Description
Although Left Ventricle Assist Device (LVAD) support has enhanced the quality of life for many heart failure patients, its prolonged in-vivo implantation causes change in hemodynamics and biomechanics of the aortic heart valve eventually leading to development of aortic insufficiency (AI). The LVAD decreases pressure in the left ventricle, leading to high transvalvular pressure and reduced aortic valve opening. Our hypothesis is that the increased pressure leads to increased mechanical stretch in the aortic valve leaflets, inducing a cascade of responses that ultimately result in local tissue fibrosis and AI. The goal of this study is to investigate the mechanism behind this hypothesis using the methods of tissue engineering. A bioreactor has been built that imparts cyclic stretch and flow to small 3-D constructs of living cells cultured in a silicone membrane. The approach is to use this device for in vitro tissue culture of vascular interstitial cells (VICs) embedded in a collagen gel, which will be subjected to normal and altered stretch and shear representative of the in vivo valve biomechanics. The bioreactor was validated to measure the amount of stretch and shear it can impart to closely replicate in-vivo conditions using PIV technique and ImageJ software. Mean longitudinal strain of 0.037cm (SD= ±0.013cm) was recorded with mean perpendicular strain being 0.0046cm (SD= ±0.0169cm). Measured average shear stress imparted at 100ml/min was 2.735 dynes/cm2 (SD= ±2.25 dynes/cm2) with 6.21 dynes/cm2 (SD= ±3.35 dynes/cm2) at 200ml/min. The cells that underwent cycles of stretch and shear in the bioreactor were screened for formation of myofibroblast using techniques of immunohistochemistry. The marker used was _ smooth muscle actin (SMA) which identifies pathological differentiation of the CPCs to myofibroblast. Yhe expression of the myofibroblast phenotype is a feature of valvupathy. In case of Shear Vs Static control, the mean value for SMA expression for shear was 3.13±1.4 units while for static it was 10.9±7.7 units. In the case of Stretch Vs Static control, the stretched cells showed a mean expression of 8.5±3.95 units while its control counterparts depicted a mean expression of 5.35± 3.69 units.
