Name: using digital image correlation to characterize local strains on vascular tissue specimens
Uploaded: 2016-01-24T14:00:00
Description: Watch this Scientific Journal Video about Using Digital Image Correlation to Characterize Local Strains on Vascular Tissue Specimens at JoVE.com

Le logiciel et le support technique étaient une gracieuseté de corrélée Solutions Incorporated (www.correlatedsolutions.com).

REMARQUE: Les procédures décrites ci-dessous ont été réalisées dans le cadre d&#39;un protocole approuvé par le Comité de protection des animaux et l&#39;utilisation institutionnelle à l&#39;Université de la Caroline du Sud à Columbia, Caroline du Sud. 1. Acquisition et tissus Dissection <ol><li> Stériliser tous les instruments chirurgicaux avant la dissection du tissu. Des ciseaux et des pinces chirurgicales autoclave standard fines ainsi que les lames chirurgicales sous pression de 15 psi et la t...

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Bien que des études antérieures ont utilisé un large éventail de méthodes de vidéo colorant de suivi pour évaluer la souche de l&#39;échantillon 18,20,21,23,24, notre objectif actuel est de fournir une méthodologie globale pour essai de traction uniaxiale de couple avec 2D-DIC pour l&#39;évaluation des souches de surface sur des échantillons de tissus vasculaires. Avec un appareil photo de haute résolution et un logiciel maison-analyse d&#39;image, le champ de déformation peut être mesurée dans...

Un riche histoire de la recherche couvrant plus de 50 ans a été axée sur la quantification des propriétés mécaniques des tissus vasculaires. Ces études nous permettent de mieux comprendre à la fois le comportement physiologique et pathologique de vaisseaux sanguins, de fournir une base pour évaluer l&#39;efficacité / compatibilité des dispositifs endovasculaires, et l&#39;aide à la conception et la fabrication de l&#39;ingénierie vasculaire construit 1-6. La mesure précise de la réponse mécanique des tissus mous et la modélisation du comportement de leurs propriétés mécaniques est intrinsèquement difficile en raison de l&#39;hétérogénéité mécanique, anisotropie, et la non-linéarité présentée par la plupart des types de tissus. En outre, des mesures expérimentales sont souvent confondus par les complexités locales introduites au niveau des interfaces échantillon grip dans le cadre d&#39;essais mécaniques (c.-à-flexion, la friction, les concentrations de contraintes, larmoiement) et la transition inévitable de propriétés mécaniques, une fois le tissu est excisé de l&#39;animal vivant. &lt;/ p&gt; Un essai de traction uniaxiale est parmi les plus simples essais mécaniques qui peuvent être effectuées sur un échantillon constitué d&#39;un matériau solide, et est souvent utilisé pour évaluer la réponse mécanique du tissu vasculaire. Les résultats de ces expériences fournissent des informations préliminaires utiles pour les deux sources de tissus natifs et d&#39;ingénierie, et peuvent être utilisés pour comparer les effets de certains traitements, états pathologiques ou des composés pharmacologiques sur le comportement mécanique de la paroi vasculaire 7-11. Essais mécaniques uniaxiale des tissus mous est généralement effectuée sur des échantillons avec des géométries relativement uniformes, qui sont le plus souvent d&#39;os de chien ou en forme de 7,8,12-14 anneau. Cependant, départ significatif de ces géométries idéalisés peut se produire en raison des défis associés à la dissection des tissus, l&#39;isolation et serrage au sein du système de test. Toute non-uniformité dans la géométrie sera finalement donner lieu à un stress hétérogène et souchechamps lorsque l&#39;échantillon est soumis à l&#39;extension uni-axiale, avec le degré d&#39;hétérogénéité dépend de forme réelle de l&#39;échantillon, ainsi que la taille de l&#39;échantillon (par rapport aux pinces) et les propriétés mécaniques du matériau 9,15,16. Lorsque hétérogénéités de champ sont importantes, les calculs de déformation de l&#39;échantillon sur la base des positions relatives d&#39;adhérence sont inexactes et donc une base insuffisante pour évaluer le comportement mécanique. Systèmes d&#39;analyse vidéo ont été largement utilisés pour les mesures de déformation des tissus mous, souvent en utilisant des marqueurs de colorant à contraste élevé appliqué à la surface de l&#39;échantillon 17,18. Corrélation d&#39;image numérique, une technique métrologique optique qui mesure la tension de surface plein champ en comparant les valeurs de gris d&#39;intensité de niveau de la surface de l&#39;échantillon avant et après déformation, a été utilisé en conjonction avec l&#39;analyse vidéo de tissus mous 19-21. Il existe plusieurs avantages de corrélation d&#39;images numériques par rapport à interferometric méthodes qui peuvent être utilisées pour les mesures. Tout d&#39;abord, comme une technique de mesure sans contact, il minimise les effets de confusion de la modification des propriétés des matériaux due à la manière dont le système de mesure affecte le spécimen. Deuxièmement, il nécessite un environnement beaucoup moins sévères de mesure et a une plus large gamme de sensibilité et de la résolution que les autres méthodes. Troisièmement, doté de la capacité de capturer un champ de vision, cette technique peut caractériser à la fois la moyenne et les réponses mécaniques locales. Pour une explication détaillée de la méthode, les lecteurs sont encouragés à voir le livre de Sutton 22. Pour obtenir des champs de contrainte sur la surface de l&#39;échantillon, une technique de corrélation d&#39;image numérique bidimensionnelle (2D-DIC) peut être utilisé. En bref, des images de l&#39;échantillon sont capturées à états chargés déchargé et divers. La première image est divisée en sous-ensembles appelés petits carrés (M × M pixels) qui forment un maillage pour le calcul subséquent deDe champs de contraintes 2D. La position de chaque carré dans l&#39;échantillon déformé est obtenu en utilisant un algorithme image correspondante. Le mouvement de chaque carré est ensuite suivi, image par image, ce qui donne champs de déplacement qui peuvent ensuite être utilisées pour calculer des gradients de déformation et les souches par une variété de méthodes, y compris polynôme montage ou éléments finis interpolation. Dans le présent manuscrit, nous proposons une méthodologie détaillée pour l&#39;évaluation des champs de déformation de surface sur les tissus vasculaires indigènes grâce à l&#39;intégration des essais de traction uniaxiale et 2D-DIC.

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using digital image correlation to characterize local strains on vascular tissue specimens

Characterization of the mechanical behavior of biological and engineered soft tissues is a central component of fundamental biomedical research and product development. Stress-strain relationships are typically obtained from mechanical testing data to enable comparative assessment among samples and in some cases identification of constitutive mechanical properties. However, errors may be introduced through the use of average strain measures, as significant heterogeneity in the strain field may result from geometrical non-uniformity of the sample and stress concentrations induced by mounting/gripping of soft tissues within the test system. When strain field heterogeneity is significant, accurate assessment of the sample mechanical response requires measurement of local strains. This study demonstrates a novel biomechanical testing protocol for calculating local surface strains using a mechanical testing device coupled with a high resolution camera and a digital image correlation technique. A series of sample surface images are acquired and then analyzed to quantify the local surface strain of a vascular tissue specimen subjected to ramped uniaxial loading. This approach can improve accuracy in experimental vascular biomechanics and has potential for broader use among other native soft tissues, engineered soft tissues, and soft hydrogel/polymeric materials. In the video, we demonstrate how to set up the system components and perform a complete experiment on native vascular tissue.

Les données mécaniques acquises lors d&#39;un essai d&#39;extension uniaxiale rampe sur le tissu vasculaire se compose de charge en fonction de relations appliquées échantillon de déplacement à une vitesse de déplacement donné. Dans cette étude, 2D-DIC en conjonction avec les essais mécaniques uniaxiale est utilisé pour mesurer les champs de l&#39;échantillon dans des directions orthogonales à différents états déformés de déformation de surface. La nature viscoélastiqu...

Watch this Scientific Journal Video about Using Digital Image Correlation to Characterize Local Strains on Vascular Tissue Specimens at JoVE.com

Using Digital Image Correlation to Characterize Local Strains on Vascular Tissue Specimens

Utilisation de corrélation d&#39;images à caractériser les souches locales sur des échantillons de tissus vasculaires

We describe the use of digital image correlation to characterize the local surface strain field on vascular tissue samples subjected to uniaxial tensile testing. These measurements facilitate precise quantification of the sample mechanical response and the generation of constitutive stress-strain relations.

Characterization of the mechanical behavior of biological and engineered soft tissues is a central component of fundamental biomedical research and ...

The overall goal of this protocol is to characterize the local surface strain field on vascular tissue samples. This is accomplished using a digital image correlation technique with uniaxial tensile testing. This method can help answer key questions in the field of soft tissue mechanics and specifically provide information to identify and invalidate increasingly sophisticated computational and mathematical models of vascular tissue.The main advantage of this technique that facilitates precise quantification of a strain field heterogeinity on the sample surface, which is a function of inherent material properties, symbol geometry and employed testing modality. As soon as the tissue arrives at the lab, isolate the abdominal aorta from surrounding tissue using surgical scissors and forceps. Then, wash the vessel three times using a syringe filled with PBS.Following the washes, use scissors and forceps to remove as much perivascular tissue as possible, without compromising the integrity of the sample. Then, onto the middle section of the vessel, position a sharp razor blade, perpendicular to the vessel's longitudinal axis and chop the vessel three times to make two ring samples. Next, position a blade onto one of the rings to make a radial cut.Firmly slice the ring to make a strip shaped sample for uniaxial mechanical testing. Do this to both rings. Temporarily store the two samples in a 100 mm glass petri dish submerged in PBS.To speckle the sample surface have an air brush ready to spray tissue marking dye. Connect the air brush to a pressure valve set to produce 100 psi. Next, add the tissue marking dye.The nozzle diameter must be calibrated for speckle diameters between 60 and 100 microns. Then, spray tissue marking dye on the intimal surface of the sample for approximately five seconds. Do this three times to ensure that the speckle pattern uniformly covers the sample surface.To begin, mount the sample to the testing apparatus. First, attach each end of the sample to a plastic strip using a tissue adhesive. Place plastic on both the top and bottom of the sample with the adhesive, making a sandwich.Place the sample flat on a tissue cutting board then measure it's dimensions using a digital caliper. Next, initiate the system controls for the test apparatus. On the system control's home screen, select waveform on the task bar located on the set up tab.Then, adjust the position of the upper grip of the mechanical tester to negative four mm to provide a 4 mm extension relative to the designated initial position in the system. Now, gently secure one plastic strip into the upper grip of the mechanical tester and allow the sample to hang freely. Next, adjust the position of the lower grip so that the free end of the sample can be secured without extension.Then, gently secure the plastic strip attached to the free end, into the lower grip of the tester. With the sample mounted, zero the system load cell. Then measure the length of the sample and use this as the reference length when calculating global circumferential strains.Now, in the software control, enter the mechanical testing protocol. Here, four uniaxial displacement cycles are applied. Each cycle extends the sample length by 18 percent at a displacement rate of 0.01 mm per second.To document the test, take a photo every few seconds. Position a camera 1.5 m from the loading frame, perpendicular to the sample and focus it on the sample. In the image capture software, in the option select system"select PGR2, then set the project path to save the images to be analyzed.Click the time square icon and specify the acquisition interval as 5 seconds. Now, import the image obtained. Zoom in on an individual speckle and then count the number of pixels within this individual speckle.After verifying the quality of the speckle pattern, simultaneously click the run"icon in the system and the start"icon in the image capture software to start the test. Throughout the protocol, intermittently spray PBS on the sample so it does not dry out. However, do this whenever it is in the unloaded state not during data acquisition.After opening the image analysis software, click the speckle images"tab and select all images which need to be analyzed. Then, click on the rectangle tool and select the area of interest in the first image. Next, enter a 31 by 31 pixel subset size and a step size of five pixels.Now click the start analysis"tab in the software and set the interpolation to be an optimized 8 trap. Also, set the criterion as zero normalized square differences and the subset weights option as Gaucian. Check the threshold options.They should be on the default. Next, click on the post processing sub tab under the start analysis tab. Select the option, string computation"and leave filter size and type of filter as the default.Set the tensor type to Lagrange. Finally, select the data tab and then select an analyzed image to visualize the surface strain field. 2D DIC in conjunction with uniaxial mechanical testing, was used to measure the surface strain field of a vascular tissue specimen, at various deformed states.The viscoelastic nature of the tissue was notable by the degree of hysteresis in the low displacement curves prior to the mechanical preconditioning. However, with preconditioning, the hysteresis was gradually diminished. As expected, the local circumferential strain values increased with applied sample displacement.Circumferential strain was generally less near the center of the sample as compared to near the sample grip interface. In the longitudinal direction, the resultant, non-uniform compressive strain on the sample intimal surface increased as the sample was gradually extended. The color changes within the contours for the full field strain measurements, clearly show the high heterogeneous nature of the aorta when subjected to nominally, uniaxial tensile loading.The coefficients of variation of the surface strain fields in orthogonal directions were then calculated in each experimental state. The variation in the surface strain was found to have an inverse relationship with the samples extension. The high level of heterogeneity in the material response is quantified in the table by the coefficent of variation, or CV.After watching this video, you should have good understanding of how to quantify the local surface mechanical response using digital image correlation coupled with uniaxial tensile testing of vascular tissue samples.After it's development, this technique paved the way for researchers in the field of soft tissue mechanics to explore physiological, pathological and modulated mechanical response of vascular tissue.

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