Rapid and efficient in vivo angiogenesis directed by electro-assisted bioprinting of alginate/collagen microspheres with human umbilical vein endothelial cell coating layer

Rapid reconstruction of functional microvasculature is the urgent challenge of regenerative medicine and ischemia therapy development. The purpose of this study was to provide an alternative solution for obtaining functional blood vessel networks in vivo, through assessing whether hydrogel-based microspheres coated by human umbilical vein endothelial cells (HUVECs) can direct rapid and efficient in vivo angiogenesis without the addition of exogenous growth factors or other supporting cells. Uniform alginate microspheres with adjustable diameter were biofabricated by electro-assisted bioprinting technology. Collagen fibrils were evenly coated on the surface of alginate microspheres through simple self-assembly procedure, and collagen concentration is optimized to achieve the highest HUVECs adhesion and proliferation. Immunofluorescence staining and gene analysis confirmed the formation of the prevascularized tubular structure and significantly enhanced endothelial gene expression. HUVECs-coated hydrogel microspheres with different diameters were subcutaneously injected in immunedeficient mice, which demonstrated rapid blood vessel regeneration and functional anastomosis with host blood vessels within 1 week. Besides, microsphere diameter demonstrated influence on blood vessel density with statistical differences but showed no obvious influence on the area occupied by blood vessels. This study provided a powerful tool for rapid and minimalinvasion angiogenesis of bioprinting constructs and a potential method for vascularized tissue regeneration and ischemia treatment with clinically relevant dimensions.