Skip to main content
2023 BMES Annual Meeting Main banner
Icon Legend
This session is not in your schedule.
This session is in your schedule. Click again to remove it.
Back

    Cardiovascular Engineering

    (G-266) Investigating the Contribution of the Extracellular Matrix to Porcine Heart Viscoelasticity

    Saturday, October 14, 2023
    9:30 AM – 10:30 AM PDT
    Location: Exhibit Hall - Row G - Poster # 266

      Presenting Author(s)

    • KK

      Kyle Y. Kunisaki (he/him/his)

      Undergraduate Student
      University of California Santa Barbara
      Eagan, Minnesota, United States

      • Co-Author(s)

    • MG

      Marissa Gionet-Gonzales, PhD

      Postdoctoral Researcher
      University of California, Santa Barbara, United States

    • JR

      Jonah M. Rosas

      PhD Candidate
      University of California, Santa Barbara, United States

    • AP

      Angela A. Pitenis

      Assistant Professor
      University of California, Santa Barbara, United States

    • BP

      Beth Pruitt

      Professor
      University of California, Santa Barbara, United States

      • Primary Investigator(s)

    • RS

      Ryan Stowers

      Assistant Professor
      University of California, Santa Barbara, United States

    Introduction:: Heart disease causes 1 out of every 5 deaths in the United States, and is the leading cause of death worldwide. Prior mechanobiology studies have shown that during disease progression the mechanical properties of heart tissue change, such as an increase in stiffness of the left ventricular wall in cardiomyopathy. However, viscoelasticity, which describes the solid-like elastic response and liquid-like viscous dissipation, has been understudied and typically indirectly through modalities such as ultrasound. Furthermore, viscoelasticity is an important biological property that influences several cell functions such as proliferation and differentiation. We hypothesize that extracellular matrix (ECM) remodeling is a large contributor to disease-associated changes in cardiac viscoelasticity. We measured viscoelasticity of cardiac tissue directly by performing stress relaxation tests using a rheometer and a microindenter. We then characterized the mechanical properties of porcine cardiac ECM via decellularization and mechanical testing.

    Materials and Methods:: 2-3 mm thick, and 15mm long sections were excised from the left ventricle of porcine cardiac tissue. The sections were placed in 1% SDS at 60 rpm and 4℃ to decellularize the tissue. After this treatment the tissues were washed in 1X DPBS for 30 minutes to wash away remaining SDS. Three conditions were used: no decellularization (full cells), two day decellularization (some cells), and four day decellularization (no cells) (Figure 1A). All three conditions were tested on a microindenter at 10% strain to find stress relaxation times. Following this step, the tissue was embedded in Tissue-Tek O.T.C. and sectioned into 40µm thick sections using a cryostat. These sections were stained with picrosirius red and DAPI. Picrosirius red was used to stain the collagen fibers, which was analyzed by CT-FIRE. Using CT-FIRE collagen width, length, and straightness could be found and confirm whether the ECM was intact after decellularization. DAPI was used to stain nuclei of cells and analyzed using Image J’s particle analyzer function to count the number of cells present and confirm cellular removal.

    Results, Conclusions, and Discussions::

    Results


    From histology we confirmed cellular removal and preservation of overall ECM structure. DAPI stains reveal that the decellularization protocol removed most of the cells in the two day condition and completely removed cells in the four day condition (Figure 1B). From the stress relaxation tests we found the mean relaxation time for the two day and the four day conditions to be about 20 seconds (Figure 1C). While slower relaxing than native cardiac tissue (10 seconds) this is still much faster than skeletal muscle tissue. Lastly, the picrosirius red stains, coupled with CT-FIRE analysis, reveal that collagen straightness (Figure 1D) and length do not significantly change. However, the width of collagen fibers (Figure 1E) seemed to slightly decrease across the two day decellularized and four day decellularized conditions.


     


    Discussion


    The results confirm that during decellularization cells are removed and that the overall ECM structure does not significantly change. However, it seems that this process decreases the width of collagen fibers in the ECM, suggesting that the collagen may become less densely packed. Despite this change, the mean stress relaxation times for the two day decellularized and four day decellularized conditions are not significantly different, and it is still very fast relaxing. This suggests that the ECM is indeed a large contributor to the fast relaxing property of cardiac muscle tissue. 


     


    Conclusion


    This study demonstrates that the ECM contributes to the fast relaxing property of cardiac tissue. These results are important to further our understanding of the unique stress relaxation properties of cardiac tissue. For future work, a gentler decellularization process will be explored to preserve collagen architecture to more accurately measure ECM stress relaxation. We also will stain for GAG and Elastin which are ECM proteins known to contribute to viscoelasticity. Overall, this work will allow us to create more accurate cardiac models and further understand the role of viscoelasticity in heart function.



    Acknowledgements (Optional): :

    References (Optional): :