Tendon‐bone insertion is a functionally graded tissue, transitioning from 200 MPa tensile modulus at the tendon end to 20 GPa tensile modulus at the bone, across just a few hundred micrometers. In this study, we examine the porcine digital flexor tendon insertion tissue to provide a quantitative description of its collagen orientation and mineral concentration by using Fast Fourier Transform (FFT) based image analysis and mass spectrometry, respectively. Histological results revealed uniformity in global collagen orientation at all depths, indicative of mechanical anisotropy, although at mid‐depth, the highest fiber density, least amount of dispersion, and least cellular circularity were evident. Collagen orientation distribution obtained through 2D FFT of histological imaging data from fluorescent microscopy agreed with past measurements based on polarized light microscopy. Results revealed global fiber orientation across the tendon‐bone insertion to be preserved along direction of physiologic tension. Gradation in the fiber distribution orientation index across the insertion was reflective of a decrease in anisotropy from the tendon to the bone. We provided elemental maps across the fibrocartilage for its organic and inorganic constituents through time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS). The apatite intensity distribution from the tendon to bone was shown to follow a linear trend, supporting past results based on Raman microprobe analysis. The merit of this study lies in the image‐based simplified approach to fiber distribution quantification and in the high spatial resolution of the compositional analysis. In conjunction with the mechanical properties of the insertion tissue, fiber, and mineral distribution results for the insertion from this may potentially be incorporated into the development of a structural constitutive approach toward computational modeling. Characterizing the properties of the native insertion tissue would provide the microstructural basis for developing biomimetic scaffolds to recreate the graded morphology of a fibrocartilaginous insertion. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 3050–3058, 2017.
A pilot study on biaxial mechanical, collagen microstructural, and morphological characterizations of a resected human intracranial aneurysm tissue
Intracranial aneurysms (ICAs) are focal dilatations that imply a weakening of the brain artery. Incidental rupture of an ICA is increasingly responsible for significant mortality and morbidity in the American’s aging population. Previous studies have quantified the pressure-volume characteristics, uniaxial mechanical properties, and morphological features of human aneurysms. In this pilot study,
- NSF-PAR ID:
- 10213400
- Publisher / Repository:
- Nature Publishing Group
- Date Published:
- Journal Name:
- Scientific Reports
- Volume:
- 11
- Issue:
- 1
- ISSN:
- 2045-2322
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract We propose a novel structure-based two-dimensional (2D) mathematical model of hypertension-induced arterial remodeling. The model is built in the framework of the constrained mixture theory and global growth approach, utilizing a recently proposed structure-based constitutive model of arterial tissue that accounts for the individual natural configurations of and stress interaction between elastin and collagen. The basic novel predictive result is that provided remodeling causes a change in the elastin/collagen mass fraction ratio, it leads to a structural reorganization of collagen that manifests as an altered fiber undulation and a change in direction of the helically oriented fibers in the tissue natural state. Results obtained from the illustrative simulations for a porcine renal artery show that when remodeling is complete the collagen reorganization might have significant effects on the initial arterial geometry and mechanical properties of the arterial tissue. The proposed model has potential to describe and advance mechanistic understanding of adaptive arterial remodeling, promote the continual refinement of mathematical models of arterial remodeling, and provide motivation for new avenues of experimental investigation.more » « less
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null (Ed.)Introduction: Vascular diseases like abdominal aortic aneurysms (AAA) are characterized by a drastic remodeling of the vessel wall, accompanied with changes in the elastin and collagen content. At the macromolecular level, the elastin fibers in AAA have been reported to undergo significant structural alterations. While the undulations (waviness) of the collagen fibers is also reduced in AAA, very little is understood about changes in the collagen fibril at the sub-fiber level in AAA as well as in other vascular pathologies. Materials and Methods: In this study we investigated structural changes in collagen fibrils in human AAA tissue extracted at the time of vascular surgery and in aorta extracted from angiotensin II (AngII) infused ApoE−/− mouse model of AAA. Collagen fibril structure was examined using transmission electron microscopy and atomic force microscopy. Images were analyzed to ascertain length and depth of D-periodicity, fibril diameter and fibril curvature. Tissues were also stained using collagen hybridizing peptide (CHP) and analyzed using fluorescent microscopy and second harmonic generation (SHG) microscopy to locate regions of healthy and degraded collagen. Results: Abnormal collagen fibrils with compromised D-periodic banding were observed in the excised human tissue and in remodeled regions of AAA in AngII infused mice (Figure 1). These abnormal fibrils were characterized by statistically significant reduction in depths of D-periods and an increased curvature of collagen fibrils. These features were more pronounced in human AAA as compared to murine samples. Additionally, regions of abnormal collagen were located within the remodeled areas of AAA tissue and were distinct from healthy collagen regions as ascertained using CHP staining and SHG (Figure 1). Thoracic aorta from Ang II-infused mice, abdominal aorta from saline-infused mice, and abdominal aorta from non-AAA human controls did not contain abnormal collagen fibrils. Conclusions: The structural alterations in abnormal collagen fibrils appear similar to those reported for collagen fibrils subjected to mechanical overload or chronic inflammation in other tissues. Detection of abnormal collagen could be utilized to better understand the functional properties of the underlying extracellular matrix in vascular as well as other pathologies.more » « less
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