Successful endothelial monolayer formation on melt electrowritten scaffolds under dynamic conditions to mimic tunica intima

Abstract

The lack of transplantable tissues and organs as well as the limitations of synthetic implants highlight the need for tissue-engineered constructs to obtain safe, long-lasting, and limitless tissue replacements. Scaffolds for cardiovascular applications, such as for a tissue-engineered vascular graft (TEVG), are thus highly required. For TEVGs, tubular scaffolds should support the formation of confluent endothelial layers in particular under dynamic conditions to prevent thrombosis and maintain hemostasis. For that purpose, a porous and highly diffusible scaffold structure is necessary to allow optimal cell adhesion as well as oxygen and nutrient exchange with the surrounding tissue. Here, we present a three-dimensional-printed scaffold made by a combination of fused deposition modeling (FDM) and melt electrowriting (MEW) out of polycaprolactone that enables monolayer formation and alignment of endothelial cells in the direction of medium flow under a shear stress of up to 10 dyn cm-2. Pore size and coating with human fibrin were optimized to enable confluent endothelial layers on the printed scaffold structures. Cell orientation and shape analysis showed a characteristic alignment and elongation of the tested endothelial cells with the direction of flow after dynamic cultivation. In contrast, melt electrospun scaffolds based on the same CAD design under comparable printing and cultivation conditions were not sufficient to form gapless cell layers. Thus, the new scaffold fabricated by MEW/FDM approach appears most suitable for TEVGs as a template for the innermost vascular wall layer, the tunica intima.