Investigating Stress-relaxation and Failure Responses in the Trachea

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.