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Raymond-Hayling H, Lu Y, Kadler KE, Shearer T. A fibre tracking algorithm for volumetric microstructural data - application to tendons. Acta Biomater 2022. [DOI: 10.1016/j.actbio.2022.10.043] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022]
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2
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Eisner LE, Rosario R, Andarawis-Puri N, Arruda EM. The Role of the Non-Collagenous Extracellular Matrix in Tendon and Ligament Mechanical Behavior: A Review. J Biomech Eng 2022; 144:1128818. [PMID: 34802057 PMCID: PMC8719050 DOI: 10.1115/1.4053086] [Citation(s) in RCA: 14] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2021] [Indexed: 12/26/2022]
Abstract
Tendon is a connective tissue that transmits loads from muscle to bone, while ligament is a similar tissue that stabilizes joint articulation by connecting bone to bone. The 70-90% of tendon and ligament's extracellular matrix (ECM) is composed of a hierarchical collagen structure that provides resistance to deformation primarily in the fiber direction, and the remaining fraction consists of a variety of non-collagenous proteins, proteoglycans, and glycosaminoglycans (GAGs) whose mechanical roles are not well characterized. ECM constituents such as elastin, the proteoglycans decorin, biglycan, lumican, fibromodulin, lubricin, and aggrecan and their associated GAGs, and cartilage oligomeric matrix protein (COMP) have been suggested to contribute to tendon and ligament's characteristic quasi-static and viscoelastic mechanical behavior in tension, shear, and compression. The purpose of this review is to summarize existing literature regarding the contribution of the non-collagenous ECM to tendon and ligament mechanics, and to highlight key gaps in knowledge that future studies may address. Using insights from theoretical mechanics and biology, we discuss the role of the non-collagenous ECM in quasi-static and viscoelastic tensile, compressive, and shear behavior in the fiber direction and orthogonal to the fiber direction. We also address the efficacy of tools that are commonly used to assess these relationships, including enzymatic degradation, mouse knockout models, and computational models. Further work in this field will foster a better understanding of tendon and ligament damage and healing as well as inform strategies for tissue repair and regeneration.
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Affiliation(s)
- Lainie E Eisner
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI 48109; Meinig School of Biomedical Engineering, Cornell University, Ithaca, NY 14853
| | - Ryan Rosario
- Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI 48109
| | - Nelly Andarawis-Puri
- Sibley School of Mechanical and Aerospace Engineering, Cornell University, Ithaca, NY 14853
| | - Ellen M Arruda
- Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI 48109; Professor Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI 48109; Professor Program in Macromolecular Science and Engineering, University of Michigan, Ann Arbor, MI 48109
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Revell CK, Jensen OE, Shearer T, Lu Y, Holmes DF, Kadler KE. Collagen fibril assembly: New approaches to unanswered questions. Matrix Biol Plus 2021; 12:100079. [PMID: 34381990 PMCID: PMC8334717 DOI: 10.1016/j.mbplus.2021.100079] [Citation(s) in RCA: 25] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2021] [Revised: 06/27/2021] [Accepted: 06/28/2021] [Indexed: 12/22/2022] Open
Abstract
Collagen fibrils are essential for metazoan life. They are the largest, most abundant, and most versatile protein polymers in animals, where they occur in the extracellular matrix to form the structural basis of tissues and organs. Collagen fibrils were first observed at the turn of the 20th century. During the last 40 years, the genes that encode the family of collagens have been identified, the structure of the collagen triple helix has been solved, the many enzymes involved in the post-translational modifications of collagens have been identified, mutations in the genes encoding collagen and collagen-associated proteins have been linked to heritable disorders, and changes in collagen levels have been associated with a wide range of diseases, including cancer. Yet despite extensive research, a full understanding of how cells assemble collagen fibrils remains elusive. Here, we review current models of collagen fibril self-assembly, and how cells might exert control over the self-assembly process to define the number, length and organisation of fibrils in tissues.
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Affiliation(s)
- Christopher K. Revell
- Department of Mathematics, University of Manchester, Alan Turing Building, Oxford Road, Manchester M13 9PL, UK
- Wellcome Centre for Cell-Matrix Research, Faculty of Biology, Medicine and Health, University of Manchester, Michael Smith Building, Oxford Road, Manchester M13 9PT, UK
| | - Oliver E. Jensen
- Department of Mathematics, University of Manchester, Alan Turing Building, Oxford Road, Manchester M13 9PL, UK
- Wellcome Centre for Cell-Matrix Research, Faculty of Biology, Medicine and Health, University of Manchester, Michael Smith Building, Oxford Road, Manchester M13 9PT, UK
| | - Tom Shearer
- Department of Mathematics, University of Manchester, Alan Turing Building, Oxford Road, Manchester M13 9PL, UK
- Department of Materials, University of Manchester, Oxford Road, Manchester M13 9PL, UK
| | - Yinhui Lu
- Wellcome Centre for Cell-Matrix Research, Faculty of Biology, Medicine and Health, University of Manchester, Michael Smith Building, Oxford Road, Manchester M13 9PT, UK
| | - David F. Holmes
- Wellcome Centre for Cell-Matrix Research, Faculty of Biology, Medicine and Health, University of Manchester, Michael Smith Building, Oxford Road, Manchester M13 9PT, UK
| | - Karl E. Kadler
- Wellcome Centre for Cell-Matrix Research, Faculty of Biology, Medicine and Health, University of Manchester, Michael Smith Building, Oxford Road, Manchester M13 9PT, UK
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4
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Tracking tendon fibers to their insertion - a 3D analysis of the Achilles tendon enthesis in mice. Acta Biomater 2021; 120:146-155. [PMID: 32428686 DOI: 10.1016/j.actbio.2020.05.001] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2020] [Revised: 04/16/2020] [Accepted: 05/01/2020] [Indexed: 11/23/2022]
Abstract
Tendon insertions to bone are heavily loaded transitions between soft and hard tissues. The fiber courses in the tendon have profound effects on the distribution of stress along and across the insertion. We tracked fibers of the Achilles tendon in mice in micro-computed tomographies and extracted virtual transversal sections. The fiber tracks and shapes were analyzed from a position in the free tendon to the insertion. Mechanically relevant parameters were extracted. The fiber number was found to stay about constant along the tendon. But the fiber cross-sectional areas decrease towards the insertion. The fibers mainly interact due to tendon twist, while branching only creates small branching clusters with low levels of divergence along the tendon. The highest fiber curvatures were found within the unmineralized entheseal fibrocartilage. The fibers inserting at a protrusion of the insertion area form a distinct portion within the tendon. Tendon twist is expected to contribute to a homogeneous distribution of stress among the fibers. According to the low cross-sectional areas and the high fiber curvatures, tensile and compressive stress are expected to peak at the insertion. These findings raise the question whether the insertion is reinforced in terms of fiber strength or by other load-bearing components besides the fibers. STATEMENT OF SIGNIFICANCE: The presented study is the first analysis of the 3D fiber tracks in macroscopic tendon samples as determined by a combination of cell-maceration, phase-contrast µCT and template-based tracking. The structural findings change the understanding of the tendon-bone insertion and its biomechanics: (1) The insertion is not reinforced in terms of fiber numbers or sizes. Its robustness remains unexplained. (2) The orientation of fibers in the tendon center is higher than in the margins. This arrangement could inspire material development. (3) Fibers inserting at a protrusion of the insertion area stem from a distinct portion within the tendon. The results show that fibrous structure analysis can link macro- to micromechanics and that it is ready for the application to complete muscle-tendon units.
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Müller WE, Schröder HC, Wang X. Inorganic Polyphosphates As Storage for and Generator of Metabolic Energy in the Extracellular Matrix. Chem Rev 2019; 119:12337-12374. [PMID: 31738523 PMCID: PMC6935868 DOI: 10.1021/acs.chemrev.9b00460] [Citation(s) in RCA: 91] [Impact Index Per Article: 18.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2019] [Indexed: 12/14/2022]
Abstract
Inorganic polyphosphates (polyP) consist of linear chains of orthophosphate residues, linked by high-energy phosphoanhydride bonds. They are evolutionarily old biopolymers that are present from bacteria to man. No other molecule concentrates as much (bio)chemically usable energy as polyP. However, the function and metabolism of this long-neglected polymer are scarcely known, especially in higher eukaryotes. In recent years, interest in polyP experienced a renaissance, beginning with the discovery of polyP as phosphate source in bone mineralization. Later, two discoveries placed polyP into the focus of regenerative medicine applications. First, polyP shows morphogenetic activity, i.e., induces cell differentiation via gene induction, and, second, acts as an energy storage and donor in the extracellular space. Studies on acidocalcisomes and mitochondria provided first insights into the enzymatic basis of eukaryotic polyP formation. In addition, a concerted action of alkaline phosphatase and adenylate kinase proved crucial for ADP/ATP generation from polyP. PolyP added extracellularly to mammalian cells resulted in a 3-fold increase of ATP. The importance and mechanism of this phosphotransfer reaction for energy-consuming processes in the extracellular matrix are discussed. This review aims to give a critical overview about the formation and function of this unique polymer that is capable of storing (bio)chemically useful energy.
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Affiliation(s)
- Werner E.G. Müller
- ERC Advanced Investigator
Grant Research
Group at the Institute for Physiological Chemistry, University Medical Center of the Johannes Gutenberg University, Duesbergweg 6, D-55128 Mainz, Germany
| | - Heinz C. Schröder
- ERC Advanced Investigator
Grant Research
Group at the Institute for Physiological Chemistry, University Medical Center of the Johannes Gutenberg University, Duesbergweg 6, D-55128 Mainz, Germany
| | - Xiaohong Wang
- ERC Advanced Investigator
Grant Research
Group at the Institute for Physiological Chemistry, University Medical Center of the Johannes Gutenberg University, Duesbergweg 6, D-55128 Mainz, Germany
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Szczesny SE, Fetchko KL, Dodge GR, Elliott DM. Evidence that interfibrillar load transfer in tendon is supported by small diameter fibrils and not extrafibrillar tissue components. J Orthop Res 2017; 35:2127-2134. [PMID: 28071819 PMCID: PMC5503823 DOI: 10.1002/jor.23517] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/26/2016] [Accepted: 01/06/2017] [Indexed: 02/06/2023]
Abstract
Collagen fibrils in tendon are believed to be discontinuous and transfer tensile loads through shear forces generated during interfibrillar sliding. However, the structures that transmit these interfibrillar forces are unknown. Various extrafibrillar tissue components (e.g., glycosaminoglycans, collagens XII and XIV) have been suggested to transmit interfibrillar loads by bridging collagen fibrils. Alternatively, collagen fibrils may interact directly through physical fusions and interfibrillar branching. The objective of this study was to test whether extrafibrillar proteins are necessary to transmit load between collagen fibrils or if interfibrillar load transfer is accomplished directly by the fibrils themselves. Trypsin digestions were used to remove a broad spectrum of extrafibrillar proteins and measure their contribution to the multiscale mechanics of rat tail tendon fascicles. Additionally, images obtained from serial block-face scanning electron microscopy were used to determine the three-dimensional fibrillar organization in tendon fascicles and identify any potential interfibrillar interactions. While trypsin successfully removed several extrafibrillar tissue components, there was no change in the macroscale fascicle mechanics or fibril:tissue strain ratio. Furthermore, the imaging data suggested that a network of smaller diameter fibrils (<150 nm) wind around and fuse with their neighboring larger diameter fibrils. These findings demonstrate that interfibrillar load transfer is not supported by extrafibrillar tissue components and support the hypothesis that collagen fibrils are capable of transmitting loads themselves. Conclusively determining how fibrils bear load within tendon is critical for identifying the mechanisms that impair tissue function with degeneration and for restoring tissue properties via cell-mediated regeneration or engineered tissue replacements. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2127-2134, 2017.
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Affiliation(s)
- Spencer E. Szczesny
- Department of Bioengineering, University of Pennsylvania, 240 Skirkanich Hall, 210 South 33rd St, Philadelphia, PA 19104
| | - Kristen L. Fetchko
- Department of Biomedical Engineering, University of Delaware, 161 Colburn Lab, 150 Academy Street, Newark, DE 19716
| | - George R. Dodge
- Department of Orthopaedic Surgery, University of Pennsylvania, 424 Stemmler Hall, 36 St & Hamilton Walk, Philadelphia, PA 19104,Translational Musculoskeletal Research Center, Corporal Michael J. Crescenz Veterans Affairs Medical Center, 3900 Woodland Ave, Philadelphia, PA 19104
| | - Dawn M. Elliott
- Department of Biomedical Engineering, University of Delaware, 161 Colburn Lab, 150 Academy Street, Newark, DE 19716,Corresponding Author: Dawn M. Elliott, Ph.D., 161 Colburn Lab, 150 Academy Street, Newark, DE 19716, Phone: 302-831-1295,
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7
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Lee AH, Szczesny SE, Santare MH, Elliott DM. Investigating mechanisms of tendon damage by measuring multi-scale recovery following tensile loading. Acta Biomater 2017; 57:363-372. [PMID: 28435080 PMCID: PMC6688648 DOI: 10.1016/j.actbio.2017.04.011] [Citation(s) in RCA: 37] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2016] [Revised: 04/07/2017] [Accepted: 04/11/2017] [Indexed: 01/28/2023]
Abstract
Tendon pathology is associated with damage. While tendon damage is likely initiated by mechanical loading, little is known about the specific etiology. Damage is defined as an irreversible change in the microstructure that alters the macroscopic mechanical parameters. In tendon, the link between mechanical loading and microstructural damage, resulting in macroscopic changes, is not fully elucidated. In addition, tendon damage at the macroscale has been proposed to initiate when tendon is loaded beyond a strain threshold, yet the metrics to define the damage threshold are not determined. We conducted multi-scale mechanical testing to investigate the mechanism of tendon damage by simultaneously quantifying macroscale mechanical and microstructural changes. At the microscale, we observe full recovery of the fibril strain and only partial recovery of the interfibrillar sliding, indicating that the damage initiates at the interfibrillar structures. We show that non-recoverable sliding is a mechanism for tendon damage and is responsible for the macroscale decreased linear modulus and elongated toe-region observed at the fascicle-level, and these macroscale properties are appropriate metrics that reflect tendon damage. We concluded that the inflection point of the stress-strain curve represents the damage threshold and, therefore, may be a useful parameter for future studies. Establishing the mechanism of damage at multiple length scales can improve prevention and rehabilitation strategies for tendon pathology. STATEMENT OF SIGNIFICANCE Tendon pathology is associated with mechanically induced damage. Damage, as defined in engineering, is an irreversible change in microstructure that alters the macroscopic mechanical properties. Although microstructural damage and changes to macroscale mechanics are likely, this link to microstructural change was not yet established. We conducted multiscale mechanical testing to investigate the mechanism of tendon damage by simultaneously quantifying macroscale mechanical and microstructural changes. We showed that non-recoverable sliding between collagen fibrils is a mechanism for tendon damage. Establishing the mechanism of damage at multiple length scales can improve prevention and rehabilitation strategies for tendon pathology.
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Affiliation(s)
- Andrea H Lee
- Department of Biomedical Engineering, University of Delaware, United States
| | - Spencer E Szczesny
- Department of Orthopaedic Surgery, University of Pennsylvania, United States
| | - Michael H Santare
- Department of Mechanical Engineering, University of Delaware, United States
| | - Dawn M Elliott
- Department of Biomedical Engineering, University of Delaware, United States.
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Svensson RB, Herchenhan A, Starborg T, Larsen M, Kadler KE, Qvortrup K, Magnusson SP. Evidence of structurally continuous collagen fibrils in tendons. Acta Biomater 2017; 50:293-301. [PMID: 28063986 DOI: 10.1016/j.actbio.2017.01.006] [Citation(s) in RCA: 61] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2016] [Revised: 12/05/2016] [Accepted: 01/03/2017] [Indexed: 11/18/2022]
Abstract
Tendons transmit muscle-generated force through an extracellular matrix of aligned collagen fibrils. The force applied by the muscle at one end of a microscopic fibril has to be transmitted through the macroscopic length of the tendon by mechanisms that are poorly understood. A key element in this structure-function relationship is the collagen fibril length. During embryogenesis short fibrils are produced but they grow rapidly with maturation. There is some controversy regarding fibril length in adult tendon, with mechanical data generally supporting discontinuity while structural investigations favor continuity. This study initially set out to trace the full length of individual fibrils in adult human tendons, using serial block face-scanning electron microscopy. But even with this advanced technique the required length could not be covered. Instead a statistical approach was used on a large volume of fibrils in shorter image stacks. Only a single end was observed after tracking 67.5mm of combined fibril lengths, in support of fibril continuity. To shed more light on this observation, the full length of a short tendon (mouse stapedius, 125μm) was investigated and continuity of individual fibrils was confirmed. In light of these results, possible mechanisms that could reconcile the opposing findings on fibril continuity are discussed. STATEMENT OF SIGNIFICANCE Connective tissues hold all parts of the body together and are mostly constructed from thin threads of the protein collagen (called fibrils). Connective tissues provide mechanical strength and one of the most demanding tissues in this regard are tendons, which transmit the forces generated by muscles. The length of the collagen fibrils is essential to the mechanical strength and to the type of damage the tissue may experience (slippage of short fibrils or breakage of longer ones). This in turn is important for understanding the repair processes after such damage occurs. Currently the issue of fibril length is contentious, but this study provides evidence that the fibrils are extremely long and likely continuous.
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Affiliation(s)
- Rene B Svensson
- Institute of Sports Medicine Copenhagen, Department of Orthopedic Surgery M, Bispebjerg Hospital and Center for Healthy Aging, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.
| | - Andreas Herchenhan
- Institute of Sports Medicine Copenhagen, Department of Orthopedic Surgery M, Bispebjerg Hospital and Center for Healthy Aging, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Tobias Starborg
- Wellcome Trust Centre for Cell-Matrix Research, Faculty of Biology, Medicine and Health, University of Manchester, Manchester M13 9PT, United Kingdom
| | - Michael Larsen
- Core Facility for Integrated Microscopy, Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Karl E Kadler
- Wellcome Trust Centre for Cell-Matrix Research, Faculty of Biology, Medicine and Health, University of Manchester, Manchester M13 9PT, United Kingdom
| | - Klaus Qvortrup
- Core Facility for Integrated Microscopy, Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - S Peter Magnusson
- Institute of Sports Medicine Copenhagen, Department of Orthopedic Surgery M, Bispebjerg Hospital and Center for Healthy Aging, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
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9
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Harris KM, Spacek J, Bell ME, Parker PH, Lindsey LF, Baden AD, Vogelstein JT, Burns R. A resource from 3D electron microscopy of hippocampal neuropil for user training and tool development. Sci Data 2015; 2:150046. [PMID: 26347348 PMCID: PMC4555877 DOI: 10.1038/sdata.2015.46] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2015] [Accepted: 08/12/2015] [Indexed: 12/29/2022] Open
Abstract
Resurgent interest in synaptic circuitry and plasticity has emphasized the importance of 3D reconstruction from serial section electron microscopy (3DEM). Three volumes of hippocampal CA1 neuropil from adult rat were imaged at X-Y resolution of ~2 nm on serial sections of ~50-60 nm thickness. These are the first densely reconstructed hippocampal volumes. All axons, dendrites, glia, and synapses were reconstructed in a cube (~10 μm(3)) surrounding a large dendritic spine, a cylinder (~43 μm(3)) surrounding an oblique dendritic segment (3.4 μm long), and a parallelepiped (~178 μm(3)) surrounding an apical dendritic segment (4.9 μm long). The data provide standards for identifying ultrastructural objects in 3DEM, realistic reconstructions for modeling biophysical properties of synaptic transmission, and a test bed for enhancing reconstruction tools. Representative synapses are quantified from varying section planes, and microtubules, polyribosomes, smooth endoplasmic reticulum, and endosomes are identified and reconstructed in a subset of dendrites. The original images, traces, and Reconstruct software and files are freely available and visualized at the Open Connectome Project (Data Citation 1).
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Affiliation(s)
- Kristen M Harris
- Department of Neuroscience, Center for Learning and Memory, Institute for Neuroscience, University of Texas at Austin, 1 University Station C7000 , Austin, Texas 78712, USA
| | - Josef Spacek
- Department of Pathology, Charles University at Prague, Faculty of Medicine , 500 35 Hradec Kralove, Czech Republic
| | - Maria Elizabeth Bell
- Department of Neuroscience, Center for Learning and Memory, Institute for Neuroscience, University of Texas at Austin, 1 University Station C7000 , Austin, Texas 78712, USA
| | - Patrick H Parker
- Department of Neuroscience, Center for Learning and Memory, Institute for Neuroscience, University of Texas at Austin, 1 University Station C7000 , Austin, Texas 78712, USA
| | - Laurence F Lindsey
- Department of Neuroscience, Center for Learning and Memory, Institute for Neuroscience, University of Texas at Austin, 1 University Station C7000 , Austin, Texas 78712, USA
| | - Alexander D Baden
- Department of Computer Science, Institute for Data Intensive Science and Engineering, Johns Hopkins University, 160 Malone Hall, 3400 N. Charles St. , Baltimore, Maryland 21218, USA
| | - Joshua T Vogelstein
- Department of Biomedical Engineering, Institute for Computational Medicine, Johns Hopkins University, Clark Hall Room 317C, 3400 N. Charles St. , Baltimore, Maryland 21218, USA
| | - Randal Burns
- Department of Computer Science, Institute for Data Intensive Science and Engineering, Johns Hopkins University, 160 Malone Hall, 3400 N. Charles St. , Baltimore, Maryland 21218, USA
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10
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Ahmadzadeh H, Freedman BR, Connizzo BK, Soslowsky LJ, Shenoy VB. Micromechanical poroelastic finite element and shear-lag models of tendon predict large strain dependent Poisson's ratios and fluid expulsion under tensile loading. Acta Biomater 2015; 22:83-91. [PMID: 25934322 PMCID: PMC4466068 DOI: 10.1016/j.actbio.2015.04.035] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2014] [Revised: 04/12/2015] [Accepted: 04/23/2015] [Indexed: 11/28/2022]
Abstract
As tendons are loaded, they reduce in volume and exude fluid to the surrounding medium. Experimental studies have shown that tendon stretching results in a Poisson's ratio greater than 0.5, with a maximum value at small strains followed by a nonlinear decay. Here we present a computational model that attributes this macroscopic observation to the microscopic mechanism of the load transfer between fibrils under stretch. We develop a finite element model based on the mechanical role of the interfibrillar-linking elements, such as thin fibrils that bridge the aligned fibrils or macromolecules such as glycosaminoglycans (GAGs) in the interfibrillar sliding and verify it with a theoretical shear-lag model. We showed the existence of a previously unappreciated structure-function mechanism whereby the Poisson's ratio in tendon is affected by the strain applied and interfibrillar-linker properties, and together these features predict tendon volume shrinkage under tensile loading. During loading, the interfibrillar-linkers pulled fibrils toward each other and squeezed the matrix, leading to the Poisson's ratio larger than 0.5 and fluid expulsion. In addition, the rotation of the interfibrillar-linkers with respect to the fibrils at large strains caused a reduction in the volume shrinkage and eventual nonlinear decay in Poisson's ratio at large strains. Our model also predicts a fluid flow that has a radial pattern toward the surrounding medium, with the larger fluid velocities in proportion to the interfibrillar sliding.
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Affiliation(s)
- Hossein Ahmadzadeh
- Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, PA, USA
| | - Benjamin R Freedman
- McKay Orthopaedic Research Laboratory, University of Pennsylvania, Philadelphia, PA, USA
| | - Brianne K Connizzo
- McKay Orthopaedic Research Laboratory, University of Pennsylvania, Philadelphia, PA, USA
| | - Louis J Soslowsky
- McKay Orthopaedic Research Laboratory, University of Pennsylvania, Philadelphia, PA, USA
| | - Vivek B Shenoy
- Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, PA, USA.
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11
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Szczesny SE, Elliott DM. Interfibrillar shear stress is the loading mechanism of collagen fibrils in tendon. Acta Biomater 2014; 10:2582-90. [PMID: 24530560 DOI: 10.1016/j.actbio.2014.01.032] [Citation(s) in RCA: 107] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2013] [Revised: 12/04/2013] [Accepted: 01/30/2014] [Indexed: 12/15/2022]
Abstract
Despite the critical role tendons play in transmitting loads throughout the musculoskeletal system, little is known about the microstructural mechanisms underlying their mechanical function. Of particular interest is whether collagen fibrils in tendon fascicles bear load independently or if load is transferred between fibrils through interfibrillar shear forces. We conducted multiscale experimental testing and developed a microstructural shear lag model to explicitly test whether interfibrillar shear load transfer is indeed the fibrillar loading mechanism in tendon. Experimental correlations between fascicle macroscale mechanics and microscale interfibrillar sliding suggest that fibrils are discontinuous and share load. Moreover, for the first time, we demonstrate that a shear lag model can replicate the fascicle macroscale mechanics as well as predict the microscale fibrillar deformations. Since interfibrillar shear stress is the fundamental loading mechanism assumed in the model, this result provides strong evidence that load is transferred between fibrils in tendon and possibly other aligned collagenous tissues. Conclusively establishing this fibrillar loading mechanism and identifying the involved structural components should help develop repair strategies for tissue degeneration and guide the design of tissue engineered replacements.
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Affiliation(s)
- Spencer E Szczesny
- Department of Bioengineering, University of Pennsylvania, 240 Skirkanich Hall, 210 South 33rd St, Philadelphia, PA 19104, USA
| | - Dawn M Elliott
- Department of Biomedical Engineering, University of Delaware, 125 East Delaware Avenue, Newark, DE 19716, USA.
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12
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Three-dimensional aspects of matrix assembly by cells in the developing cornea. Proc Natl Acad Sci U S A 2014; 111:687-92. [PMID: 24385584 DOI: 10.1073/pnas.1313561110] [Citation(s) in RCA: 57] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Cell-directed deposition of aligned collagen fibrils during corneal embryogenesis is poorly understood, despite the fact that it is the basis for the formation of a corneal stroma that must be transparent to visible light and biomechanically stable. Previous studies of the structural development of the specialized matrix in the cornea have been restricted to examinations of tissue sections by conventional light or electron microscopy. Here, we use volume scanning electron microscopy, with sequential removal of ultrathin surface tissue sections achieved either by ablation with a focused ion beam or by serial block face diamond knife microtomy, to examine the microanatomy of the cornea in three dimensions and in large tissue volumes. The results show that corneal keratocytes occupy a significantly greater tissue volume than was previously thought, and there is a clear orthogonality in cell and matrix organization, quantifiable by Fourier analysis. Three-dimensional reconstructions reveal actin-associated tubular cell protrusions, reminiscent of filopodia, but extending more than 30 µm into the extracellular space. The highly extended network of these membrane-bound structures mirrors the alignment of collagen bundles and emergent lamellae and, we propose, plays a fundamental role in dictating the orientation of collagen in the developing cornea.
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13
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Starborg T, Kalson NS, Lu Y, Mironov A, Cootes TF, Holmes DF, Kadler KE. Using transmission electron microscopy and 3View to determine collagen fibril size and three-dimensional organization. Nat Protoc 2013; 8:1433-48. [PMID: 23807286 DOI: 10.1038/nprot.2013.086] [Citation(s) in RCA: 175] [Impact Index Per Article: 15.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Collagen fibrils are the major tensile element in vertebrate tissues, in which they occur as ordered bundles in the extracellular matrix. Abnormal fibril assembly and organization results in scarring, fibrosis, poor wound healing and connective tissue diseases. Transmission electron microscopy (TEM) is used to assess the formation of the fibrils, predominantly by measuring fibril diameter. Here we describe a protocol for measuring fibril diameter as well as fibril volume fraction, mean fibril length, fibril cross-sectional shape and fibril 3D organization, all of which are major determinants of tissue function. Serial-section TEM (ssTEM) has been used to visualize fibril 3D organization in vivo. However, serial block face-scanning electron microscopy (SBF-SEM) has emerged as a time-efficient alternative to ssTEM. The protocol described below is suitable for preparing tissues for TEM and SBF-SEM (by 3View). We describe how to use 3View for studying collagen fibril organization in vivo and show how to find and track individual fibrils. The overall time scale is ~8 d from isolating the tissue to having a 3D image stack.
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Affiliation(s)
- Tobias Starborg
- Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, University of Manchester, Manchester, UK
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Thompson MS. Tendon mechanobiology: experimental models require mathematical underpinning. Bull Math Biol 2013; 75:1238-54. [PMID: 23681792 DOI: 10.1007/s11538-013-9850-5] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2012] [Accepted: 04/25/2013] [Indexed: 10/26/2022]
Abstract
Mathematical and computational modeling is in demand to help address current challenges in mechanobiology of musculoskeletal tissues. In particular for tendon, the high clinical importance of the tissue, the huge mechanical demands placed on it and its ability to adapt to these demands, require coupled, multiscale models incorporating complex geometrical and microstructural information as well as time-based descriptions of cellular activity and response.This review introduces the information sources required to develop such multiscale models. It covers tissue structure and biomechanics, cell biomechanics, the current understanding of tendon's ability in health and disease to update its properties and structure and the few already existing multiscale mechanobiological models of the tissue. Finally, a sketch is provided of what such models could achieve ideally, pointing out where experimental data and knowledge are still missing.
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Affiliation(s)
- Mark S Thompson
- Institute of Biomedical Engineering, Botnar Research Centre, University of Oxford, Windmill Road, Oxford, OX3 7LD, UK.
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15
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Kuwajima M, Mendenhall JM, Lindsey LF, Harris KM. Automated transmission-mode scanning electron microscopy (tSEM) for large volume analysis at nanoscale resolution. PLoS One 2013; 8:e59573. [PMID: 23555711 PMCID: PMC3608656 DOI: 10.1371/journal.pone.0059573] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2012] [Accepted: 02/15/2013] [Indexed: 11/19/2022] Open
Abstract
Transmission-mode scanning electron microscopy (tSEM) on a field emission SEM platform was developed for efficient and cost-effective imaging of circuit-scale volumes from brain at nanoscale resolution. Image area was maximized while optimizing the resolution and dynamic range necessary for discriminating key subcellular structures, such as small axonal, dendritic and glial processes, synapses, smooth endoplasmic reticulum, vesicles, microtubules, polyribosomes, and endosomes which are critical for neuronal function. Individual image fields from the tSEM system were up to 4,295 µm2 (65.54 µm per side) at 2 nm pixel size, contrasting with image fields from a modern transmission electron microscope (TEM) system, which were only 66.59 µm2 (8.160 µm per side) at the same pixel size. The tSEM produced outstanding images and had reduced distortion and drift relative to TEM. Automated stage and scan control in tSEM easily provided unattended serial section imaging and montaging. Lens and scan properties on both TEM and SEM platforms revealed no significant nonlinear distortions within a central field of ∼100 µm2 and produced near-perfect image registration across serial sections using the computational elastic alignment tool in Fiji/TrakEM2 software, and reliable geometric measurements from RECONSTRUCT™ or Fiji/TrakEM2 software. Axial resolution limits the analysis of small structures contained within a section (∼45 nm). Since this new tSEM is non-destructive, objects within a section can be explored at finer axial resolution in TEM tomography with current methods. Future development of tSEM tomography promises thinner axial resolution producing nearly isotropic voxels and should provide within-section analyses of structures without changing platforms. Brain was the test system given our interest in synaptic connectivity and plasticity; however, the new tSEM system is readily applicable to other biological systems.
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Affiliation(s)
- Masaaki Kuwajima
- Center for Learning and Memory, The University of Texas at Austin, Austin, Texas, United States of America
| | - John M. Mendenhall
- Center for Learning and Memory, The University of Texas at Austin, Austin, Texas, United States of America
| | - Laurence F. Lindsey
- Center for Learning and Memory, The University of Texas at Austin, Austin, Texas, United States of America
| | - Kristen M. Harris
- Center for Learning and Memory, The University of Texas at Austin, Austin, Texas, United States of America
- Section of Neurobiology, The University of Texas at Austin, Austin, Texas, United States of America
- * E-mail:
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16
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Reese SP, Ellis BJ, Weiss JA. Micromechanical model of a surrogate for collagenous soft tissues: development, validation and analysis of mesoscale size effects. Biomech Model Mechanobiol 2013; 12:1195-204. [PMID: 23400805 DOI: 10.1007/s10237-013-0475-2] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2012] [Accepted: 01/25/2013] [Indexed: 01/10/2023]
Abstract
Aligned, collagenous tissues such as tendons and ligaments are composed primarily of water and type I collagen, organized hierarchically into nanoscale fibrils, microscale fibers and mesoscale fascicles. Force transfer across scales is complex and poorly understood. Since innervation, the vasculature, damage mechanisms and mechanotransduction occur at the microscale and mesoscale, understanding multiscale interactions is of high importance. This study used a physical model in combination with a computational model to isolate and examine the mechanisms of force transfer between scales. A collagen-based surrogate served as the physical model. The surrogate consisted of extruded collagen fibers embedded within a collagen gel matrix. A micromechanical finite element model of the surrogate was validated using tensile test data that were recorded using a custom tensile testing device mounted on a confocal microscope. Results demonstrated that the experimentally measured macroscale strain was not representative of the microscale strain, which was highly inhomogeneous. The micromechanical model, in combination with a macroscopic continuum model, revealed that the microscale inhomogeneity resulted from size effects in the presence of a constrained boundary. A sensitivity study indicated that significant scale effects would be present over a range of physiologically relevant inter-fiber spacing values and matrix material properties. The results indicate that the traditional continuum assumption is not valid for describing the macroscale behavior of the surrogate and that boundary-induced size effects are present.
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Affiliation(s)
- Shawn P Reese
- Department of Bioengineering, and Scientific Computing and Imaging Institute, University of Utah, Salt Lake City, UT, USA
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17
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Branching toughens fibrous networks. J Mech Behav Biomed Mater 2012; 12:74-82. [DOI: 10.1016/j.jmbbm.2012.03.011] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2011] [Revised: 03/05/2012] [Accepted: 03/14/2012] [Indexed: 11/23/2022]
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18
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Bella A, Ray S, Shaw M, Ryadnov MG. Arbitrary Self-Assembly of Peptide Extracellular Microscopic Matrices. Angew Chem Int Ed Engl 2011; 51:428-31. [DOI: 10.1002/anie.201104647] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2011] [Revised: 10/12/2011] [Indexed: 01/07/2023]
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19
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Bella A, Ray S, Shaw M, Ryadnov MG. Arbitrary Self-Assembly of Peptide Extracellular Microscopic Matrices. Angew Chem Int Ed Engl 2011. [DOI: 10.1002/ange.201104647] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
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20
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Wenstrup RJ, Smith SM, Florer JB, Zhang G, Beason DP, Seegmiller RE, Soslowsky LJ, Birk DE. Regulation of collagen fibril nucleation and initial fibril assembly involves coordinate interactions with collagens V and XI in developing tendon. J Biol Chem 2011; 286:20455-65. [PMID: 21467034 DOI: 10.1074/jbc.m111.223693] [Citation(s) in RCA: 95] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Collagens V and XI comprise a single regulatory type of fibril-forming collagen with multiple isoforms. Both co-assemble with collagen I or II to form heterotypic fibrils and have been implicated in regulation of fibril assembly. The objective of this study was to determine the roles of collagens V and XI in the regulation of tendon fibrillogenesis. Flexor digitorum longus tendons from a haplo-insufficient collagen V mouse model of classic Ehlers Danlos syndrome (EDS) had decreased biomechanical stiffness compared with controls consistent with joint laxity in EDS patients. However, fibril structure was relatively normal, an unexpected finding given the altered fibrils observed in dermis and cornea from this model. This suggested roles for other related molecules, i.e. collagen XI, and compound Col5a1(+/-),Col11a1(+/-) tendons had altered fibril structures, supporting a role for collagen XI. To further evaluate this, transcript expression was analyzed in wild type tendons. During development (E18-P10) both collagen V and XI were comparably expressed; however, collagen V predominated in mature (P30) tendons. The collagens had a similar expression pattern. Tendons with altered collagen V and/or XI expression (Col5a1(+/-); Col11a1(+/-); Col5a1(+/-),Col11a1(+/-); Col11a1(-/-); Col5a1(+/-),Col11a1(-/-)) were analyzed at E18. All genotypes demonstrated a reduced fibril number and altered structure. This phenotype was more severe with a reduction in collagen XI. However, the absence of collagen XI with a reduction in collagen V was associated with the most severe fibril phenotype. The data demonstrate coordinate roles for collagens V and XI in the regulation of fibril nucleation and assembly during tendon development.
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Kalson NS, Holmes DF, Kapacee Z, Otermin I, Lu Y, Ennos RA, Canty-Laird EG, Kadler KE. An experimental model for studying the biomechanics of embryonic tendon: Evidence that the development of mechanical properties depends on the actinomyosin machinery. Matrix Biol 2010; 29:678-89. [PMID: 20736063 PMCID: PMC3611596 DOI: 10.1016/j.matbio.2010.08.009] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2010] [Revised: 07/27/2010] [Accepted: 08/17/2010] [Indexed: 02/03/2023]
Abstract
Tendons attach muscles to bone and thereby transmit tensile forces during joint movement. However, a detailed understanding of the mechanisms that establish the mechanical properties of tendon has remained elusive because of the practical difficulties of studying tissue mechanics in vivo. Here we have performed a study of tendon-like constructs made by culturing embryonic tendon cells in fixed-length fibrin gels. The constructs display mechanical properties (toe-linear-fail stress-strain curve, stiffness, ultimate tensile strength, and failure strain) as well as collagen fibril volume fraction and extracellular matrix (ECM)/cell ratio that are statistically similar to those of embryonic chick metatarsal tendons. The development of mechanical properties during time in culture was abolished when the constructs were treated separately with Triton X-100 (to solubilise membranes), cytochalasin (to disassemble the actin cytoskeleton) and blebbistatin (a small molecule inhibitor of non-muscle myosin II). Importantly, these treatments had no effect on the mechanical properties of the constructs that existed prior to treatment. Live-cell imaging and (14)C-proline metabolic labeling showed that blebbistatin inhibited the contraction of the constructs without affecting cell viability, procollagen synthesis, or conversion of procollagen to collagen. In conclusion, the mechanical properties per se of the tendon constructs are attributable to the ECM generated by the cells but the improvement of mechanical properties during time in culture was dependent on non-muscle myosin II-derived forces.
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Key Words
- cvf, cell volume fraction, the fraction of the construct occupied by cells
- ecm, extracellular matrix
- ecmt, embryonic chick metatarsal tendon
- em, electron microscopy
- facs, fluorescence activated cell sorting
- fvf, fibril volume fraction, the fraction of the construct occupied by collagen fibrils
- nmmii, non-muscle myosin ii
- pbs, phosphate buffered saline
- bio-artificial tendon
- collagen
- elasticity
- electron microscopy
- extracellular matrix
- myosin
- fibril
- fibrin
- tension
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Affiliation(s)
- Nicholas S. Kalson
- Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, University of Manchester, Michael Smith Building, Oxford Road, Manchester M13 9PT, UK
| | - David F. Holmes
- Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, University of Manchester, Michael Smith Building, Oxford Road, Manchester M13 9PT, UK
| | - Zoher Kapacee
- Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, University of Manchester, Michael Smith Building, Oxford Road, Manchester M13 9PT, UK
| | - Iker Otermin
- Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, University of Manchester, Michael Smith Building, Oxford Road, Manchester M13 9PT, UK
| | - Yinhui Lu
- Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, University of Manchester, Michael Smith Building, Oxford Road, Manchester M13 9PT, UK
| | - Roland A. Ennos
- Faculty of Life Sciences, University of Manchester, Stopford Building, Oxford Road, Manchester M13 9PT, UK
| | - Elizabeth G. Canty-Laird
- Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, University of Manchester, Michael Smith Building, Oxford Road, Manchester M13 9PT, UK
| | - Karl E. Kadler
- Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, University of Manchester, Michael Smith Building, Oxford Road, Manchester M13 9PT, UK
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Bailey JL, Critser PJ, Whittington C, Kuske JL, Yoder MC, Voytik-Harbin SL. Collagen oligomers modulate physical and biological properties of three-dimensional self-assembled matrices. Biopolymers 2010; 95:77-93. [PMID: 20740490 DOI: 10.1002/bip.21537] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2010] [Revised: 08/10/2010] [Accepted: 08/11/2010] [Indexed: 01/09/2023]
Abstract
Elucidation of mechanisms underlying collagen fibril assembly and matrix-induced guidance of cell fate will contribute to the design and expanded use of this biopolymer for research and clinical applications. Here, we define how Type I collagen oligomers affect in-vitro polymerization kinetics as well as fibril microstructure and mechanical properties of formed matrices. Monomers and oligomers were fractionated from acid-solubilized pig skin collagen and used to generate formulations varying in monomer/oligomer content or average polymer molecular weight (AMW). Polymerization half-times decreased with increasing collagen AMW and closely paralleled lag times, indicating that oligomers effectively served as nucleation sites. Furthermore, increasing AMW yielded matrices with increased interfibril branching and had no correlative effect on fibril density or diameter. These microstructure changes increased the stiffness of matrices as evidenced by increases in both shear storage and compressive moduli. Finally, the biological relevance of modulating collagen AMW was evidenced by the ability of cultured endothelial colony forming cells to sense associated changes in matrix physical properties and alter vacuole and capillary-like network formation. This work documents the importance of oligomers as another physiologically-relevant design parameter for development and standardization of polymerizable collagen formulations to be used for cell culture, regenerative medicine, and engineered tissue applications.
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Affiliation(s)
- J L Bailey
- Weldon School of Biomedical Engineering, College of Engineering, Purdue University, West Lafayette, IN 47907, USA
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Kim YK, Gu LS, Bryan TE, Kim JR, Chen L, Liu Y, Yoon JC, Breschi L, Pashley DH, Tay FR. Mineralisation of reconstituted collagen using polyvinylphosphonic acid/polyacrylic acid templating matrix protein analogues in the presence of calcium, phosphate and hydroxyl ions. Biomaterials 2010; 31:6618-27. [PMID: 20621767 DOI: 10.1016/j.biomaterials.2010.04.060] [Citation(s) in RCA: 97] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2010] [Accepted: 04/29/2010] [Indexed: 10/19/2022]
Abstract
The complex morphologies of mineralised collagen fibrils are regulated through interactions between the collagen matrix and non-collagenous extracellular proteins. In the present study, polyvinylphosphonic acid, a biomimetic analogue of matrix phosphoproteins, was synthesised and confirmed with FTIR and NMR. Biomimetic mineralisation of reconstituted collagen fibrils devoid of natural non-collagenous proteins was demonstrated with TEM using a Portland cement-containing resin composite and a phosphate-containing fluid in the presence of polyacrylic acid as sequestration, and polyvinylphosphonic acid as templating matrix protein analogues. In the presence of these dual biomimetic analogues in the mineralisation medium, intrafibrillar and extrafibrillar mineralisation via bottom-up nanoparticle assembly based on the non-classical crystallisation pathway could be identified. Conversely, only large mineral spheres with no preferred association with collagen fibrils were observed in the absence of biomimetic analogues in the medium. Mineral phases were evident within the collagen fibrils as early as 4 h after the initially-formed amorphous calcium phosphate nanoprecursors were transformed into apatite nanocrystals. Selected area electron diffraction patterns of highly mineralised collagen fibrils were nearly identical to those of natural bone, with apatite crystallites preferentially aligned along the collagen fibril axes.
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Affiliation(s)
- Young Kyung Kim
- Department of Conservative Dentistry, School of Dentistry, Kyungpook National University, Daegu 700-412, Republic of Korea
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