• Specifications
• ExperimentationTissueMechanics
• ProtocolEvaluation

TableOfContents

Synopsis

• All the attempts to evaluate the tissue mechanical testing and related protocols will be documented on this page.

• Note: The force data will not be filtered.

• Force displacement data will be acquired at 100 Hz.

• Load cell will be calibrated at the beginning of the test day. -- ["colbrunn"] DateTime(2015-08-25T15:31:29Z) Is the load cell actually being calibrated, or is this just a confirmation of the calibration? What is the procedure for the "calibration"?

• Appropriate changes will be made to ["Specifications/ExperimentationTissueMechanics"] once evaluation of protocols is complete.
• Details of testing protocols can be found at ["Specifications/ExperimentationTissueMechanics"]

  -- ["colbrunn"] DateTime(2015-08-25T15:59:47Z) there are some typos in the strain amounts. verify that the values for repeatability are the same within a test. e.g. some are 5, 10, 15% and then it is repeated as 3, 6, 9%.

• Note: After the repeatability test of each tissue type, the sample will be stored in the refrigerator and will be tested for reproducibility, to avoid effects of multiple freeze-thaw cycles.

Repeatability of test protocols

• -- ["colbrunn"] DateTime(2015-08-25T15:47:36Z) It is not clear why the percent strain is changing from one repeatability test to the other. Is this right? If so, can this be explained "why" in this section?

• This exercise will be used to evaluate whether the Mach 1 system can apply the same controls when the test environment is not changed. This will also help to determine whether there was any tissue damage/ altered tissue state during the test (if the controls remain the same).
• Ligament tensile test
  • A ligament tensile sample will be tested at 3%, 6% and 9% strain at 20%/s strain rate.
  • After the completion of first test, the sample will be allowed to rest in an unloaded state for 30 min.
  • The sample will not be removed from the test environment.
  • The sample will be tested again at 3%, 6% and 9% strain at 20%/s strain rate.
  • The sample will be allowed to rest in an unloaded state for 30 min.
  • The sample will be tested at 3%, 6% and 9% strain at 100%/s strain rate.
  • The sample will be allowed to rest again in an unloaded state for 30 min.
  • The sample will be tested again at 3%, 6% and 9% strain at 100%/s strain rate.
• Cartilage unconfined compression test
  • A cylindrical cartilage sample will be tested under unconfined compression at 5%, 10% and 15% strain at 20%/s strain rate.
  • After completion of the test, the sample will be allowed to rest in an unloaded state for 30 min.
  • The sample will not be removed from the test environment.
  • The sample will be tested again at 5%, 10% and 15% strain at 20%/s strain rate.
  • The sample will be allowed to rest in an unloaded state for 30 min.
  • The sample will be tested at 5%, 10% and 15% strain at 100%/s strain rate.
  • The sample will be allowed to rest again in an unloaded state for 30 min.
  • The sample will be tested again at 5%, 10% and 15% strain at 100%/s strain rate.
• Cartilage confined compression test
  • Sample used for unconfined compression will now be tested under confined compression.
  • All steps described above for unconfined compression test will be repeated.
• Cartilage tensile test
  • A cartilage tensile sample will be tested at 5%, 10% and 15% strain at 20%/s strain rate.
  • After completion of the test, the sample will be allowed to rest in an unloaded state for 30 min.
  • The sample will not be removed from the test environment.
  • The sample will be tested again at 5%, 10% and 15% strain at 20%/s strain rate.
  • The sample will be allowed to rest in an unloaded state for 30 min.
  • The sample will be tested at 5%, 10% and 15% strain at 100%/s strain rate.
  • The sample will be allowed to rest again in an unloaded state for 30 min.
  • The sample will be tested again at 5%, 10% and 15% strain at 100%/s strain rate.
• Meniscus unconfined compression test
  • A cylindrical meniscus sample will be tested under unconfined compression at 5%, 10% and 15% strain at 20%/s strain rate.
  • After completion of the test, the sample will be allowed to rest in an unloaded state for 30 min.
  • The sample will not be removed from the test environment.
  • The sample will be tested again at 5%, 10% and 15% strain at 20%/s strain rate.
  • The sample will be allowed to rest in an unloaded state for 30 min.
  • The sample will be tested at 5%, 10% and 15% strain at 100%/s strain rate.
  • The sample will be allowed to rest again in an unloaded state for 30 min.
  • The sample will be tested again at 5%, 10% and 15% strain at 100%/s strain rate.
• Meniscus confined compression test
  • Sample used for unconfined compression will now be tested under confined compression.
  • All steps described above for unconfined compression test will be repeated.
• Meniscus tensile test
  • A meniscus tensile sample will be tested at 5%, 10% and 15% strain at 20%/s strain rate.
  • After completion of the test, the sample will be allowed to rest in an unloaded state for 30 min.
  • The sample will not be removed from the test environment.
  • The sample will be tested again at 5%, 10% and 15% strain at 20%/s strain rate.
  • The sample will be allowed to rest in an unloaded state for 30 min.
  • The sample will be tested at 5%, 10% and 15% strain at 100%/s strain rate.
  • The sample will be allowed to rest again in an unloaded state for 30 min.
  • The sample will be tested again at 5%, 10% and 15% strain at 100%/s strain rate.

Results

• Parameters to be evaluated: Root mean square error between forces as well as displacements (peak and relaxed) between tests conducted at a given strain rate (done for both 20%/s and 100%/s strain rates).
• This comparison will be done for all tissue and test types.

=== Reproducibility of test protocols === -- ["colbrunn"] DateTime(2015-08-25T15:47:36Z) Reproducibility is typically considered to be comparison between different operators or on different equipment. In this case, you are still looking at repeatability, just across multiple days. Right? Is this what you want? If so, you might want to add a few sentences here to clarify what you mean by Reproducibility.

• The goal of this exercise is to evaluate whether repeating the test protocols will produce the same results (evaluated through material property identification) provided the sample was not damaged during testing.

• The samples tested in previous section will be removed from the test set up and stored before being retested. -- ["colbrunn"] DateTime(2015-08-25T15:47:36Z) Stored in what conditions? For how long?

• Sample dimensions will be measured again before testing.

• Ligament tensile test
  • A ligament tensile sample will be tested at 3%, 6% and 9% strain at 20%/s strain rate.
  • After the completion of first test, the sample will be allowed to rest in an unloaded state for 30 min.
  • The sample will not be removed from the test environment.
  • The sample will be tested again at 3%, 6% and 9% strain at 100%/s strain rate.
• Cartilage unconfined compression test
  • A cylindrical cartilage sample will be tested under unconfined compression at 5%, 10% and 15% strain at 20%/s strain rate.
  • After completion of the test, the sample will be allowed to rest in an unloaded state for 30 min.
  • The sample will not be removed from the test environment.
  • The sample will be tested again at 5%, 10% and 15% strain at 100%/s strain rate.
• Cartilage confined compression test
  • Sample used for unconfined compression will now be tested under confined compression.
  • All steps described above for unconfined compression test will be repeated.
• Cartilage tensile test
  • A cartilage tensile sample will be tested at 5%, 10% and 15% strain at 20%/s strain rate.
  • After completion of the test, the sample will be allowed to rest in an unloaded state for 30 min.
  • The sample will not be removed from the test environment.
  • The sample will be tested again at 5%, 10% and 15% strain at 100%/s strain rate.
• Meniscus unconfined compression test
  • A cylindrical meniscus sample will be tested under unconfined compression at 5%, 10% and 15% strain at 20%/s strain rate.
  • After completion of the test, the sample will be allowed to rest in an unloaded state for 30 min.
  • The sample will not be removed from the test environment.
  • The sample will be tested again at 5%, 10% and 15% strain at 100%/s strain rate.
• Meniscus confined compression test
  • Sample used for unconfined compression will now be tested under confined compression.
  • All steps described above for unconfined compression test will be repeated.
• Meniscus tensile test
  • A meniscus tensile sample will be tested at 5%, 10% and 15% strain at 20%/s strain rate.
  • After completion of the test, the sample will be allowed to rest in an unloaded state for 30 min.
  • The sample will not be removed from the test environment.
  • The sample will be tested again at 5%, 10% and 15% strain at 100%/s strain rate.

Results

• Parameters to be evaluated: Root mean square error between stresses as well as strains (peak and relaxed) between tests conducted at a given strain rate (done for both 20%/s and 100%/s strain rates).
  • This comparison will be done for all tissue and test types.

Assessment of desired rates and strain levels

• The data acquired with all the previous tests will be evaluated to make sure the applied rates and strain levels match the desired rates and strain levels.
• Note: A python script is being developed to analyze the data quality as soon as the data is acquired (parameters of interest will be applied rates ans strain levels, expected time taken vs desired time taken, instantaneous and relaxed moduli calculation as well as plotting data to visually inspect data quality).

Results

• Parameters to be evaluated: Difference between desired and applied rates and strain level (% error).

Assessment of force and displacement data alignment

• Provided the acquired data is not filtered the displacement and force data should align in time.
• The data acquired with the repeatability and reproducibility tests will be evaluated to make sure the displacements and forces are aligned.

Results

• Records of time stamps at the beginning and end of force and displacement.

Zero force (find contact) with and without force filter

• It is recommended to not use any force data filtering during testing data acquisition. However, to find zero force (10gf) for initial length measurement, it may be difficult to measure 10gf without filtering.
• For each type of tissue sample ( ligament tensile sample, cartilage compression sample, cartilage tensile sample, meniscus compression sample and meniscus tensile sample), 10 readings will be taken for zero force measurement with and without force filter to assess the feasibility of not using a force filter.
• A very slow rate (0.01mm/s) will be used.

Results

• Displacement at which the 10gf is reached will be compared.

Assessment of positioning of clamps to set zero position

• As the zero position of the clamps for tensile tests is set manually through visual inspection, it may be under or overestimated.
• To assess effects of experimenter error, two users will test the systems one after the other. First user will record the position/ displacement at the beginning and will later move the clamps to estimate zero position. Without removing the clamps from the set up, another user will move the clamps away from each other (vertically) and at a given distance record the value of position. He/she will then move the clamps to estimate the zero position . The distance moved by the two users will then be compared to assess user error.

Results

• A visual estimate of zero position of user two will be compared to value showing on the screen from previous user's estimate of zero position.

Length measurement repeatability and reproducibility

• For this test a ligament tensile sample, a meniscus tensile sample and a cartilage tensile sample will be used.
• To test repeatability of the procedure, the samples lengths will be measured 5 times
  • without removing the sample from the test set up.
• The samples will be taken out of the measuring set up and put back in after a few hours and all the measurements will be repeated again to check for reproducibility of results (set ups will be re-calibrated before the reproducibility tests, i.e. zero position).

Results

• Root mean square error

Thickness measurement repeatability and reproducibility

• For this test a ligament tensile sample, cartilage compression sample,a cartilage tensile sample, a meniscus compression sample and a meniscus tensile sample will be used.
• To test repeatability of the procedure, the samples thicknesses will be measured 5 times (each time 5 measurements are taken on the sample and averaged) without moving the sample.
• The thickness will be measured both optically and with the lvdt system.
• The samples will be taken out of the measuring set ups and put back in after a few hours and all the measurements will be repeated again to check for reproducibility of results (set ups will be re-calibrated before the reproducibility tests).

Results

• Average thickness values and standard deviations will be reported.

Standardization of camera positions using bigger lens

• A simple set up will be built for optical tissue thickness measurement (OTTM).
• A base with a fixed platform fitted with a standard precision gage will be built.
• A blue background will be attached to the far edge of the base.
• Distance needed for an optimal image for any tissue placed on the platform will be estimated using the current camera and Mach 1 base.
• This distance will be used to attach a camera to the base of OTTM system. the field of view should cover the sample entirely as well as the height of the gage.

Timeline

Note: The events are organized based on their dependability on results from previous events. Some time might be needed between events to evaluate collected results to decide the progression of following events.

• Day 1 : Data collection for assessment of thickness measurement LVDT and optical.
• Day 2: Assessment of positioning of clamps to set zero position AND standardization of camera positions using bigger lens.
• Day 3: Assessment of zero force (find contact) with and without force filter AND assessment of length measurement repeatability and reproducibility.
• Day 2 and 3: Design optical tissue thickness measurement system.
• Day 4: Repeatability and reproducibility data collection for ligament tensile test.
• Day 5: Repeatability and reproducibility data collection for cartilage unconfined compression test.
• Day 6: Repeatability and reproducibility data collection for cartilage confined compression test.
• Day 7: Repeatability and reproducibility data collection for cartilage tensile test.
• Day 8: Repeatability and reproducibility data collection for meniscus unconfined compression test.
• Day 9: Repeatability and reproducibility data collection for meniscus confined compression test.
• Day 10: Repeatability and reproducibility data collection for meniscus tensile test.
• Day 1-15 : Python scripting/ data analysis.