Weekly Update in lieu of Recurring Meeting of Cleveland Clinic Core Team
Date: January 10, 2017
Provided by: Snehal Chokhandre
Ongoing Action Items:
- Review drafts of data manuscripts for submission.
- Complete studies for tissue testing reproducibility.
- Continue tissue testing of Open Knee(s) specimens.
- Continue segmentation of Open Knee(s) specimens.
- Data manuscripts.
- No progress.
- Tissue testing.
- Snehal started testing oks001 lateral femoral condyle cartilage for confined compression, unconfined compression, and tension.
- It appears that some of the tissue strips may have been mislabeled as there is only one small strip for lateral femoral cartilage in the labeled bag but more tissue was taken from the bone based on the observation made from looking at the frozen femur bone.
- Cartilage testing started with unconfined compression test. As per current protocols, 0-15% strain was used for preconditioning. The sample floated away resulting in unacceptable pre-conditioning data.
- Snehal tried to further uniformly slice the sample but the attempt was not successful. Two more samples from adjacent location to the previous sample were made for further testing.
- The new sample was then tested with pre-conditioning between 5-15% strain twice but the sample still floated away. The sample was allowed to stay unloaded to recover for over an hour between these two attempts. An attempt to further uniformly cut this sample yielded in unsatisfactory sample.Hence, the sample was not used further.
- Decided to start with a fresh sample (made previously and kept in fridge in the meantime) and tested it with 10-15% pre-conditioning. The data was satisfactory and testing progressed with stress relaxation. Confined compression test was also performed on the same sample.
- Some specific observations were noted for compression testing of the cartilage. There appeared to be some buckling toward the beginning of the ramps in confined compression. This may be related to positioning of the indenter over the filter/sample. The sample also appeared to be stiffer in 5-10% strain region when compared to 10-15% strain region. This may point to some structural collapse at higher strains. This may also be attributed to the sample itself as the donor was 71 years old. This situation needs further exploration. Using 10-15 % strain range for pre-conditioning was a deviation from current protocol and will need to be evaluated with repeatability analysis.
- Pre-conditioning data for tensile test was not satisfactory and the sample was frozen until further decision would be made on how to proceed. It should be noted that all cartilage tensile repeatability tests exhibited acceptable pre-conditioning data.
- Overall conclusions and actions include the following.
- Nonuniformity of samples seems to be the biggest contributing factor in the quality of data.
- Going forward any repeatability test should be performed with full expected hold times (30 mins) for added confidence.
- Given that there was a protocol deviation in preconditioining for compression tests, repeatability tests using trial samples will be required to make the deviation a part of permanent protocol.
- At the least, two full tests in one day and a third full test the next day (with measuring thickness again etc.) will further increase the confidence in data and testing procedures.
- New tensile specimen from fresh strips taken from the lateral femoral condyle (never thawed since initial harvesting of tissue) will be made to complete the testing set. This will be done once an agreement reaches over cartilage test repeatability for compression tests even though the compression tests for this set/location are complete. These test may also be further repeated for the same sample. If 10-15% strain for preconditioning is agreed upon going forward, it will also be used for meniscus compression samples.
An indentor with a wider tip (< 5mm) may be useful in confined compression to cover a larger area on the filter's surface for a more uniform deformation of sample and avoid buckling of tissue/tipping of filter.
- The parent tissue strip should be kept in the fridge until all the tests for that set are complete in case new samples are needed. Too many freeze-thaw cycles should be avoided. This practice will be noted in the specifications.
- All the data from unsuccessful and successful attempts is backed up on external hard drives in the tissue testing lab and MIDAS along with a readme.txt for details. Thickness measurement information from the OTMS is also uploaded to MIDAS.
- Python scripts to immediately check data quality for both preconditioning and the entire test are working on the Mach-1 computer.
- No progress.
- None noted.