Optimizing biomechanical testing of tissues by enhanced biaxial experimental capabilities

Abstract

Accurate characterization of cardiac tissue material properties is vital for advancing engineering practices, particularly in medical device research. The collective of these studies aims to address gaps in knowledge regarding critical tissue effects through experimental testing and database development. Key objectives include understanding pathological changes in diseased human tissue, defining a transfer function between fresh and formalin-fixed tissues, evaluating tissue changes due to ablation, and enhancing testing systems to support future investigations.Tissue properties were analyzed using biaxial and uniaxial mechanical testing systems. A biaxial TA ElectroForce TestBench and a uniaxial Instron 5943 with a Biopuls submersible bath were used to measure the stress-strain relationships under a variety of physiological conditions. In addition, Green's strain was tracked with overhead cameras to address modeling needs through different biaxial tests. Investigations included cardiac valve material and collagen fiber orientation, experimental development of formalin fixation and refrigeration transfer functions, and evaluation of tissue changes due to ablation. Testing methods were also improved for a variety of tests that include changes to test smaller tissue samples, like leaflets of valves, for future studies. The equibiaxial work produced cyclically tested data that supports the creation of transfer functions and provides data for model verification. Results from one of such studies demonstrated material property variations along the length of the descending aorta, providing insights into physiological stretch effects that aid in validating model predictions. Additionally, Green strain and stress data from esophageal tissues were applied to the Fung model to characterize the material property changes cryoablation has. Progress was also made in developing methodologies to set the foundation for additional databases of tissue properties.