Name: using digital image correlation to characterize local strains on vascular tissue specimens
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注：下述程序进行的，在南卡罗来纳大学哥伦比亚，南卡罗来纳州批准的机构动物护理和使用委员会的协议的一部分。 1.组织收购和解剖<ol><li>消毒前，组织剥离所有的外科手术工具。高压釜外科剪刀和细标准钳子以及15 psi的压力和121℃温度下15分钟下外科刀片。 </li><li>获取一组新鲜猪（7个月大的长白男性，60-70公斤）的肾脏具有完整主动脉从本地屠宰场。运输组织返回到冰水1％的磷酸盐...

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尽管以前的研究已经使用了范围广泛的染料跟踪视频的方法来评估样本的应变18,20,21,23,24，我们现在的目标是提供一个全面的方法来夫妇单轴拉伸试验与2D-DIC的评估表面菌株对血管组织样品。具有高分辨率摄像机和内部图像分析软件，应变场可以在预定的表面区域内测量样品经历单轴加载。特别是血管组织的机械测试的相关性，所提出的技术可直接适用于评估平面双轴测试，从而能够识别...

研究丰富的历史跨度超过50年一直专注于量化血管组织的力学性能。这些研究使我们更好地理解这两种生理和病理血管行为，评价血管内装置的功效/相容性，并有助于在设计和工程化的血管的制造构建1-6提供了基础。软组织和它们的机械性能的构模拟的机械响应的精确测量固有地由于机械异质性，各向异性，和非线性大多数组织类型呈现挑战。此外，实验测量往往是由在样品握接口在机械测试的过程中引入本地复杂性（即，弯曲，摩擦，应力集中，撕裂）和机械性能的不可避免的过渡一旦组织被从活的动物切除混淆。 &lt;/ P&gt; 甲单轴拉伸实验是，可以在由固体材料制成的试样进行的最简单的机械试验中，并且通常被用来评估血管组织的机械响应。这些实验的结果提供对本地和工程化的组织来源有用的初步信息，并可以用来比较对血管壁7-11的力学行为的某些治疗，疾病状态，或药理学化合物的影响。 典型地样品上具有相对均匀的几何形状，这是最常见的狗骨或环状7,8,12-14软组织的单轴机械测试。然而，从这些理想化的几何形状显著出发，可能会发生由于与组织解剖，分离，并且测试系统内的夹紧相关的挑战。任何非均匀性的几何形状将最终引起异构应力和应变字段当样品进行单轴延伸，与异质取决于实际样品的形状，以及样本大小（相对于夹具）与材料9,15,16的机械性能的程度。当字段非均质性是显著，根据相对的抓握姿势样品应变的计算是不准确的，因此，以评估机械性能不足的基础。 视频分析系统已被广泛用于软组织应变测量，通常使用施加在试样表面17,18高对比染料标记。数字图像相关，光学计量技术，该技术通过变形之前和之后在试样的表面比较灰度强度值测量全视野表面应变，已经与视频一起使用的软组织19-21分析。相比interferometr有数字图像相关的几个优点集成电路的方法可用于测量。首先，作为以非接触测量技术，它最大限度地减少修改由于在该测量系统的影响的检体的方式的材料性质的混杂影响。第二，它需要一个更严格的测定环境，并具有较宽范围的灵敏度和分辨率比其它方法的。第三，赋有摄像视一个全视场的能力，这种技术可以表征的平均及本地机械响应。对于该方法的详细说明，我们鼓励读者通过萨顿22看的书。 以获得在试样表面的应变场，一个二维数字图像相关技术（2D-DIC）都可以使用。简言之，样品的图像被捕获在卸载和装载各种状态。第一图像被划分为称为子集（M×M像素）的小方块形成网状用于随后的计算2D应变场。使用图像匹配算法得到的变形样品每平方米的位置。每个正方形的运动，然后追踪，图像逐图像，得到随后可用于通过各种方法，包括多项式拟合或有限元插值导出变形梯度和菌株位移字段。在本手稿中，我们提供了通过整合单轴拉伸试验和2D-DIC评估原生血管组织表面应变场的详细方法。

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			<td height="42" style="height:42px;width:216px;">Uniaxial tensile mechanical tester</td>
			<td style="width:176px;">Enduratec</td>
			<td style="width:119px;">3230 AT/HR</td>
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			<td height="126" style="height:126px;width:216px;">Blue tissue marking dye</td>
			<td style="width:176px;">http://www.ebay.com/itm/Tissue-Marking-Dye-in-Bottles-2oz-Bottle-1-ea-/201193551510?pt=LH_DefaultDomain_0&#38;hash=item2ed811f696</td>
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			<td height="21" style="height:21px;width:216px;">Sprayer</td>
			<td style="width:176px;">Anest-iwata</td>
			<td>CM-B</td>
			<td>Custom Micron B</td>
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			<td height="21" style="height:21px;width:216px;">Camera</td>
			<td style="width:176px;">Point Grey</td>
			<td style="width:119px;">GS2-GE-50S5M-C</td>
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			<td height="21" style="height:21px;width:216px;">Lens</td>
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			<td height="21" style="height:21px;width:216px;">Vascular tissue</td>
			<td style="width:176px;">Caughman Inc</td>
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			<td height="42" style="height:42px;width:216px;">0.9% Sodium Chloride Injection PBS</td>
			<td style="width:176px;">BAXTER HEALTHCARE CORP.</td>
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			<td height="21" style="height:21px;width:216px;">Wintest 4.1</td>
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			<td height="21" style="height:21px;width:216px;">Tissue adhesive</td>
			<td style="width:176px;">&#160;3M Vetbond&#160;</td>
			<td style="width:119px;">1469SB</td>
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			<td height="21" style="height:21px;width:216px;">Disinfectant&#160;</td>
			<td style="width:176px;">Fisher Scientific</td>
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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.

从血管组织倾斜的单轴拉伸试验获得的机械数据由负载与在给定的位移速率应用的样本位移关系。在这项研究中，2D-DIC与单轴机械测试结合用于测量在以各种变形的状态正交的方向的样品表面应变场。血管组织的粘弹性性质是通过在之前机械预处理负载 - 位移曲线的显着程度的​​滞后表现。以促进机械测试的再现性，将获得的弹性机械响应，所述组织是通过几个装载-卸...

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

利用数字图像相关表征的血管组织标本本地菌株

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.

Research

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