Design and Testing of a Pulsatile Conditioning System for Dynamic Endothelialization of Polyphenol-Stabilized Tissue Engineered Heart Valves

Abstract

Heart valve tissue engineering requires biocompatible and hemocompatible scaffolds that undergo remodeling and repopulation, but that also withstand harsh mechanical forces immediately following implantation. We hypothesized that reversibly stabilized acellular porcine valves, seeded with endothelial cells and conditioned in pulsatile bioreactors would pave the way for next generations of tissue engineered heart valves (TEHVs). A novel valve conditioning system was first designed, manufactured and tested to adequately assess TEHVs. The bioreactor created proper closing and opening of valves and allowed for multiple mounting methods in sterile conditions. Porcine aortic heart valve roots were decellularized by chemical extractions and treated with penta-galloyl glucose (PGG) for stabilization. Properties of the novel scaffolds were evaluated by testing resistance to collagenase and elastase, biaxial mechanical analysis, and thermal denaturation profiles. Porcine aortic endothelial cells were seeded onto the leaflets and whole aortic roots were mounted within the dynamic pulsatile heart valve bioreactor system under physiologic pulmonary valve pressures and analyzed after 17 days for cell viability, morphology, and metabolic activity. Our tissue preparation methods effectively removed cells, including the potent α-Gal antigen, while leaving a well preserved extra-cellular matrix scaffold with adequate mechanical properties. PGG enhanced stabilization of extracellular matrix components but also showed the ability to be reversible. Engineered valve scaffolds encouraged attachment and survival of endothelial cells for extended periods and showed signs of widespread cell coverage after conditioning. Our novel approach shows promise toward development of sturdy and durable TEHVs capable of remodeling and cellular repopulation.

In Vitro Comparison of Novel Polyurethane Aortic Valves and Homografts After Seeding and Conditioning

“…in cardiovascular tissue engineering, Jockenhoevel et al 34 and other research groups showed that flow-depending mechanical stress induces ECM formation. 35 in line with these results, the establishment of an ECM and the habituation of the cells were observed during the 5-day conditioning periods, demonstrated by positive staining against collagen iV and fibronectin. An increased ECM growth on scaffolds' inner/flow surface proved the flow dependence.…”

Bioreactor conditioning of valve scaffolds seeded internally with adult stem cells

“…During harvesting of the aortic roots, we preserved about 2 cm of aorta above the sinus of Valsalva and 4 to 5 cm of endocardial tissue (thinned to 2–3 mm) and the anterior mitral leaflet. The coronary arteries were ligated using 2.0 TiCron suture and valves were immersion-decellularized with detergents and enzymes and sterilized according to published protocols [17]. To stabilize the valve ECM, the acellular roots were treated with 0.1% PGG, a collagen binding polyphenol [17].…”

Pulmonary heart valve replacement using stabilized acellular xenogeneic scaffolds; effects of seeding with autologous stem cells

“…Valve-derived scaffolds are preferred because of easy accessibility, outstanding hemodynamic properties and the preservation of biological "niches" after decellularization (10)(11)(12). We also treat acellular scaffolds with penta-galloyl glucose (PGG) for tissue stabilization, to prevent premature scaffold degradation and to reduce calcification (13)(14)(15).…”