A viscoelastic two-dimensional network model of the lung extracellular matrix
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ORIGINAL PAPER
A viscoelastic two‑dimensional network model of the lung extracellular matrix A. Iravani1 · A. Thambyah1 · K. S. Burrowes1,2 Received: 5 November 2019 / Accepted: 28 April 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The extracellular matrix (ECM) comprises a large proportion of the lung parenchymal tissue and is an important contributor to the mechanical properties of the lung. The lung tissue is a biologically active scaffold with a complex ECM matrix structure and composition that provides physical support to the surrounding cells. Nearly all respiratory pathologies result in changes in the structure and composition of the ECM; however, the impact of these alterations on the mechanical properties of the tissue is not well understood. In this study, a novel network model was developed to incorporate the combinatorial effect of lung tissue ECM constituents such as collagen, elastin and proteoglycans (PGs) and used to mimic the experimentally derived length–tension response of the tissue to uniaxial loading. By modelling the effect of collagen elasticity as an exponential function with strain, and in concert with the linear elastic response of elastin, the network model’s mechanical response matched experimental stress–strain curves from the literature. In addition, by incorporating spring–dashpot viscoelastic elements, to represent the PGs, the hysteresis response was also simulated. Finally, by selectively reducing volume fractions of the different ECM constituents, we were able to gain insight into their relative mechanical contribution to the larger scale tissue mechanical response. Keywords Extracellular matrix · Lung · Viscoelastic properties · Network model
1 Introduction The extracellular matrix (ECM) is a biologically active three-dimensional scaffold that provides structural and biochemical support to surrounding cells. All tissues are comprised of ECM; however, the composition and resultant mechanical properties vary depending on the tissue type and the required function thereof. ECM of the lung parenchyma is composed of three main components: collagen and elastin within a proteoglycan (PG) viscous matrix comprising the remainder. Collagen provides strength and structural Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10237-020-01336-1) contains supplementary material, which is available to authorized users. * K. S. Burrowes [email protected] 1
Department of Chemical and Materials Engineering, University of Auckland, Auckland, New Zealand
Auckland Bioengineering Institute, University of Auckland, 70 Symonds Street, Auckland, New Zealand
2
support, elastin gives the lung its characteristic elasticity, a requirement for normal breathing, and PGs provide cushioning and stability during tissue loading. In healthy lung parenchyma, collagen type I has been measured to comprise 8% and elastin 10% of total tissue area. These fractions have been found to vary within different parts of a health
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