Design of a Novel Ex Vivo Bioreactor to Investigate the Effect of Pressure Induced Stretch on Aortic Valve Biology

Abstract

AbstractA variety of ex vivo bioreactors have been developed to study the mechanobiology of valves and valve substitutes. Especially, bioreactors to mimic the individual mechanical stimuli (stretch, pressure and shear), have been well established. Going forward, it is essential to characterize the structural and biological changes in the aortic valve when subjected to a combination of these stimuli. Especially, since it is expected that a synchronized exposure to combined mechanical stimuli has a significantly different effect than the effect caused by individual stimulus. To this end, a novel bioreactor was designed, fabricated and validated to study the effect of stretch induced by the physiological transvalvular pressure gradient on fresh porcine aortic valve. The ex vivo bioreactor developed in the current study can maintain consistent physiological loading conditions with independent control of the flow rate, pressure and frequency to reproduce clinically relevant mechanical conditions. The design consists of a linear actuator system driving the culture media through the valve at a prescribed flow rate. The pressure levels on either side of the valve can be controlled by using a compliance chamber on the aortic side which is connected to a compressed air circuit. The linear drive system has a piston arrangement at its end, and drives the media in a rigid cylindrical ventricle section. The media returns to the ventricular side though a compliant channel during the reverse motion of the linear actuator. The entire setup is placed inside an incubator maintained at 370 C and 5% CO2. The flow and pressure variations were observed to be physiologically accurate and consistent over the time period of the experiment. Other salient features include low volume of the entire setup, and replaceable valve mounting mechanism to accommodate different sized valves. To ensure that the valve cells are healthy and native phenotype is maintained in the bioreactor, porcine aortic valves were mounted to the stents and subjected to normal physiological conditions of 80/120mmHg pressure, 5 LPM flow rate of Dulbecco’s modified eagle media(DMEM). The entire setup was placed inside an incubator. After 48 hours of culture, Movat Pentachrome stain was done to observe the tissue morphology, and DAPI stain was done to assess the cell viability. Fresh porcine AV leaflets were used as controls. The results were comparable to fresh controls, and indicated that the bioreactor is capable of preserving leaflet morphology and cell viability when cultured under normal physiological conditions for 48 hours.