Role of extracellular matrix in the biomechanical behavior of pancreatic tissue.

Correlating the biomechanical properties of tissue with its function is an emerging area of research with potential impact in diagnostics, therapeutics, and prognostics. A critical stepping-stone in developing structure-function models is creating methods that can correlate the tissue structure with its mechanical behavior. As an initial step in addressing this challenge, we have characterized the mechanical behavior of unprocessed pancreatic tissue using optical fiber polarimetric elastography. To correlate the observed behavior to physiologically relevant structural features, a series of architectures are designed and fabricated using 3D printing. The mechanical response of the 3D printed elastomeric structures is analyzed using compressive testing and modeled using finite element analysis. The biomechanical behavior and buckling point of the 3D printed structures is used to create a calibration curve to understand the measured response of the resected pancreatic tissue. Based on the modeling and biomimetic results, the biomechanical behavior of pancreatic tissue is likely due to the collagen IV network.

Hemodynamics and ventricular function in a zebrafish model of injury and repair.

Myocardial infarction results in scar tissue and irreversible loss of ventricular function. Unlike humans, zebrafish has the capacity to remove scar tissue after injury. To assess ventricular function during repair, we synchronized microelectrocardiogram (µECG) signals with a high-frequency ultrasound pulsed-wave (PW) Doppler to interrogate cardiac hemodynamics. µECG signals allowed for identification of PW Doppler signals for passive (early [E]-wave velocity) and active ventricular filling (atrial [A]-wave velocity) during diastole. The A wave (9.0±1.2 cm·s(-1)) is greater than the E wave (1.1±0.4 cm·s(-1)), resulting in an E/A ratio <1 (0.12±0.05, n=6). In response to cryocauterization to the ventricular epicardium, the E-wave velocity increased, accompanied by a rise in the E/A ratio at 3 days postcryocauterization (dpc) (0.55±0.13, n=6, p<0.001 vs. sham). The E waves normalize toward the baseline, along with a reduction in the E/A ratio at 35 dpc (0.36±0.06, n=6, p<0.001 vs. sham) and 65 dpc (0.2±0.16, n=6, p<0.001 vs. sham). In zebrafish, E/A<1 at baseline is observed, suggesting the distinct two-chamber system in which the pressure gradient across the atrioventricular valve is higher compared with the ventriculobulbar valve. The initial rise and subsequent normalization of E/A ratios support recovery in the ventricular diastolic function.