, Halifax, NS, B3H 4R2, Canada.
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Hijazi KM, Singfield KL, Veres SP. Ultrastructural response of tendon to excessive level or duration of tensile load supports that collagen fibrils are mechanically continuous. J Mech Behav Biomed Mater 2019; 97:30-40. [DOI: 10.1016/j.jmbbm.2019.05.002] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2018] [Revised: 04/24/2019] [Accepted: 05/02/2019] [Indexed: 01/12/2023]
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Baldwin SJ, Kreplak L, Lee JM. MMP-9 selectively cleaves non-D-banded material on collagen fibrils with discrete plasticity damage in mechanically-overloaded tendon. J Mech Behav Biomed Mater 2019; 95:67-75. [PMID: 30954916 DOI: 10.1016/j.jmbbm.2019.03.020] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2018] [Revised: 02/15/2019] [Accepted: 03/19/2019] [Indexed: 01/06/2023]
Abstract
The mechanical properties of tendon are due to the properties and arrangement of its collagen fibril content. Collagen fibrils are highly-organized supermolecular structures with a periodic banding pattern (D-band) indicative of the geometry of molecular organization. Following mechanical overload of whole tendon, collagen fibrils may plastically deform at discrete sites along their length, forming kinks, and acquiring a fuzzy, non-D-banded, outer layer (shell). Termed discrete plasticity, such non-uniform damage to collagen fibrils suggests localized cellular response at the fibril level during subsequent repair/replacement. Matrix metallo-proteinases (MMPs) are enzymes which act upon the extracellular matrix, facilitating cell mobility and playing important roles in wound healing. A sub-group within this family are the gelatinases, MMP-2 and MMP-9, which selectively cleave denatured collagen molecules. Of these two, MMP-9 is specifically upregulated during the initial stages of tendon repair. This suggests a singular function in damage debridement. Using atomic force microscopy (AFM), a novel fibril-level enzymatic assay was employed to assess enzymatic removal of material by trypsin and MMP-9 from individual fibrils which were: (i) untreated, (ii) partially heat denatured, (iii) or displaying discrete plasticity damaged after repeated mechanical overload. Both enzymes removed material from heat denatured and discrete plasticity-damaged fibrils; however, only MMP-9 demonstrated the selective removal of non-D-banded material, with greater removal from more damaged fibrils. The selectivity of MMP-9, coupled with documented upregulation, suggests a likely mechanism for the in vivo debridement of individual collagen fibrils, following tendon overload injury, and prior to deposition of new collagen.
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Affiliation(s)
- Samuel J Baldwin
- Department of Physics and Atmospheric Science, Dalhousie University, Sir James Dunn Building, 6310 Coburg Road, Main Office Rm 218, Halifax, NS, Canada B3H 4R2.
| | - Laurent Kreplak
- Department of Physics and Atmospheric Science, Dalhousie University, Sir James Dunn Building, 6310 Coburg Road, Main Office Rm 218, Halifax, NS, Canada B3H 4R2; School of Biomedical Engineering, Dalhousie University, 5981 University Avenue, Halifax, NS, Canada B3H 4R2
| | - J Michael Lee
- School of Biomedical Engineering, Dalhousie University, 5981 University Avenue, Halifax, NS, Canada B3H 4R2; Department of Applied Oral Sciences, Dalhousie University, 5981 University Avenue, Halifax, NS, Canada B3H 4R2.
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Baldwin SJ, Kreplak L, Lee JM. Characterization via atomic force microscopy of discrete plasticity in collagen fibrils from mechanically overloaded tendons: Nano-scale structural changes mimic rope failure. J Mech Behav Biomed Mater 2016; 60:356-366. [DOI: 10.1016/j.jmbbm.2016.02.004] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2015] [Revised: 01/22/2016] [Accepted: 02/03/2016] [Indexed: 10/22/2022]
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Nanomechanical mapping of hydrated rat tail tendon collagen I fibrils. Biophys J 2015; 107:1794-1801. [PMID: 25418160 DOI: 10.1016/j.bpj.2014.09.003] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2013] [Revised: 08/01/2014] [Accepted: 09/03/2014] [Indexed: 12/11/2022] Open
Abstract
Collagen fibrils play an important role in the human body, providing tensile strength to connective tissues. These fibrils are characterized by a banding pattern with a D-period of 67 nm. The proposed origin of the D-period is the internal staggering of tropocollagen molecules within the fibril, leading to gap and overlap regions and a corresponding periodic density fluctuation. Using an atomic force microscope high-resolution modulus maps of collagen fibril segments, up to 80 μm in length, were acquired at indentation speeds around 10(5) nm/s. The maps revealed a periodic modulation corresponding to the D-period as well as previously undocumented micrometer scale fluctuations. Further analysis revealed a 4/5, gap/overlap, ratio in the measured modulus providing further support for the quarter-staggered model of collagen fibril axial structure. The modulus values obtained at indentation speeds around 10(5) nm/s are significantly larger than those previously reported. Probing the effect of indentation speed over four decades reveals two distinct logarithmic regimes of the measured modulus and point to the existence of a characteristic molecular relaxation time around 0.1 ms. Furthermore, collagen fibrils exposed to temperatures between 50 and 62°C and cooled back to room temperature show a sharp decrease in modulus and a sharp increase in fibril diameter. This is also associated with a disappearance of the D-period and the appearance of twisted subfibrils with a pitch in the micrometer range. Based on all these data and a similar behavior observed for cross-linked polymer networks below the glass transition temperature, we propose that collagen I fibrils may be in a glassy state while hydrated.
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Veres SP, Lee JM. Designed to fail: a novel mode of collagen fibril disruption and its relevance to tissue toughness. Biophys J 2012; 102:2876-84. [PMID: 22735538 DOI: 10.1016/j.bpj.2012.05.022] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2012] [Revised: 04/13/2012] [Accepted: 05/07/2012] [Indexed: 11/16/2022] Open
Abstract
Collagen fibrils are nanostructured biological cables essential to the structural integrity of many of our tissues. Consequently, understanding the structural basis of their robust mechanical properties is of great interest. Here we present what to our knowledge is a novel mode of collagen fibril disruption that provides new insights into both the structure and mechanics of native collagen fibrils. Using enzyme probes for denatured collagen and scanning electron microscopy, we show that mechanically overloading collagen fibrils from bovine tail tendons causes them to undergo a sequential, two-stage, selective molecular failure process. Denatured collagen molecules-meaning molecules with a reduced degree of time-averaged helicity compared to those packed in undamaged fibrils-were first created within kinks that developed at discrete, repeating locations along the length of fibrils. There, collagen denaturation within the kinks was concentrated within certain subfibrils. Additional denatured molecules were then created along the surface of some disrupted fibrils. The heterogeneity of the disruption within fibrils suggests that either mechanical load is not carried equally by a fibril's subcomponents or that the subcomponents do not possess homogenous mechanical properties. Meanwhile, the creation of denatured collagen molecules, which necessarily involves the energy intensive breaking of intramolecular hydrogen bonds, provides a physical basis for the toughness of collagen fibrils.
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Affiliation(s)
- Samuel P Veres
- School of Biomedical Engineering, Dalhousie University, Halifax, Nova Scotia, Canada.
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Fessel G, Gerber C, Snedeker JG. Potential of collagen cross-linking therapies to mediate tendon mechanical properties. J Shoulder Elbow Surg 2012; 21:209-17. [PMID: 22244064 DOI: 10.1016/j.jse.2011.10.002] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/30/2011] [Accepted: 10/14/2011] [Indexed: 02/01/2023]
Abstract
Collagen cross-links are fundamental to the mechanical integrity of tendon, with orderly and progressive enzymatic cross-linking being central to healthy development and injury repair. However, the nonenzymatic cross-links that form as we age are associated with increased tendon brittleness, diminished mechanical resistance to injury, and impaired matrix remodeling. Collagen cross-linking thus sits at the center of tendon structure and function, with important implications to age, disease, injury, and therapy. The current review touches on these aspects from the perspective of their potential relevance to the shoulder surgeon. We first introduce the most well-characterized endogenous collagen cross-linkers that enable fibrillogenesis in development and healing. We also discuss the glycation-mediated cross-links that are implicated in age- and diabetes-related tendon frailty and summarize work toward therapies against these disadvantageous cross-links. Conversely, we discuss the introduction of exogenous collagen cross-links to augment the mechanical properties of collagen-based implants or native tendon tissue. We conclude with a summary of our early results using exogenous collagen cross-linkers to prevent tendon tear enlargement and eventual failure in an in vitro model of partial tendon tear.
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Affiliation(s)
- Gion Fessel
- Department of Orthopedics, University of Zurich, Zürich, Switzerland
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