Three-dimensional bioprinting of thick vascularized tissues

Abstract

The advancement of tissue and, ultimately, organ engineering requires the ability to pattern human tissues composed of cells, extracellular matrix, and vasculature with controlled microenvironments that can be sustained over prolonged time periods. To date, bioprinting methods have yielded thin tissues that only survive for short durations. To improve their physiological relevance, we report a method for bioprinting 3D cell-laden, vascularized tissues that exceed 1 cm in thickness and can be perfused on chip for long time periods (>6 wk). Specifically, we integrate parenchyma, stroma, and endothelium into a single thick tissue by coprinting multiple inks composed of human mesenchymal stem cells (hMSCs) and human neonatal dermal fibroblasts (hNDFs) within a customized extracellular matrix alongside embedded vasculature, which is subsequently lined with human umbilical vein endothelial cells (HUVECs). These thick vascularized tissues are actively perfused with growth factors to differentiate hMSCs toward an osteogenic lineage in situ. This longitudinal study of emergent biological phenomena in complex microenvironments represents a foundational step in human tissue generation.

Progress in scaffold‐free bioprinting for cardiovascular medicine

“…As opposed to the surface which can be highly anatomically realistic, when examining the internal cellular architecture of most 3D constructs bioprinted so far,16, 17 their spatial organization is quite simplistic, following easily accessible geometric patterns rather than tissue structure, as tissues incorporate a larger amount of randomness and/or more structural refinement, such as fractal spatial distributions. 3D printing itself could be made ‐ in theory at least, given its high resolution ‐ more naturalistic; thus, this limitation might be considered to originate at the structural design stage.…”

Advances in bioprinted cell-laden hydrogels for skin tissue engineering

“…Contrary to bioassembly, where the minimum fabrication units are pre-formed cell building blocks, bioprinting makes use of fabrication units down to molecular level [78]. Bioprinting processes are capable of printing living and non-living materials in a computercontrolled and automated manner with high levels of resolution, accuracy and reproducibility, enabling the generation of biological substitutes with intricate architectures, precise geometrical configurations and biomechanical heterogeneity [16,80,91,92]. Bioprinting technologies can be classified in three main categories: inkjet bioprinting, laser-assisted bioprinting and extrusion bioprinting (Table 1) [111,125,191].…”

“…In this versatile technology, cell-laden polymeric solutions [28,154], decellularized ECM components [73], cell suspensions [68], microcarriers [162] or tissue spheroids [185] are loaded into standard disposable syringes, and printed onto a building platform driven by pneumatic (pressurized air), mechanical (piston or screw) or solenoid (electrical pulses)-based dispensing systems [76,111,125,137]. An important advantage of extrusion bioprinting is the ability to print highly viscous polymer solutions containing a wide range of cell densities (up 10 7 cells mL -1 ) [92,182]. It also enables the biofabrication of clinically relevant 3D constructs by the deposition of continuous and larger hydrogel strands through a nozzle with variable diameters, usually in a range of 150-300 lm [92,111,125].…”

“…An important advantage of extrusion bioprinting is the ability to print highly viscous polymer solutions containing a wide range of cell densities (up 10 7 cells mL -1 ) [92,182]. It also enables the biofabrication of clinically relevant 3D constructs by the deposition of continuous and larger hydrogel strands through a nozzle with variable diameters, usually in a range of 150-300 lm [92,111,125]. The extrusion bioprinting apparatus typically includes a computer-controlled robotic stage, multiple dispensing systems, and a construction platform that collects the printed material.…”

Technology: The promise of printing

“…A team at Harvard University in Cambridge, Massachusetts, has taken the first steps to overcome that hurdle, printing thick tissue with a rudimentary vascular system and keeping it alive for weeks 5 . The team used three different inks: silicone to give a basic shape; a bioink infused with pluripotent stem cells that would turn into the tissue; and Pluronic, which is a gel at room temperature, but a liquid when cooled.…”