Name: investigating stress-relaxation and failure responses in the trachea
Uploaded: 2022-10-18T12:30:00
Description: Watch this Scientific Journal Video about Investigating Stress-relaxation and Failure Responses in the Trachea at JoVE.com

Research reported in this publication was supported by the Eunice Kennedy Shriver National Institute of Child Health and Human Development of the National Institutes of Health under Award Number R15HD093024 and the National Science Foundation CAREER Award Number 1752513.

All methods described were approved by the Institutional Animal Care and Use Committee (IACUC) at Drexel University. All cadaveric animals were acquired from a United States Department of Agriculture (USDA)-approved farm located in Pennsylvania, USA. A cadaver of a male Yorkshire pig (3 weeks old) was used for the present study.
1. Tissue harvest
<ol>
	<li>Acquire a cadaver of a pig from an approved farm and perform the experiments within 2 h from euthanasia. Keep the cadave...

<ol>
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Very few studies have reported the stress-relaxation properties of the trachea21,23. Studies are needed to further strengthen our understanding of the time-dependent responses of the tracheal tissue. This study offers detailed steps to perform such investigations; however, the following critical steps within the protocol must be ensured for reliable testing: (1) proper tissue hydration, (2) similar tissue-type (number of cartilaginous rings and muscle) distributi...

Despite its critical role in pulmonary disease, the largest airway structure, the trachea, has limited studies detailing its viscoelastic properties1. An in-depth understanding of the time-dependent, viscoelastic behavior of the trachea is critical to pulmonary mechanics research since understanding the airway-specific material properties can help advance the science of injury prevention, diagnosis, and clinical intervention for pulmonary diseases, which are the third leading cause of death in the United States2,3,4.
Available tissue characterization studies have reported the stiffness properties of the trachea5,6,7,8. The time-dependent mechanical responses have been minimally investigated despite their importance in tissue remodeling, which is also altered by pathology9,10. Moreover, the lack of time-dependent response data also limits the predictive capabilities of the pulmonary mechanics computational models that currently resort to using the generic constitutive laws. There is a need to address this gap by performing stress-relaxation studies that can provide the required material characteristics to inform biophysical studies of the trachea. The current study offers details of testing methods, data acquisition, and data analyses to investigate the stress-relaxation behavior of the porcine trachea.

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			<td>eXpert 7600</td>
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investigating stress-relaxation and failure responses in the trachea

The biomechanical properties of the trachea directly affect the airflow and contribute to the biological function of the respiratory system. Understanding these properties is critical to understanding the injury mechanism in this tissue. This protocol describes an experimental approach to study the stress-relaxation behavior of porcine trachea that were pre-stretched to 0% or 10% strain for 300 s, followed by mechanical tensile loading until failure. This study provides details of the experimental design, data acquisition, analyses, and preliminary results from the porcine tracheae biomechanical testing. Using the detailed steps provided in this protocol and the data analysis MATLAB code, future studies can investigate the time-dependent viscoelastic behavior of trachea tissue, which is critical to understanding its biomechanical responses during physiological, pathological, and traumatic conditions. Furthermore, in-depth studies of the biomechanical behavior of the trachea will critically aid in improving the design of related medical devices such as endotracheal implants that are widely used during surgeries.

Figure 1 shows the failed tissue near the clamping site and the presence of tissue within the clamp, confirming no slip during tensile testing. Figure 2 indicates various failure sites, including the top or bottom clamping sites or along the length of the tissue, that were observed during tensile testing among the tested samples. Data analysis results are summarized in Figures 3-4 and Tables...

Watch this Scientific Journal Video about Investigating Stress-relaxation and Failure Responses in the Trachea at JoVE.com

Investigating Stress-relaxation and Failure Responses in the Trachea

The present protocol determines the tensile stress-relaxation and failure properties of porcine tracheae. Results from such methods can help improve the understanding of the viscoelastic and failure thresholds of the trachea and help advance the capabilities of computational models of the pulmonary system.

The biomechanical properties of the trachea directly affect the airflow and contribute to the biological function of the respiratory system. Understanding ...

This protocol offers a detailed approach to investigating the stress-relaxation responses of the trachea. Investigating the stress-relaxation responses of the trachea is critical to the understanding of pulmonary mechanics research. To begin, make a vertical midline incision along the neck of the cadaver and expose the thyroid cartilage, cricoid cartilage, and trachea from the hyoid bone to the suprasternal notch.Harvest the larynx and the full length trachea using a 10 number blade. Separate the trachea sample from the larynx and then cut the tracheal tube longitudinally along the entire length on one side using the blade. Cut the trachea into two circumferential strips approximately five millimeter wide proximally and two longitudinal strips approximately five millimeter wide distally with the minimum length of these strips being 25 millimeters.Navigate to the downloaded zipped folder, then extract its contents and navigate to the Failure Only folder. Store data from tested samples in a Microsoft Excel file using the mm/dd/yy file naming convention. Open the sample file tested on April 30th, 2022 in the Failure Only folder and recognize the multiple worksheet tabs containing the raw data from each sample subjected to mechanical failure on this particular date.Ensure the samples are labeled using the sample type, sample number, and pre-stretch strain level percentage file convention. Select the worksheet tab TA_1_0%Ensure that the raw data header columns are labeled as described in the text manuscript and close the current Microsoft Excel file, then return to the working directory of the data analysis software and navigate to the relaxation folder. Store data from the experimental group samples tested on a particular date in a Microsoft Excel file as demonstrated earlier.Open the relaxation folder and recognize the multiple worksheet tabs containing the raw load relaxation data from each sample in the experimental group tested on that particular date. Pause and note that each of the samples was subjected to mechanical failure under tensile mechanical loading as indicated by the worksheet tabs included in this Microsoft Excel file. Ensure that raw load relaxation data for each sample indicated by any worksheet tab are formatted correctly, then save and close the current Microsoft Excel file.Return to the working directory of the data analysis software and navigate to the folder failure post-relaxation. Confirm that there is a Microsoft Excel file with the same date as in the relaxation folder. Open the Excel file in the failure post-relaxation folder and recognize multiple worksheet tabs each containing raw mechanical failure data from the same samples present in the relaxation folder.Ensure that each sample's header column for the raw mechanical failure data is formatted correctly. Close the current Microsoft Excel file and return to the working directory of the data analysis software. Open the Microsoft Excel file testingDates.xlsx which will direct the code to analyze user-specified testing dates. List testing dates in the first column in the mm/dd/yy format. In the second column, indicate using a Y or N whether the samples on the testing date were from the experimental group which includes stress-relaxation followed by mechanical failure.In the third column, indicate whether any samples were from the control group showing direct mechanical failure. Save and close the current Microsoft Excel file and return to the working directory of the data analysis software, then open the main script file main_relax_failure. m, select the large green arrow on the software interface to run the code.Alternatively, type run main calc relax in the command window. Upon being prompted, input comma-separated fixed elongation levels in percentage for the various experimental groups and press OK, then input comma-separated stress-relaxation testing durations in seconds for the various experimental groups and press OK.Once the code is successfully run, ensure that the computed results are available in the working directory of the data analysis software as a Microsoft Excel file with mm/dd/yy replaced by the date on which the code was run. Stress-relaxation responses for tracheal samples following axial or circumferential pre-stretch to 10%strain demonstrated an initial peak in the stress load, followed by a percentage reduction in stress over the 300-second hold.The stress-strain responses of the tracheal sample subjected to failure testing under axial or circumferential loads following no pre-stretch or 10%pre-stretch indicated failure stress. The preliminary tests successfully characterized the stress-relaxation responses of the tracheal tissue wherein the initial peak stress was higher in axial loading directions. In contrast, the percentage reduction in stress was higher in the circumferential loading direction when compared to the axial loading direction.The relaxation times were also higher in the axial loading direction than the circumferential loading direction for the same 10%pre-stretch group. In the failure data, the failure stress and e-values were higher in circumferential loading directions in the zero and 10%pre-stretch groups, whereas the failure strain reported in the axial loading directions was higher. Ensure that the tested sample data is labeled correctly and the header columns of the data sheets are formatted correctly.These steps are critical to run the data analysis code. In addition to the acute, a chronic stress-relaxation response can also be studied. Also, a quasi-static stress-relaxation response can be investigated.

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