3D Bioprinting-Tunable Small-Diameter Blood Vessels with Biomimetic Biphasic Cell Layers

Blood vessel damage resulting from trauma or diseases presents a serious risk of morbidity and mortality. Although synthetic vascular grafts have been successfully commercialized for clinical use, they are currently only readily available for large-diameter vessels (>6 mm). Small-diameter vessel (<6 mm) replacements, however, still present significant clinical challenges worldwide. The primary objective of this study is to create novel, tunable, small-diameter blood vessels with biomimetic two distinct cell layers [vascular endothelial cell (VEC) and vascular smooth muscle cell (VSMC)] using an advanced coaxial 3D-bioplotter platform. Specifically, the VSMCs were laden in the vessel wall and VECs grew in the lumen to mimic the natural composition of the blood vessel. First, a novel bioink consisting of VSMCs laden in gelatin methacryloyl (GelMA)/ polyethylene(glycol)diacrylate/alginate and lyase was designed. This specific design is favorable for nutrient exchange in an ambient environment and simultaneously improves laden cell proliferation in the matrix pore without the space restriction inherent with substance encapsulation. In the vessel wall, the laden VSMCs steadily grew as the alginate was gradually degraded by lyase leaving more space for cell proliferation in matrices. Through computational fluid dynamics simulation, the vessel demonstrated significantly perfusable and mechanical properties under various flow velocities, flow viscosities, and temperature conditions. Moreover, both VSMCs in the scaffold matrix and VECs in the lumen steadily proliferated over time creating a significant two-cell-layered structure. Cell proliferation was confirmed visually through staining the markers of alphasmooth muscle actin and cluster of differentiation 31, commonly tied to angiogenesis phenomena, in the vessel matrices and lumen, respectively. Furthermore, the results were confirmed quantitatively through gene analysis which suggested good angiogenesis expression in the blood vessels. This study demonstrated that the printed blood vessels with two distinct cell layers of VECs and VSMCs could be potential candidates for clinical small-diameter blood vessel replacement applications.