• Specifications
• ExperimentationTissueMechanics

/Discussion

Infrastructure

• Infrastructure/TissueCharacterization

Tissue Types

Previous Protocols

• Specifications/Specimen

Data Analysis

• Refer to this page for all Tissue Testing Python scripts.

Protocols

Skin

Experimental strains and strain rates were chosen based on surgical tools data (see SurgTools_SkinSurfaceStrain.pdf).

Experiment Conditions

Multi-step tensile test at room temperature to characterize sample stress-strain. After following this protocol for up to four tests, the test should provide repeatable results.

Measurements

• Force-displacement data (unfiltered @ 2.5 KHz unless downsampled)
• Video data (RAW format, 640x480 @ 10 Hz unless downsampled)

Machine Preparation

1. Power on the motion controller and open Mach-1 Motion software.
2. Calibrate the 10kg load cell according to the prompts on the Load Cell menu.
   1. Clamp details can be found on Infrastructure page.

Sample Preparation

1. Refer to this page for instructions on obtaining bulk sample. Only handle one sample at a time.

2. Hydrate the sample using a saline spray bottle after removing from freezer. Let the sample thaw to room temperature for about an hour before testing.
3. Use a scalpel to cut along the long edge of the rectangular sample. Measure 6 mm for the width and trim the ends so that the gage length is 25-30 mm.
4. Place sample on a saline soaked paper towel while clamps are prepared, keeping orientation in mind.
   1. Remember to keep the skin sample hydrated and at room temperature or below.

Test Preparation

1. Calibrate 10kg load cell.
2. Set up the machine for a tensile test**.
3. For zeroing position.
   1. Place the complementary puzzle pieces of the clamp in machine and align the clamp heads (not overlapping or touching , align them one behind the other). Use the camera to view the clamps along the Y axis to ensure there is minimal space between the two clamps.
   2. Set Z direction displacement to zero.

      • Note: The positive Z direction is towards the base of the machine.

      • Note: This step sets the zero position of the system using which starting length of the specimen is determined.

4. After the Mach-1 is zeroed with clamps, remove clamps for tissue placement. Create a z-direction displacement of roughly 20mm so that the clamped sample can be placed.
5. Use one drop of tissue adhesive on the clamps before placing the tissue, as well as a drop of adhesive on the tissue before placing the other half of the clamp. Secure screws completely to prevent slip.
   1. Secure tissue in clamps such that the entire breadth of the clamp is used and sample is aligned with Z axis.
6. Slide secured, clamped tissue into the complimentary pieces on the Mach-1 with some slack.
7. Align the sample in the X and Y directions and set displacements to zero using the Manual Controls. Use the camera to align the specimen along the Y axis.
8. Set up a ruler to calibrate the image of the sample to find its width at its reference lengths.

Thickness Measurement

1. Set up a camera level to the sample in the XZ plane. Place a ruler for calibration next to the sample in the same plane to later capture images during the "Wait" functions. The image will be used to measure thickness at its reference lengths using this script to automatically or manually segment the image.

Testing Procedure

Tensile test

1. Set default location to a folder for the data.txt file, naming the folder after the sample name.
2. Set the Mach1 camera's frame interval to 10 seconds.
3. Determine Reference Length

   • Use force filter.

   • For tensile tests the 'initial length' protocol (programmed in Mach1) is performed first to obtain the initial length of the sample.
   • Create sequence in Mach 1 Analysis software with the following steps:
     1. Zero Load
     2. Find Contact
     3. Direction: Negative ; Stage Velocity: 0.05 mm/s ; Contact Criteria: 25 gf ; Stage Limit: 4.0 mm ; Stage Repositioning: Stop Criteria + Offset

     4. Wait: 60 seconds. Record displacement as reference length, it will be a negative value.

     5. Move Relative: Unload by 2mm
     6. Record the displacement during the "Wait" function as the first reference length of the sample.

   • Enter the reference length into this script to calculate displacements during the test.

4. Testing

   1. Do not use force filter.

   2. The protocol for tensile preconditioning is programmed in the system and can be run with adjustments based on sample dimensions.
   3. Move Absolute: Compress the sample by 2% of the reference length at 1.00mm mm/s to capture the full loading profile of the specimen.

   4. Move Relative: max strain % (+ 2% of the reference length) nominal strain at 20%/s

   5. Move Relative: -max strain % nominal strain at 20%/s

   6. Move Relative: to load sample (max strain - 2.5% nominal strain)

   7. Sinusoidal: preconditioning with an amplitude of 2.5% strain for 1000 cycles at 2 Hz.

   8. Move Relative: to unload sample (max strain - 2.5% nominal strain)

   9. Move Relative: Unload completely by 2mm.
5. Repeat the Determine Reference Length step to find the reference length after preconditioning.

   • Use force filter.

   • Enter the second reference length into the prompt from the tension_pc.py script.
6. Complete the ramp after preconditioning
   1. Move Absolute: Compress the sample by 2% of the reference length at 1.00 mm/s to capture the full loading profile of the specimen.

   1. Move Relative: max strain % (+ 2% of the reference length) nominal strain at 20%/s

   2. Move Relative: -max strain % nominal strain at 20%/s

   3. Move Relative: Unload completely by 2 mm.

Post Tensile Test

1. Quickly examine the data by opening the Mach-1 Analysis software to ensure that the general shape of the curves make sense. This is to check that there were no major errors during the test. Examples of fatal test errors include mistakes in sequence entry that cause the machine to move in the wrong direction, major slippage of the specimen in the clamps, or a tear in the sample.
2. Rename the data.txt file according to proper naming convention.
3. Carefully remove the sample by its clamps, keeping some slack in the sample.
4. Store the sample in a saline soaked paper towel and place into sealed plastic bag.
   • Be sure to note the orientation of the sample.
5. Wait at least 24 hours before repeating the test to allow the sample to recover.
6. Repeat the test, beginning from 5.2.3.

   • Do not move the machine to 'zero' the Z displacement when performing sequential tests.

7. After the tests are completed, fill in the xml document. Run the script from the command prompt with the xml document as the argument to structure the data in a usable way. Then, run the plot script to open the following windows:

   • A figure for each .txt file that represents load-time for preconditioning
   • A figure for each .txt file that includes load-time and displacement-time over the entire test, not including the preconditioning
   • A figure for each .txt file that displays load-time and displacement-time
   • A figure for that combines each test to include force-displacement and stress-strain curves

8. Seethis page for results discussion.

Fat

Experiment Conditions

Unconfined compression test to obtain force displacement data from the samples.

Measurements

Force-displacement data (unfiltered @ 2.5 kHz unless downsampled) Video data (RAW format, 640x480 @ 10 Hz unless downsampled)

Operating Procedures

Sample preparation

Thickness measurement

• Once the samples are punched out, measure the thickness using the optical thickness measurement system (OTMS).

Test set up

Unconfined compression test

• Calibrate the load cell before the test.
• Place the sample on a flat compression platform and fix the whole assembly in a saline bath.
• Test is done at room temperature.
• Current sample size 7mm high (9mm radius)

Testing

Unconfined Compression test

• Thickness obtained from OTMS is used to calculate required strains and strain measurements.

• To find the initial position to begin testing use 'find contact' protocol.

• Use force filter.

• Preload to 0.3 gf at a loading rate of 0.005 mm/s
• Wait: 1 min.
• Note the position.
• Unload by 1mm

2. Unconfined Compression Test

• Do not use force filter

• Use compression preconditioning protocol.
• Move Absolute: to bring sample to the reference initial position @ 0.005 mm/s
• Move Relative: to load sample (by 7.5% nominal strain)
• Sinusoidal: preconditioning with an amplitude of 7.5% strain for 1000 cycles at 2 Hz.
• Move Relative: to unload sample (by 7.5% nominal strain)
• Unload completely by 1mm.

• Make sure for each step of the test sequences the location of file is appropriately selected.
• All data is stored in data.txt file in a main data folder. After the test is complete move this file to appropriate folder with the right specimen name. For naming convention go to Specifications/DataManagement
• Maintain a readme.txt file in the specimen master specimen folder to note down any relevant information for all the tests performed for the specimen.

Data analysis

• Once the test is complete, the acquired data is reviewed using the Mach1 Analysis software. The test should be repeated if necessary.
• The data can be loaded and visualized in the analysis software, and if the rates and duration for which the rate is applied are as expected, the data will pass the check. Alternatively, the data can be run through the analysis python script to assess the data quality more thoroughly.

Sample removal and storage

• Once the test is complete carefully remove the sample from the system, wrap in saline soaked paper towel, place in an appropriately named ziplock bag, and store in the freezer in BioRobotics lab.

  • Be sure to note the anatomical orientation of the sample for consistency in repeatability tests.
• The sample naming convention can be found in data management wiki page.

Data storage

Muscle

Target outcome

Test the muscle sample under confined compression to obtain stress-strain data to examine material properties with repeatable results.

Experiment Conditions

Unconfined compression test to obtain force displacement data from the samples.

Measurements

Force-displacement data (unfiltered @ 2.5 kHz unless downsampled) Video data (RAW format, 640x480 @ 10 Hz unless downsampled)

Operating Procedures

Sample preparation

Thickness measurement

• Once the samples are punched out, measure the thickness using the optical thickness measurement system (OTMS).

Width measurement

• For compression samples the diameter is assumed to be 5mm (from the punch dimensions)

Test set up

Unconfined compression test

• Calibrate the load cell before the test.
• Place the sample on a flat compression platform and fix the whole assembly in a saline bath.
• Test is done at room temperature.
• Current sample size 7mm high (9mm radius)

Note: 1. Determine Reference Thickness

Testing

Unconfined Compression test

• Thickness obtained from OTMS is used to calculate required strains and strain measurements.

• To find the initial position to begin testing use 'find contact' protocol.

• Use force filter.

• Preload to 0.3 gf at a loading rate of 0.005 mm/s
• Wait: 1 min.
• Note the position.
• Unload by 1mm

2. Unconfined Compression Test

• Do not use force filter

• Use compression preconditioning protocol.
• Move Absolute: to bring sample to the reference initial position @ 0.005 mm/s
• Move Relative: to load sample (by 7.5% nominal strain)
• Sinusoidal: preconditioning with an amplitude of 7.5% strain for 1000 cycles at 2 Hz.
• Move Relative: to unload sample (by 7.5% nominal strain)
• Unload completely by 1mm.

• Make sure for each step of the test sequences the location of file is appropriately selected.
• All data is stored in data.txt file in a main data folder. After the test is complete move this file to appropriate folder with the right specimen name. For naming convention go to Specifications/DataManagement
• Maintain a readme.txt file in the specimen master specimen folder to note down any relevant information for all the tests performed for the specimen.

Data analysis

• Once the test is complete, the acquired data is reviewed using the Mach1 Analysis software. The test should be repeated if necessary.
• The data can be loaded and visualized in the analysis software, and if the rates and duration for which the rate is applied are as expected, the data will pass the check. Alternatively, the data can be run through the analysis python script to assess the data quality more thoroughly.

Sample removal and storage

• Once the test is complete carefully remove the sample from the system, wrap in saline soaked paper towel, place in an appropriately named ziplock bag, and store in the freezer in BioRobotics lab.

  • Be sure to note the anatomical orientation of the sample for consistency in repeatability tests.
• The sample naming convention can be found in data management wiki page.

Data storage