Engineering Tissue‐Specific, Multiscale Microvasculature with a Capillary Network for Prevascularized Tissue

Abstract

Although there are various pre‐existing technologies for engineering vasculatures, multiscale modeling of the architecture of human vasculature at a capillary scale remains a challenge. In this study, a novel technology is developed for the production of a functional, multiscale microvasculature comprising of endothelialized channels and tissue‐specific capillary networks. Perfusable, endothelialized channels are bioprinted, after which angiogenic sprouts are grown into user‐designed capillary networks. The induction of branched and liver‐lobule‐like capillary networks confirm that the technology can produce various types of tissue‐specific multiscale microvasculatures. Further, the channels and capillaries are deemed to be functional when evaluated in vitro. An ex vivo assay demonstrates that the microvasculature can induce neovessel ingrowth, integrate with host vessels, and facilitate blood flow. Remarkably, blood flows through the implanted capillary network without any change in its morphology. Finally, the technology is applied to produce a vascularized liver tissue; it significantly improves its hepatic function. It is believed that this new technology will create new possibilities in the development of highly vascularized and functional tissues/organs on a clinically relevant scale.

Vascularization in Bioartificial Parenchymal Tissue: Bioink and Bioprinting Strategies

“…Such motifs are present in natural hydrogel materials such as collagen, gelatin, gelatin methacrylol, fibrin, and hyaluronic acid [ 55 , 58 , 61 ]. In alginate, agarose, and PEG hydrogels, such motifs are missing but can be added to the bioink formulation [ 42 , 62 , 63 ]. In a systematic investigation of the viability of human umbilical vein endothelial cells (HUVECs) in various hydrogels of standardized concentrations, Benning et al demonstrated that fibrin, collagen 1, Matrigel, and gelatin hydrogels maintain the viability of integrated HUVECs and enable the attachment of cells [ 64 ].…”

“…Moreover, several bioinks consisting of different supporting materials specifically adapted to the respective cell compositions can be applied in combination on a bioprinting platform [ 14 , 46 ]. HUVECs have been extensively studied for application in biofabrication [ 14 , 21 , 27 , 33 , 39 , 46 , 47 , 50 , 59 , 63 , 83 , 84 , 85 , 86 , 87 , 88 , 89 ]. Functional vessel endothelium produces nitric oxide, thrombomodulin, and tissue plasminogen activator, all inhibitors of thrombus formation [ 36 , 40 ].…”

“…In addition to ECs, pericytes, smooth muscle cells, and fibroblasts participate in vessel network formation [ 14 , 17 , 36 , 42 , 85 , 86 , 89 , 96 ] ( Table 1 ). Thus, there is study evidence that coculture with endothelial-stabilizing cells enhances vessel network formation, e.g., by growth factor secretion and direct cell–cell interactions [ 33 , 42 , 60 , 63 , 89 , 99 ]. Mesenchymal stem cells, sometimes also referred to as medicinal signaling cells [ 100 ], have been widely used in tissue-engineering strategies with the intention of promoting functional vascularization by VEGF secretion [ 17 , 39 , 42 , 58 , 59 , 101 ].…”

“…Sacrificial inks can be bioprinted to shape a template that serves as ‘negative’. Gelatin [ 14 , 22 , 27 , 39 , 47 , 63 , 83 ], alginate [ 87 , 102 , 103 ], Pluronic ® F127 [ 68 , 85 , 86 , 104 , 105 , 106 , 107 ], agarose [ 108 ], poly(vinyl alcohol) [ 109 ], and carbohydrate mixtures [ 43 , 88 ] can serve as sacrificial inks. In a next step, sacrificial templates are embedded in low-viscosity bioinks containing effector cells, which then can be adequately cured [ 110 ].…”

“…Removal can be accomplished by dissolution with a solvent [ 14 , 47 , 85 , 86 , 103 , 106 , 110 , 111 ], temperature regulation [ 14 , 27 , 46 , 83 , 104 , 105 , 106 , 110 ], or pH regulation [ 58 , 85 ], leaving a microfluidic network of patterned microchannels or even vascular tree-like channels in the construct [ 22 , 47 , 83 , 87 , 110 ]. Perfusion of such a network with ECs and their subsequent partial adherence has the potential to result in coating of the inner wall [ 27 , 47 , 63 , 83 , 87 , 105 , 111 ] ( Figure 3 a). Other studies reported a method in which ECs (8–20 × 10 6 /mL) were directly integrated into the sacrificial gelatin core [ 14 , 27 , 46 ].…”