Coherent X-Ray Imaging of Collagen Fibril Distributions within Intact Tendons

Berenguer, Felisa; Bean, Richard; Bozec, Laurent; Vila‐Comamala, Joan; Zhang, Fucai; Kewish, Cameron M.; Bunk, Oliver; Rodenburg, J. M.; Robinson, Ian

doi:10.1016/j.bpj.2013.12.016

Cited by 14 publications

(8 citation statements)

References 39 publications

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“…Collagen fibrils are predominantly aligned in parallel along the direction of loading, in the form of the well-organized bundles[33,34]. Among all the fibrils, electron microscopy has identified smaller diameter fibrils that traverse and bifurcate with larger diameter fibrils [17,35,36].…”

Section: Introductionmentioning

confidence: 99%

Micromechanical poroelastic finite element and shear-lag models of tendon predict large strain dependent Poisson’s ratios and fluid expulsion under tensile loading

et al. 2015

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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 are bridging between 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 towards 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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Section: Introductionmentioning

confidence: 99%

Micromechanical poroelastic finite element and shear-lag models of tendon predict large strain dependent Poisson’s ratios and fluid expulsion under tensile loading

et al. 2015

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“…3 Our assumption of a global D-band follows previous theoretical treatment of D-banded fibrils, 19 and from the experimental observation of a robust, well-defined, global D-band for a wide variety of fibril radii. 5,[33][34][35] This assumption also considerably simplifies our approach.…”

Section: Modelmentioning

confidence: 99%

Non-equilibrium Growth and Twist of Cross-Linked Collagen Fibrils

Leighton,

Kreplak,

Rutenberg

2020

Preprint

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The lysyl oxidase (LOX) enzyme that catalyses cross-link formation during the assembly of collagen fibrils in vivo is too large to diffuse within assembled fibrils, and so is incompatible with a fully equilibrium mechanism for fibril formation. We propose that enzymatic cross-links are formed at the fibril surface during the growth of collagen fibrils; as a consequence no significant reorientation of previously cross-linked collagen molecules occurs inside collagen fibrils during fibril growth in vivo. By imposing local equilibrium only at the fibril surface, we develop a coarse-grained quantitative model of in vivo fibril structure that incorporates a double-twist orientation of collagen molecules and a periodic D-band density modulation along the fibril axis. Radial growth is controlled by the density of available collagen molecules around the fibril. In contrast with earlier equilibrium models of fibril structure, we find that all fibrils can exhibit a core-shell structure that is controlled only by the fibril radius. At small radii a core is developed with a linear double-twist structure as a function of radius. Within the core the double-twist structure is largely independent of the D-band. Within the shell at larger radii, the structure approaches a constant twist configuration that is strongly coupled with the D-band. We suggest a stable radius control mechanism that corneal fibrils can exploit near the edge of the linear core regime; while larger tendon fibrils can use a cruder version of growth control that does not select a preferred radius.

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“…Although there continues to be progress in superresolution techniques using ptychography in electron microscopy [19,20], the successful production of hardware based aberration correctors and their widespread use in high resolution TEM and STEM now provides a direct route for enhanced resolution and sensitivity for incoherent imaging modes such as ADF and EELS. There have also been been recent advances in both X-ray and light microscopy [21,22,23,24,25] using ptchography. However, ptychography still holds great potential for use in high resolution transmission electron microscopy.…”

Section: Introductionmentioning

confidence: 99%

Efficient phase contrast imaging in STEM using a pixelated detector. Part 1: Experimental demonstration at atomic resolution

et al. 2015

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We demonstrate a method to achieve high efficiency phase contrast imaging in aberration corrected scanning transmission electron microscopy (STEM) with a pixelated detector. The pixelated detector is used to record the Ronchigram as a function of probe position which is then analyzed with ptychography. Ptychography has previously been used to provide super-resolution beyond the diffraction limit of the optics, alongside numerically correcting for spherical aberration. Here we rely on a hardware aberration corrector to eliminate aberrations, but use the pixelated detector data set to utilize the largest possible volume of Fourier space to create high efficiency phase contrast images. The use of ptychography to diagnose the effects of chromatic aberration is also demonstrated. Finally, the four dimensional dataset is used to compare different bright field detector configurations from the same scan for a sample of bilayer graphene. Our method of high efficiency ptychography produces the clearest images, while annular bright field produces almost no contrast for an in-focus aberration-corrected probe.

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Coherent X-Ray Imaging of Collagen Fibril Distributions within Intact Tendons

Cited by 14 publications

References 39 publications

Micromechanical poroelastic finite element and shear-lag models of tendon predict large strain dependent Poisson’s ratios and fluid expulsion under tensile loading

Micromechanical poroelastic finite element and shear-lag models of tendon predict large strain dependent Poisson’s ratios and fluid expulsion under tensile loading

Non-equilibrium Growth and Twist of Cross-Linked Collagen Fibrils

Efficient phase contrast imaging in STEM using a pixelated detector. Part 1: Experimental demonstration at atomic resolution

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