Three dimensional microstructural network of elastin, collagen, and cells in Achilles tendons

Abstract

Similar to most biological tissues, the biomechanical, and functional characteristics of the Achilles tendon are closely related to its composition and microstructure. It is commonly reported that type I collagen is the predominant component of tendons and is mainly responsible for the tissue's function. Although elastin has been found in varying proportions in other connective tissues, previous studies report that tendons contain very small quantities of elastin. However, the morphology and the microstructural relationship among the elastic fibres, collagen, and cells in tendon tissue have not been well examined. We hypothesize the elastic fibres, as another fibrillar component in the extracellular matrix, have a unique role in mechanical function and microstructural arrangement in Achilles tendons. It has been shown that elastic fibres present a close connection with the tenocytes. The close relationship of the three components has been revealed as a distinct, integrated and complex microstructural network. Notably, a "spiral" structure within fibril bundles in Achilles tendons was observed in some samples in specialized regions. This study substantiates the hierarchical system of the spatial microstructure of tendon, including the mapping of collagen, elastin and tenocytes, with 3-dimensional confocal images. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1203-1214, 2017.

Evidence that interfibrillar load transfer in tendon is supported by small diameter fibrils and not extrafibrillar tissue components

“…Nevertheless, assuming elastin was not digested by trypsin, it appears unlikely that elastin fibers serve to transmit load between collagen fibrils. First, elastin fibers are distinct structures with a spatial distribution separate from collagen fibrils . Second, previous elastase digestions of rat tail tendon fascicles and porcine ligaments produced no changes in the macroscale tensile modulus, suggesting that elastin (or any additional tissue components removed by elastase) is not involved in load transfer between collagen fibrils.…”

Comparative multi‐scale hierarchical structure of the tail, plantaris, and Achilles tendons in the rat

“…; Pang et al. ). Immediately after sacrifice and dissection, the tendon was incubated in Dulbecco's modified Eagle medium (DMEM) culture medium supplemented with 25 m m HEPES, 1% penicillin, and 1% streptomycin (Thermo Fisher Scientific) for 30 min at 37 °C.…”

“…To test our hypothesis that cells outline fibers in tendon, we acquired SHG signals for the collagen alignment and fluorescence from cell for the cell placement. SHG microscopy is a nonlinear optical method that can visualize collagen without additional staining or processing (Fung et al 2010a,b;Chen et al 2012;Pang et al 2017). Immediately after sacrifice and dissection, the tendon was incubated in Dulbecco's modified Eagle medium (DMEM) culture medium supplemented with 25 mM HEPES, 1% penicillin, and 1% streptomycin (Thermo Fisher Scientific) for 30 min at 37°C.…”

Tendon exhibits complex poroelastic behavior at the nanoscale as revealed by high-frequency AFM-based rheology

“…Tendon fascicles were gently harvested with tweezers from the tails of 2–3 month old Sprague-Dawley rats sacrificed for an unrelated study. Rat tail tendon fascicles contain the essential collagenous components of tendon in the most simplified and aligned structure, while the Achilles and supraspinatus tendons are more complex in structure and are more clinically relevant for tendon disease and injury (Fallon et al, 2002; Herod et al, 2016; Pang et al, 2016; Rowe, 1985; Screen et al, 2015). In this study, we used the rat tail tendon fascicles to study the behavior of the most simplified tendon structure and composition (highly aligned collagen fibrils and organized distribution of extracellular matrix proteins), and the mouse supraspinatus and Achilles tendons to investigate the role of the tendon-to-bone junction, as well as the more complicated composition and structure (inhomogeneous fibril packing and fibril size/shape, increased inhomogeneity in type and distribution of proteoglycans, and decreased collagen organization), in the poroelastic response.…”