FT-Raman spectroscopic study of thoracic aortic wall subjected to uniaxial stress (original) (raw)
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Mechanobiology of soft tissues: FT-Raman spectroscopic studies
Challenges of Modern Technology, 2011
FT-Raman spectroscopy was used to investigate microstructural changes in the secondary protein structure of soft tissues subjected to increasing levels of macroscopic strain. Main protein bands at 938 cm-1 assigned as ν(C–C), 1668 cm-1 — amide I and 1268 cm-1 — amide III are sensitive to applied strain and undergo wavenumber shifting. Other main vibrational modes at 1004 cm-1 assigned to the phenyl ring breathing mode and 2940 cm-1 (n(CH3,CH2)) remain unaltered. Spectroscopic results were compared with the mechanical relations obtained from the standard protocol of uniaxial tensile tests carried out in a testing machine. A clear correlation between Raman band shifting and the level of mechanical stress was established. Initially the load is transferred through elastin and then gradually also by collagen. It was proved that transferring loads by soft tissues involves changes in structural protein conformation. Th is process was described in detail for a tendon. It was also confi rme...
The role of elastin and collagen in the softening behavior of the human thoracic aortic media
Journal of Biomechanics, 2013
In a previous study we were able to accurately fit experimental data on arterial tissues at supraphysiological loads using a material model that accounts for softening/damage only in the portion of the model associated with the collagen fibers (Weisbecker et al., 2012). Naturally, this result leads to the hypothesis that the softening behavior is related only to the collagen fibers, and not to the matrix material. In this study we test this hypothesis by conducting uniaxial extension tests on elastase and collagenase treated tissues and on untreated control specimens from the media of human thoracic aortas. We relate structural changes in the tissue after enzyme treatment to changes in the corresponding mechanical behavior. Collagenase treated tissue does not exhibit any softening behavior under quasistatic cyclic loading, a result supporting our hypothesis. Conversely, elastase treated tissue exhibits continuous softening under the same loading conditions, indicating that the integrity of the tissue is destroyed upon removal of the elastin. Finally, we fit isotropic and anisotropic constitutive models to the mechanical response of the collagenase treated arterial tissue, while our anisotropic model better approximates the response of collagenase treated arterial tissues, we show that an isotropic matrix model is sufficient to accurately reproduce the mechanical response of untreated control specimens, consistent with current practice in the literature.
FT-Raman spectroscopic study of human skin subjected to uniaxial stress
Journal of the Mechanical Behavior of Biomedical Materials
Fourier Transform Raman Spectroscopy was used to investigate the molecular changes of structural proteins in human skin subjected to strain. In the Raman spectrum of unstrained skin, bands assigned mainly to collagen and elastin were observed at 1658cm(-1) (amide I), 1271 and 1255cm(-1) (amide III), and 935 and 817cm(-1) (CC stretching modes of the protein backbone). Moreover, bands characteristic for amino acids were observed at 1336cm(-1) (desmosine), 1004cm(-1) (phenylalanine), 919 and 856cm(-1) (proline), and 877cm(-1) (hydroxyproline). Positions and intensities of the listed Raman bands were analysed as a function of applied strain. A clear correlation between Raman wavenumbers and the level of mechanical stress was established. Wavenumbers of the analysed bands changed gradually with increasing strain. Distinct responses, depending on the sample cutting direction, i.e. longitudinal or perpendicular to the Langer's lines, were noticed. It was concluded that elastin and non...
Structural alteration of collagen fibres--spectroscopic and mechanical studies
Acta of bioengineering and biomechanics / Wrocław University of Technology, 2010
Fourier Transform Near Infrared Raman Spectroscopy has been used to monitor the molecular changes of collagen in a tendon subjected to strain. In the Raman spectrum of the unstrained tendon, some protein bands, mainly assigned to collagen, can be observed: amide I (1666 cm-1) and III (1266 and 1248 cm-1) vibrational modes and skeletal (C-C) stretching vibrations (816 and 940 cm-1). The position of these bands is changing with the increasing strain values. It is concluded that elastin and non-helical domains of collagen are initially involved in the load transfer and triple helices of collagen are gradually joining this process.
Influence of selective digestion of elastin and collagen on mechanical properties of human aortas
Acta of Bioengineering and Biomechanics, 2015
Purpose: There are two families of fibres taking part in the process of mechanical loads transfer, i.e. elastin and collagen fibres. Their number, spatial arrangement and specific properties determine the capacity of a blood vessels to resist mechanical loads resulting from the impact of blood on vessel walls. The purpose of the present paper is to define the load-bearing capacities of elastin and collagen scaffolds equivalent to natural fibre arrangements of human aorta and produced by selective digestion. Methods: Samples of thoracic human aortas were digested by using phosphate buffer of trypsin at pH 8.0 for 22 hours in order to degrade elastin and by autoclaving followed by incubation in 90% formic acid for 22 hours. The efficacy of digestion was assessed immunohistochemically. Mechanical properties of pre-stretched native and digested samples were determined by uniaxial tensile test. Results: Samples subjected to autoclaving have been successfully deprived of both types of collagen and elastin has been intact. Treatment with trypsin caused a removal of elastin and the presence of type I and IV collagen was demonstrated. Digestion of aortic samples either by formic acid or trypsin has resulted significantly decreasing mechanical properties in comparison with native samples. Conclusions: Collagen and elastin scaffold-like stuctures have been effectively produced by selective digestion of thoracic human aorta and their contribution to the load-bearing process was evaluated. Isolated collagen network are more durable and stiffer and less deformable than elastin network, hence are responsible for load-bearing process at higher strain since the range of working of elastin is at lower strain values.
Biomacromolecules, 2011
Collagen is a versatile structural molecule in nature and is used as a building block in many highly organized tissues, such as bone, skin, and cornea. The functionality and performance of these tissues are controlled by their hierarchical organization ranging from the molecular up to macroscopic length scales. In the present study, polarized Raman microspectroscopic and imaging analyses were used to elucidate collagen fibril orientation at various levels of structure in native rat tail tendon under mechanical load. In situ humidity-controlled uniaxial tensile tests have been performed concurrently with Raman confocal microscopy to evaluate strain-induced chemical and structural changes of collagen in tendon. The methodology is based on the sensitivity of specific Raman scattering bands (associated with distinct molecular vibrations, such as the amide I) to the orientation and the polarization direction of the incident laser light. Our results, based on the changing intensity of Raman lines as a function of orientation and polarization, support a model where the crimp and gap regions of collagen hierarchical structure are straightened at the tissue and molecular level, respectively. However, the lack of measurable changes in Raman peak positions throughout the whole range of strains investigated indicates that no significant changes of the collagen backbone occurs with tensing and suggests that deformation is rather redistributed through other levels of the hierarchical structure.
Journal of Applied Biomedicine
The aim of our work was to prepare part of the input data for a computational biomechanical model of both the active and passive elements of the tunica media of an aortic aneurysm. We analyzed tissue samples of the anterior wall of the normal, atherosclerotic and aneurysmatic subrenal abdominal aorta. We assessed the proportions of smooth muscle cells, elastin and collagen in histological sections of these samples and studied the morphological characteristics of the elastin network in the tunica media. Selected photomicrographs were studied, representing relatively well preserved areas without artifacts, ruptures, corrupted integrity of the tunica media or total elastinolysis. A new method was introduced for the assessment of structures formed by elastin membranes and fibres, using the fast Fourier transform (FFT) technique. The image was transformed into reciprocal (Fourier) space and the method made use of the fact that the FFT was very sensitive to the orientation distribution of thresholded elastin morphology. The results of this comparative study, obtained from selected samples from 24 patients, revealed that the percentage values of the constituents of the arterial wall can not distinguish between the preserved segments of normal, atherosclerotic or aneurysmatic aorta. The results of the Fourier analysis proved that the FFT provided an efficient method for evaluating cross sections of the elastin membranes and fibres, reflecting their anisotropy. The shape of the power spectrum of elastin was a simple pattern, whose description was quantified by the shape of its polar coordinates histogram. We discuss the methodological difficulties and biomechanical implications of our work as well compare it to other methods of elastin analysis.
Characterisation of elastin and collagen in aortic bioprostheses
Medical & Biological Engineering & Computing, 2000
Porcine aortic valves used as cardiac valve bioprostheses are well adapted to physiological functions in the short term, but they lack long-term durability. Several multi-step extractions have been performed to obtain a perfectly acellular matrix. A new physical methodology is proposed to evaluate the resulting fibrous protein damage after biochemical extraction (TRI-COL and SDS). Thermal analysis techniques are adapted to collagen and elastin characterisation in the solid state. The aortic tissue thermal transitions are determined by differential scanning calorimetry (DSC): elastin glass transition is observed around 200°C, and collagen denaturation is observed around 230 ° C. These parameters are characteristic of the elastin network arrangement and of collagen triple-helix stability. The technique of thermostimulated currents (TSC) is well suited to specify the chain dynamics of proteins. The lowtemperature relaxations observed in both collagen and elastin are associated with Iocalised motions, whereas the high-temperature modes are attributed to more delocalised motions of the chains. Therefore TSC and DSC spectrometries allow physical parameters specific to collagen and elastin to be obtained and their interaction in aortic tissues to be determined. According to the significant evolution of these parameters on SDS samples, the destabilising effect of this detergent is highlighted.
Raman study of the shockwave effect on collagens
Spectrochimica Acta Part A-molecular and Biomolecular Spectroscopy
The Raman spectra (1800-200 cm −1 ) of isolated dried collagen types I and III were recorded at different times after shockwave (SW) application in aqueous media. SWs were applied in a single session. One week after the SW application the vibrational data analysis indicates changes in the conformation of the collagens; orientational changes are also inferred. During the next three weeks collagens tended to recover the conformation and orientation existing before SW application.