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International Journal of Bioprinting 3D bioprinted vascularized tissue models

Table 1. Major 3D bioprinting strategies for developing vascular structures
Bioprinting Descriptions Major benefit in vascularized tissue construction
strategies
Coordinated Spatial arrangement of cell-laden or cell-compatible inks Coordinated (spatially defined) patterning of desired vascular
patterning at desired locations to produce 3D cellular construct with cell sources and pro-angiogenic factors with high design
inter-connected pre-vascular networks flexibility of manipulating internal structures and porosity
throughout the construct
Sacrificial printing Deposition of a fugitive ink in any desired geometry, followed Introduction of physical architectures, such as open and
by casting and removal of sacrificial material, enabling manual inter-connected pores or perfusable micro-channels, within
cell seeding to create endothelialized channels 3D hydrogel-based constructs with high freedom on designing
channel geometries and a wide size range
Embedding Extrusion of designated ink materials into the liquid sus- Beneficial for improving printability of soft bioink and for
printing pension bath to hold the printed filaments and their desired increasing structural integrity with high design flexibility and
geometry while printing resolution
Coaxial printing Through a core/shell printing configuration, simultaneous Direct printing of freestanding tubular structure with high
extrusion of different materials to create hollow tubular struc- dimensional flexibility (e.g., diameter, wall thickness, and
tures in a single process length) in a uniform size

2. 3D bioprinting strategies to build vascularized tissue constructs. Further, through a multi-
vascular structures material printing process, spatial patterning of vascular
precursors at desired locations using cell-laden or cell-
Numerous 3D bioprinting techniques, such as inkjet-based, compatible materials as (bio)inks can produce a 3D cellular
laser-assisted, and extrusion-based ones, are being used to construct with inter-connected pre-vascular networks.
develop multi-scale vascular structures. The fundamental For example, Jang et al. developed multi-cellular and
[26]
principles and characteristics of prevailing bioprinting multi-layered constructs through the 3D spatial patterning
techniques have already been extensively reviewed of vessel-forming cell sources and pro-angiogenic
elsewhere [22-25] . Among these prevailing techniques, growth factors to achieve a pre-vascularized cardiac
extrusion-based bioprinting is widely employed to patch, resulting in improved cell–cell interaction and
fabricate complex hierarchical vascular structures. Thus, differentiation as well as vascularized tissue regeneration.
here we focus on the application of extrusion-based Maiullari et al. presented a multi-cellular 3D bioprinting
[27]
bioprinting methods. In extrusion-based bioprinting, approach to fabricate heterogeneous vascularized cardiac
cells are encapsulated in an exogenous biomaterial ink tissue by tailoring the spatial organization of the two cell
(i.e., hydrogel), which acts as the supporting matrix. types, which can facilitate enriched vascular networks.
According to the programmed G-code, the designated Bioprinted constructs with pre-patterning of vascular
3D tissue structure can be created. Once the printing precursors can possibly use paracrine signals to enhance
process is completed, the cell-laden construct undergoes cell–cell communication and differentiation capacity,
solidification to retain its desired shape. The extrusion- thereby improving the vascularization of the engineered
based method is preferred over other bioprinting methods tissue.
owing to its ability to utilize a broad library of biomaterials
with high-viscosity inks at a higher cell density. In this Employing the coordinated pattering strategy is
section, we outline the prominent extrusion-based beneficial for the precise spatial localization of desired
bioprinting strategies and elaborate on their principles for cell types and bioactive molecules and provides high
vascularized tissue fabrication (Table 1). design flexibility by allowing the manipulation of internal
structures and porosity throughout the construct.
However, the integrated processing of multiple materials
2.1. Coordinated patterning poses technical drawbacks, such as cross-compatibility
Coordinated patterning strategy refers to the subsequent between the materials and rapid solidification for stable
process of extruding at least one cell-containing ink and one construction, all of which require continuous efforts in
biomaterial ink by iteratively switching between different advancing bioprinting techniques and biomaterials.
printing heads and spatially pattering them on demand.
Based on the primary mechanisms of vasculogenesis and 2.2. Sacrificial bioprinting
angiogenesis in the formation of vascular networks , As a top-down approach, sacrificial bioprinting deposits a
[9]
coordinated (spatially defined) patterning of vascular fugitive material in any desired geometry and subsequently
cell sources and pro-angiogenic factors allows to build casts it onto another hydrogel. “Sacrificial” ink materials

Volume 9 Issue 5 (2023) 17 https://doi.org/10.18063/ijb.748