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Cyclical Isotropic Radial Stretch Causes Aortic Valve Interstitial Cells To Migrate And Align In A 3D Hydrogel
Toni M. West, Miles W. Massidda, Aaron B. Baker, Michael S. Sacks.
University of Texas, Austin, TX, USA.

OBJECTIVE: In heart valves, Valve Interstitial Cells (VICs) are preferentially aligned with the circumferential direction of the valve, which also correlates with the major direction of collagen fibers. On every beat of the heart, heart valves cyclically undergo anisotropic biaxial stretch. In congenital heart valve defects, there is a correlation between the differences in stretch patterns, and the misalignment of collagen fibers and VICs. To determine if VICs align themselves uniquely in reaction to differing cyclical stretch patterns in a 3D environment, we conditioned VIC-impregnated hydrogels with cyclical isotropic radial stretch using geometric wave patterns. Since VICs align preferentially in the circumferential direction in normal valves, which is the direction where more stretch occurs, we hypothesized that VICs would align parallel to the direction of stretch but would not migrate greatly from their original random positions within the gel.
METHODS: VICs isolated from normal porcine aortic valves were introduced into poly (ethylene) glycol (PEG) hydrogels with MMP-degradable crosslinkers, equilibrated to the gel environment for 3 days, and then conditioned for 48 hours with 1 Hz wave forms. Hydrogels were fixed, stained, and imaged to determine their cytoplasmic orientation with respect to the direction of stretch. Static controls were performed simultaneously. Images were analyzed with Matlab and Paraview to determine the angle of incidence between the major axis of each cell and the direction of radial stretch.
RESULTS: In all waveforms tested, the VICs migrated and aligned into an annulus within the PEG gel, with cells in the annulus patterning based on radius length from the center of the sample. In contrast, static controls had cells randomly aligned.
CONCLUSIONS: VICs migrate in response to cyclical isotropic radial stretch conditioning to align according to the stretch applied.


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