Tensile rupture of medial arterial tissue studied by X-ray micro-tomography on stained samples

📝 Abstract

Detailed characterization of damage and rupture mechanics of arteries is one the current challenges in vascular biomechanics, which requires developing suitable experimental approaches. This paper introduces an approach using in situ tensile tests in an X-ray micro-tomography setup to observe mechanisms of damage initiation and progression in medial layers of porcine aortic samples. The technique requires the use of sodium polytungstate as a contrast agent, of which the conditions for use are detailed in this paper. Immersion of the samples during 24 hours in a 15 g.L-1 concentrated solution provided the best compromise for viewing musculo-elastic units in this tissue. The process of damage initiation, delamination and rupture of medial tissue under tensile loading was observed and can be described as an elementary process repeating several times until complete failure. This elementary process initiates with a sudden mode I fracture of a group of musculo-elastic units, followed by an elastic recoil of these units, causing mode II separation of these, hence a delamination plane. The presented experimental approach constitutes a basis for observation of other constituents, or for investigations on other tissues and damage mechanisms.

💡 Analysis

Detailed characterization of damage and rupture mechanics of arteries is one the current challenges in vascular biomechanics, which requires developing suitable experimental approaches. This paper introduces an approach using in situ tensile tests in an X-ray micro-tomography setup to observe mechanisms of damage initiation and progression in medial layers of porcine aortic samples. The technique requires the use of sodium polytungstate as a contrast agent, of which the conditions for use are detailed in this paper. Immersion of the samples during 24 hours in a 15 g.L-1 concentrated solution provided the best compromise for viewing musculo-elastic units in this tissue. The process of damage initiation, delamination and rupture of medial tissue under tensile loading was observed and can be described as an elementary process repeating several times until complete failure. This elementary process initiates with a sudden mode I fracture of a group of musculo-elastic units, followed by an elastic recoil of these units, causing mode II separation of these, hence a delamination plane. The presented experimental approach constitutes a basis for observation of other constituents, or for investigations on other tissues and damage mechanisms.

📄 Content

In situ tensile rupture test of medial arterial tissue in X-ray micro-tomography Clémentine Helfenstein-Didier1, Damien Taïnoff2, Julien Viville2, Jérôme Adrien2, Éric Maire2, Pierre Badel1

1 Univ Lyon, IMT Mines Saint-Etienne, Centre CIS, INSERM, SainBioSE, F - 42023 Saint-Etienne FRANCE 2 Université de Lyon, INSA-Lyon, MATEIS CNRS UMR5510, Villeurbanne, France

Article Type: technical note

Keywords: Aorta ; dissection ; rupture mechanism ; X-ray tomography ; in situ tensile test

*Corresponding Author: Pierre Badel, PhD., badel@emse.fr

Corresponding Author’s address:

Centre Ingénierie et Saanté

158 Cours Fauriel

42 023 SAINT-ETIENNE Cedex 2

Tel: +33 4 77 42 02 60

Manuscript Region of Origin: France

Word count (Introduction through Conclusion): 3211

Abstract
Detailed characterization of damage and rupture mechanics of arteries is one the current challenges in vascular biomechanics, which requires developing suitable experimental approaches. This paper introduces an approach using in situ tensile tests in an X-ray micro-tomography setup to observe mechanisms of damage initiation and progression in medial layers of porcine aortic samples. The technique requires the use of sodium polytungstate as a contrast agent, of which the conditions for use are detailed in this paper. Immersion of the samples during 24 hours in a 15 g.L-1 concentrated solution provided the best compromise for viewing musculo-elastic units in this tissue. The process of damage initiation, delamination and rupture of medial tissue under tensile loading was observed and can be described as an elementary process repeating several times until complete failure. This elementary process initiates with a sudden mode I fracture of a group of musculo-elastic units, followed by an elastic recoil of these units, causing mode II separation of these, hence a delamination plane. The presented experimental approach constitutes a basis for observation of other constituents, or for investigations on other tissues and damage mechanisms.

1. Introduction Detailed characterization of damage and rupture properties of arteries is one the current challenges in vascular biomechanics. Several approaches to characterize rupture and/or dissection properties of vascular tissues have been addressed (see for instance, the review (Tong et al., 2016) and references herein). A large proportion of this work was based on measured properties at the macroscopic scale that could serve the global understanding of the phenomenon and the development of constitutive models (Gasser et al., 2006). The use of histology helped in providing hints about the local effects of damage progression through the tissue. Towards a more complete description and understanding of arterial mechanics and damage, studies involving simultaneous mechanical loading and observations at the scales of the microstructure are necessary. Such studies are still scarce in the literature.
   Recently, several groups used multiphoton confocal microscopy (MPCM) to image the internal structure of arterial tissue (e.g. Rezakhaniha et al., 2012; Wang et al., 2013; Robertson et al., 2015). In these studies, the authors most often focused on collagen structures which are particularly (Robertson et al. 2015)suitable to be imaged using this type of microscope. These pioneering studies were the first to show the evolving geometry of collagen inside the arterial tissue under uniaxial and biaxial loading tests. Though this approach is very interesting and promising to provide deeper insight in the micro-scale mechanisms driving the mechanical response of such tissue, it turns out to be very difficult to setup, especially when combining it with mechanical tests. Its use in observing damage mechanisms still represents a challenge at the moment.
   Among other alternative non-destructive techniques, X-ray micro-tomography (XRCT) is probably one of the most accessible. 3D observations of biological tissues using this technique have already been proposed in the literature (Metscher et al., 2009a, 2009b, 2011; Johnson et al., 2006; Wirkner and Prendini, 2007). However, these studies were performed at larger scales. Other groups (Pauwels et al., 2013; Aslanidi et al., 2013a, 2013b; Jeffery et al., 2011; Mizutani et al., 2012; Walton et al., 2015) used high-Z element staining to investigate the structure of soft tissues at lower scales, for instance. However, none of them performed in situ tests, because, in Walton et al. (2015) for instance, specimens had to be paraffin-embedded and acquisition time was between 5 and 16 hours for one sample preventing from performing such tests. The scale that can be imaged using this technique is slightly larger than that of MPCM, but it offers an intermediate level that may be relevant for the study of arterial tissue, and for instance to investigate mechanisms like the propagation of dissection. In particul

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