3D Bioprinting for Vascularized Tissue Fabrication

Abstract

3D bioprinting holds remarkable promise for rapid fabrication of 3D tissue engineering constructs. Given its scalability, reproducibility, and precise multi-dimensional control that traditional fabrication methods do not provide, 3D bioprinting provides a powerful means to address one of the major challenges in tissue engineering: vascularization. Moderate success of current tissue engineering strategies have been attributed to the current inability to fabricate thick tissue engineering constructs that contain endogenous, engineered vasculature or nutrient channels that can integrate with the host tissue. Successful fabrication of a vascularized tissue construct requires synergy between high throughput, high-resolution bioprinting of larger perfusable channels and instructive bioink that promotes angiogenic sprouting and neovascularization. This review aims to cover the recent progress in the field of 3D bioprinting of vascularized tissues. It will cover the methods of bioprinting vascularized constructs, bioink for vascularization, and perspectives on recent innovations in 3D printing and biomaterials for the next generation of 3D bioprinting for vascularized tissue fabrication.

Keywords: 3D printing; Bioink; Bioprinting; Tissue engineering; Vascularization.

Figure 1

Printing strategies applied to vascularized tissue fabrication. Indirect printing involves printing of a mold or sacrificial component for subsequent cell seeding. Direct printing is performed with cell-loaded or cell-only bioink for desired bioprinted patterning. A combination of indirect and direct bioprinting can be used for vascularized tissue constructs, such as to fabricate larger channels for cell seeding and connecting cellularized patterns for capillary network self-assembly. Adapted with permission from Tan et al 2014 [109] and Lee et al 2014 [54].

Figure 2

3D extrusion bioprinting for microchannel filaments. (A) Coaxial extrusion bioprinting allows for direct printing of a scaffold with endogenous microchannels. (B) A multilayered construct with a cross-section inlay shows embedded microchannels with relevant dimensions. Adapted with permission from Gao et al. 2015 [24].

Figure 3

Indirect printing of perfusable vascular network. (A and B) Pluronic F127 is printed into a supporting gel bath (matrix and fluid filler) of Pluronic F127-diacrylate. (C) Photopolymerization covalently crosslinks support gel. (D and E) Unmodified Pluronic F127 is liquefied at low temperatures and vacuumed out to leave a perfusable vascular network (F). Adapted with permission from Wu et al. 2011 [123].

Figure 4

Inkjet strategies for 3D bioprinting. Alginate can be printed in a calcium-containing solution or substrate for layer-by-layer fabrication. Adapted with permission from Nakamura et al. 2008 [77].

Figure 5

Alternative 3D printing method for tissue construct vascularization. (A) Direct printed carbohydrate glass lattices (green) are embedded in cell-loaded bioink and dissolve after perfusion, leaving behind perfusable channels (red). (B) Precise, resolute channels can be fabricated with (C) open interchannel junctions (inlay) and endothelialized with HUVECs. Adapted with permission from Miller et al. 2012 [71].

Figure 6

Use of cell-free bioink to promote cellular integration. (A) Indirect printing was used with cell-free bioink (i.e., collagen) around a sacrificial gelatin channel. (B) The collagen channel provided a biocompatible surface for endothelialization and (C) supported angiogenic sprouting. Adapted with permission from Lee et al. 2014 [53].

Figure 7

Cell loaded bioink for use in vascularized tissue constructs. (A) Combinatorial approach combines perfusable channels with direct printing of vascular support cells (i.e., fibroblasts) supported by a photocurable matrix (i.e., gelatin methacrylate). (B) Fibroblasts are bioprinted to support HUVEC channels and provides proof-of-concept for tissue-specific cell type organization. Adapted with permission from Kolesky et al. [46].

Figure 8

Multi-scaled approach for vascular fabrication. (A) Indirect printing of channels using cell-free bioink is advanced by using cell-loaded bioink to deliver vascular cell types. (B) HUVECs assemble into capillary network and connect with perfused channels. Adapted with permission from Lee et al. 2014 [54].

Figure 9

Cell-only bioink for vascularized tissue fabrication. (A) Bioprinting allows for precise organization of cell aggregates to facilitate a variety of vessel formation strategies. (B) Bioprinting cell spheroids around agarose support structures demonstrate vessel formation through cellular self-assembly. Adapted with permission from Mironov et al. 2009 [73] and Norotte et al. 2009 [82].

Figure 10

Proposed 3D bioprinting strategy for vascularized tissue fabrication. Combining 3D extrusion printing with cell-directing materials would provide for a multi-scaled approach for tissue assembly. Layer-by-layer, cell-specific positioning guides large-scale design, and cell-directing materials support vascularization post-printing.