TableOfContents

Synopsis

• All the attempts to evaluate the tissue mechanical testing and related protocols will be documented on this page. These excersices will help determine the capabilities of the testing system, quality of data and the feasibility of protocols.

• Note: The force data will not be filtered.

• Force displacement data will be acquired at 100 Hz.
• Load cell calibration will be confirmed at the beginning of the test day.
• Appropriate changes will be made to ["Specifications/ExperimentationTissueMechanics"] once evaluation of protocols is complete.
• Details of testing protocols can be found at ["Specifications/ExperimentationTissueMechanics"]

• Note: After the repeatability test of each tissue type, the sample will be stored in the refrigerator if tests are going to be repeated the next day, to avoid effects of multiple freeze-thaw cycles.

• Depending on the tissue type, different force transducers will be used.
• Samples used for repeatability tests are different from samples used to optimize other factors before actual tests.
• Both LVDT and optical thickness measurements will be done for these set of tests.

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Repeatability of test protocols without changing the test environment

• 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.
• 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.
• 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.
• 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.
• 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.

Evaluation metrics

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

Analysis

Conclusion

Repeatability of test protocols by changing test environment

• The goal of this exercise is to evaluate whether repeating the test protocols by removing it from the test set up and repeating all the preparation steps before testing it again 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 either at room temperature if test is going to be repeated the same day or in the refrigerator if the test is repeated the next day.
• 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.
• 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.
• Cartilage confined compression test
  • Sample used for unconfined compression will now be tested under confined compression.
  • 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.
• 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.
• Meniscus confined compression test
  • Sample used for unconfined compression will now be tested under confined compression.
  • 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.

Evaluation metrics

• Parameters to be evaluated: moduli values
• This comparison will be done for all tissue and test types.

Analysis

Conclusion

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).

Evaluation metrics

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

Analysis

Conclusion

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.

Evaluation metrics

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

Analysis

Conclusion

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.

Evaluation metrics

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

Analysis

Conclusion

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 zero the position of the clap randomly and move the clamp till it is aligned with the other clamp and make a note of the distance moved. He/she will move the clamp away from the aligned position. Second user will then align the clamps and note the distance moved. The two distances recorded by the users will be compared to assess user error.

Evaluation metrics

• 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.

Analysis

• attachment:zero-position.ods

Conclusion

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).

Evaluation metrics

• Root mean square error

Analysis

Conclusion

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).

Evaluation metrics

• Average thickness values and standard deviations will be reported.

Analysis

Conclusion

Assessment of uncertainties associated with fluid forces and inertial forces

Evaluation metrics

Analysis

Conclusion

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.
• see details in Specifications/ExperimentationTissueThickness

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.

• Development of measurement and analyses tools.
  • Day 1-10: Design and build optical tissue thickness measurement system.
  • Day 1-10 : Python scripting for data analysis.
• Protocol assessment
  • Day 11: Assessment of positioning of clamps to set zero position AND standardization of camera positions using bigger lens.
  • Day 12: Data collection for assessment of thickness measurement LVDT and optical.
  • Day 13: Assessment of zero force (find contact) with and without force filter AND assessment of length measurement repeatability and reproducibility.
  • Day 14: Repeatability data collection for ligament tensile test.
  • Day 15: Repeatability data collection for cartilage unconfined compression test.
  • Day 16: Repeatability data collection for cartilage confined compression test.
  • Day 17: Repeatability data collection for cartilage tensile test.
  • Day 18: Repeatability data collection for meniscus unconfined compression test.
  • Day 19: Repeatability data collection for meniscus confined compression test.
  • Day 20: Repeatability data collection for meniscus tensile test.

Evaluation tools

• Currently a python script is in development to analyze the tissue testing data immediately after the mechanical test is done. The goal of this script is to check the data quality for any discrepancy so that the test can be repeated if necessary.
• The repeatability analyses will also help to establish confidence in the testing system and protocols.
• Example: Three loading ramps for cartilage unconfined compression test. Data from 'Move Relative' command for three strain levels from the Mach1 system. Figure below shows displacement applied by the system and resultant loads.

ImageLink(FMC-MCXX-01-01.png, width=800, alt=FMC-MCXX-01-01)