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Passive stress-strain measurements in the stage-16 and stage-18 embryonic chick heart
C E Miller1, M A Vanni, L A Taber
1Department of Mechanical Engineering, University of Rochester School of Medicine and Dentistry, NY 14642, USA.
Insights
This study presents the first stress-strain measurements of embryonic heart tissue, revealing nonlinear mechanical properties and significant hysteresis. These findings provide crucial data for understanding early cardiovascular development and tissue mechanics.
Area of Science:
- Biomedical Engineering
- Developmental Biology
- Cardiovascular Physiology
Background:
- Characterizing the mechanical properties of embryonic cardiovascular tissue is essential for understanding heart development and morphogenesis.
- Previous studies have lacked detailed biomechanical data on the mechanical behavior of the primitive embryonic ventricle.
Purpose of the Study:
- To perform the first stress-strain measurements on embryonic cardiovascular tissue using cyclic uniaxial loading of the primitive ventricle.
- To characterize the material properties of embryonic chick ventricles at Hamburger/Hamilton stages 16 and 18.
- To develop a finite element model to describe the pseudoelastic behavior of stage-18 embryonic myocardium.
Main Methods:
- Excised ventricular segments from Hamburger/Hamilton stage-16 or -18 chick embryos were subjected to cyclic uniaxial loading.
- A real-time video tracking system measured myocardial surface strains, while a force transducer recorded stress.
- Data were used to generate stress-strain curves and a finite element model was fitted to experimental data.
Main Results:
- Stress-strain curves for embryonic cardiovascular tissue were nonlinear, even at low strain levels.
- Significant hysteresis was observed, with mean hysteresis energy accounting for 36% (stage 16) and 41% (stage 18) of total stored strain energy.
- The fitted exponential parameter for the pseudoelastic strain-energy function was lower than in mature myocardium, suggesting lower fiber content in immature tissue.
Conclusions:
- This study provides the first quantitative biomechanical characterization of embryonic cardiovascular tissue.
- The observed nonlinear stress-strain behavior and hysteresis are key features of immature myocardial mechanics.
- These findings establish a baseline for future studies on cardiac development, disease, and tissue engineering, aiming to identify biomechanical factors regulating growth and morphogenesis.
Abstract:
The first stress-strain measurements on embryonic cardiovascular tissue are described here, obtained from cyclic uniaxial loading of the primitive ventricle. An excised ventricular segment from Hamburger/Hamilton stage-16 or stage-18 chicks (2-1/2 and 3 days of a 21-day incubation period) was mounted longitudinally between two small wires in oxygenated Krebs-Henseleit cardioplegia solution. One wire was attached to an ultrasensitive force transducer and the other to a Huxley micromanipulator controlled by remote motor drive. A real-time video tracking system calculated three myocardial surface strains based on the positions of three surface markers while the heart was deformed in a triangular wave pattern. Force transducer output was filtered, digitally sampled, and stored with strains and time. Results were plotted as strain (longitudinal, circumferential, shear, and principal) versus time, stress versus time, and stress versus longitudinal strain. The stress-strain curves were nonlinear, even at low strain levels. The hysteresis loops were large; mean hysteresis energy as a proportion of total cycle stored strain energy was 36 percent (stage 16) and 41 percent (stage 18). We created a finite element model of the ventricle and fit the model behavior to the experimental behavior to determine parameters for a stage-18 pseudoelastic strain-energy function of exponential form. The calculated exponential parameter is significantly lower than that found in corresponding uniaxial studies of mature myocardium, possibly indicating the lower fiber content of the immature tissue. The results of this study are the first step in characterizing material properties for comparisons with later developmental stages and with impaired and altered myocardium. The long-term goal is to aid in identifying the biomechanical factors regulating growth and morphogenesis.