Transverse mechanical properties of collagen fibers from nanoindentation (original) (raw)
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Mechanical Properties of Collagen Fibrils
Biophysical Journal, 2007
The formation of collagen fibers from staggered subfibrils still lacks a universally accepted model. Determining the mechanical properties of single collagen fibrils (diameter 50-200 nm) provides new insights into collagen structure. In this work, the reduced modulus of collagen was measured by nanoindentation using atomic force microscopy. For individual type 1 collagen fibrils from rat tail, the modulus was found to be in the range from 5 GPa to 11.5 GPa (in air and at room temperature). The hypothesis that collagen anisotropy is due to the subfibrils being aligned along the fibril axis is supported by nonuniform surface imprints performed by high load nanoindentation.
Mechanical properties of collagen fibrils and elastic fibers explored by AFM
Journal of Physics Conference Series, 2008
Micromechanical properties of single elastic fibers and fibrillin-microfibrils, isolated from equine ligamentum nuchae using chemical and enzymatic methods were determined with atomic force microscopy (AFM). Young's moduli of single elastic fibers immersed in water, devoid of or containing fibrillin-microfibrils, were determined using bending tests. Bending freely suspended elastic fibers on a micro-channeled substrate by a tip-less AFM cantilever generated a force versus displacement curve from which the Young's modulus was calculated. For single elastic fibers, Young's moduli in the range of 0.3-1.5 MPa were determined, values not significantly affected by the absence or presence of fibrillinmicrofibrils. To further understand the role of fibrillin-microfibrils in vertebrate elastic fibers, layers of fibrillin-microfibrils were subjected to nano-indentation tests. From the * This chapter is to be submitted for publication. † Authors contribute equally to this work.
Mechanical and Structural Properties of Collagen Nanofribrous Layers Under Simulated Body Conditions
Acta Polytechnica CTU Proceedings, 2019
The theme of this paper is the analysis of mechanical and structural properties of nanofibrous COL under simulated body conditions and in the presence of osteoblasts and dermal fibroblasts. COL were prepared by electrostatic spinning of 8wt% collagen type I dispersion with 8wt% (to COL) of PEG in phosphate buffer/ethanol solution (1/1vol). The stability of COL was enhanced by means of cross-linking with EDC and NHS at a molar ratio of 4:1. COL were exposed in culture medium for 21 days and human SAOS-2 human dermal fibroblasts and osteoblasts were cultured therein for 21 days as well. The cell culture on COL was assessed by fluorescence microscopy and metabolic activity. Then the metabolic activity of both cell types grown on COL and PS were measured after 1, 7, 14 and 21 days using the Alamar Blue assay method. Mechanical properties were determined using an tensile test. The influence of the cell activity on secondary structure of COL was verified by IR spectroscopy. Furthermore, the influ...
Nanomechanics of Type I Collagen
Biophysical journal, 2016
Type I collagen is the predominant collagen in mature tendons and ligaments, where it gives them their load-bearing mechanical properties. Fibrils of type I collagen are formed by the packing of polypeptide triple helices. Higher-order structures like fibril bundles and fibers are assembled from fibrils in the presence of other collagenous molecules and noncollagenous molecules. Curiously, however, experiments show that fibrils/fibril bundles are less resistant to axial stress compared to their constituent triple helices-the Young's moduli of fibrils/fibril bundles are an order-of-magnitude smaller than the Young's moduli of triple helices. Given the sensitivity of the Young's moduli of triple helices to solvation environment, a plausible explanation is that the packing of triple helices into fibrils perhaps reduces the Young's modulus of an individual triple helix, which results in fibrils having smaller Young's moduli. We find, however, from molecular dynamics ...
Mechanical Properties of Native and Cross-linked Type I Collagen Fibrils
Biophysical Journal, 2008
Micromechanical bending experiments using atomic force microscopy were performed to study the mechanical properties of native and carbodiimide-cross-linked single collagen fibrils. Fibrils obtained from a suspension of insoluble collagen type I isolated from bovine Achilles tendon were deposited on a glass substrate containing microchannels. Forcedisplacement curves recorded at multiple positions along the collagen fibril were used to assess the bending modulus. By fitting the slope of the force-displacement curves recorded at ambient conditions to a model describing the bending of a rod, bending moduli ranging from 1.0 GPa to 3.9 GPa were determined. From a model for anisotropic materials, the shear modulus of the fibril is calculated to be 33 6 2 MPa at ambient conditions. When fibrils are immersed in phosphate-buffered saline, their bending and shear modulus decrease to 0.07-0.17 GPa and 2.9 6 0.3 MPa, respectively. The two orders of magnitude lower shear modulus compared with the Young's modulus confirms the mechanical anisotropy of the collagen single fibrils. Crosslinking the collagen fibrils with a water-soluble carbodiimide did not significantly affect the bending modulus. The shear modulus of these fibrils, however, changed to 74 6 7 MPa at ambient conditions and to 3.4 6 0.2 MPa in phosphate-buffered saline.
Biophysical Journal, 1997
Collagen is the primary structural element in extracellular matrices. In the form of fibers it acts to transmit forces, dissipate energy, and prevent premature mechanical failure in normal tissues. Deformation of collagen fibers involves molecular stretching and slippage, fibrillar slippage, and, ultimately, defibrillation. Our laboratory has developed a process for self-assembly of macroscopic collagen fibers that have structures and mechanical properties similar to rat tail tendon fibers. The purpose of this study is to determine the effects of subfibrillar orientation and decorin incorporation on the mechanical properties of collagen fibers. Self-assembled collagen fibers were stretched 0-50% before cross-linking and then characterized by microscopy and mechanical testing. Results of these studies indicate that fibrillar orientation, packing, and ultimate tensile strength can be increased by stretching. In addition, it is shown that decorin incorporation increases ultimate tensile strength of uncross-linked fibers. Based on the observed results it is hypothesized that decorin facilitates fibrillar slippage during deformation and thereby improves the tensile properties of collagen fibers.
Materials Science and Mechanics of Collagenous Tissues
Research & Reviews: Journal of Material Sciences, 2017
Collagen is the most abundant protein found in the extracellular matrix (ECM) of vertebrates. It forms the fibrous backbone or parenchyma of many tissues, the support for cells at tissue interfaces, and is the primary structural component of the musculoskeletal system. The collagen family is composed of several collagen subfamilies including fibril forming collagens, beaded filaments, anchoring fibrils and network forming collagens [1]. The structural stability of tissues is the result of the formation of collagen fibrils, fibril bundles, fibers and fascicles in tendon, and in other tissues collagen fibrils and fibers are the structural components. Most collagen fibrils are composites since they are made up of more than one collagen types such as tendon (types I, II and V), cartilage (types II, IX and XI), skin (types I and III) and cornea (types I, III and V). In addition, other non-collagenous macromolecules are attached to collagen fibrils that are involved in fibril formation (proteoglycans), cell-collagen interactions (fibronectin) and mechanotransduction (integrins) [1]. The purpose of this paper is to relate the structural hierarchy of collagen fibrils and fibers to the mechanical behavior of collagenous tissues to help better understand the function of collagen in health and disease. Mechanical and Metabolic Roles of Collagen in Tissues Collagen fibers in vertebrate extracellular matrix (ECM) serve important mechanical roles including preventing premature mechanical failure and modulation of force transfer between neighboring tissues [2,3]. They store elastic energy during muscular deformation, transmit stored energy resulting in joint movement, transfer excess energy from the joint back to the attached muscles for dissipation and promote regulation of cell and tissue synthesis through a process known as mechanochemical transduction [4]. They act as mechanotransducers by transferring stress borne by the musculoskeleton and other tissues to the attached cells in order and regulate tissue metabolism, either up-or down, as a result of changes in mechanical loading [3]. Collagen fibers transduce mechanical loading into changes in chemical synthesis of proteins which leads to energy storage in the form of high ABSTRACT Collagen is the major structural protein found in mammalian extracellular matrix (ECM). ECMs act as biological mechanotransducers that prevent premature mechanical failure of tissues, store and transmit energy created by muscular deformation, and amplify protein synthesis and cell division as the applied stress and loads are increased (mechanochemical transduction). Fibrous collagens play important roles in health and disease processes much of which depends on the mechanical properties of these tissues. The purpose of this paper is to summarize our knowledge of relationship between the structure and mechanical properties of fibrous collagens in vertebrates.
Nanomechanical Mapping of Hydrated Rat Tail Tendon Collagen I Fibrils
Biophysical Journal, 2014
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 mm 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.
Fibrillar Structure and Mechanical Properties of Collagen
Collagen type I is among the most important stress-carrying protein structures in mammals. Despite their importance for the outstanding mechanical properties of this tissue, there is still a lack of understanding of the processes that lead to the specific shape of the stress–strain curve of collagen. Recent in situ synchrotron X-ray scattering experiments suggest that several different processes could dominate depending on the amount of strain. While at small strains there is a straightening of kinks in the collagen structure, first at the fibrillar then at the molecular level, higher strains lead to molecular gliding within the fibrils and ultimately to a disruption of the fibril structure. Moreover, it was observed that the strain within collagen fibrils is always considerably smaller than in the whole tendon. This phenomenon is still very poorly understood but points toward the existence of additional gliding processes occurring at the interfibrillar level. 1997 Academic Press
Mechanical characterization of collagen fibers and scaffolds for tissue engineering
Biomaterials, 2003
Engineered tissues must utilize scaffolding biomaterials that support desired cellular functions and possess or can develop appropriate mechanical characteristics. This study assessed properties of collagen as a scaffolding biomaterial for ligament replacements. Mechanical properties of extruded bovine achilles tendon collagen fibers were significantly affected by fiber diameter, with smaller fibers displaying higher tangent moduli and peak stresses. Mechanical properties of 125 mm-diameter extruded fibers (tangent modulus of 359.6728.4 MPa; peak stress of 36.075.4 MPa) were similar to properties reported for human ligaments. Scaffolds of extruded fibers did not exhibit viscoelastic creep properties similar to natural ligaments. Collagen fibers from rat tail tendon (a well-studied comparison material) displayed characteristic strain-softening behavior, and scaffolds of rat tail fibers demonstrated a non-intuitive relationship between tangent modulus and specimen length. Composite scaffolds (extruded collagen fibers cast within a gel of Type I rat tail tendon collagen) were maintained with and without fibroblasts under standard culture conditions for 25 days; cell-incorporated scaffolds displayed significantly higher tangent moduli and peak stresses than those without cells. Because tissue-engineered products must possess appropriate mechanical as well as biological/chemical properties, data from this study should help enable the development of improved tissue analogues. r