Rapid casting of patterned vascular networks for perfusable engineered three-dimensional tissues

In the absence of perfusable vascular networks, threedimensional (3D) engineered tissues densely populated with cells quickly develop a necrotic core1. Yet the lack of a general approach to rapidly construct such networks remains a major challenge for 3D tissue culture2–4. Here, we printed rigid 3D filament networks of carbohydrate glass, and used them as a cytocompatible sacrificial template in engineered tissues containing living cells to generate cylindrical networks that could be lined with endothelial cells and perfused with blood under high-pressure pulsatile flow. Because this simple vascular casting approach allows independent control of network geometry, endothelialization and extravascular tissue, it is compatible with a wide variety of cell types, synthetic and natural extracellular matrices, and crosslinking strategies. We also demonstrated that the perfused vascular channels sustained the metabolic function of primary rat hepatocytes in engineered tissue constructs that otherwise exhibited suppressed function in their core. Living tissues have complex mass transport requirements that are principally met by blood flow through multiscale vascular networks of the cardiovascular system. Such vessels deliver nutrients and oxygen to, and remove metabolic byproducts from, all of the organ systems in the body and were critical to the rise of large-scale multicellular organisms5. Although tremendous progress has been made in the past few decades to isolate and culture cells from native tissues, simple methods to generate tissue constructs populated at physiologic cell densities that are sustained by even themost basic vascular architectures have remained elusive. To create perfusable channels in engineered tissues, layer-bylayer assembly6–9 has been explored. In this approach, a trench is moulded into one layer such that a second, separately fabricated layer can then be aligned and laminated to close the lid to form channels in an iterative fashion. However, layer-by-layer assembly is slow and results in seams or other structural artefacts throughout the construct while simultaneously placing considerable design constraints on the materials, channels, and cells used during fabrication. Bioprinting10, in which cells and matrix are deposited dropwise, has been developed over the past decade but also is a slow, serial process with limitations on print resolution, materials, and cells. In contrast to these methods, 3D sacrificial moulding11–13 provides an intriguing alternative. Proof-of-concept studies have shown that a network of channels can be fabricated by creating a rigid 3D lattice of filaments, casting the lattice into