In Situ Endothelialization of Free‐Form 3D Network of Interconnected Tubular Channels via Interfacial Coacervation by Aqueous‐in‐Aqueous Embedded Bioprinting

Abstract

factors as well as get rid of waste products. [7] Three-dimensional (3D) bioprinting holds great promise as a versatile tool for replicating the spatial complexity of vascularized tissues. [8,9] For example, coaxial extrusion bioprinting can be used to fabricate cell-laden hollow microfibers that function as perfusable lumens. However, 3D networks of interconnected perfusable lumens with structural complexity is as yet difficult to achieve. [10][11][12][13] Both 3D extrusion bioprinting with fugitive inks and digital light processing (DLP)-based bioprinting enable the production of 3D networks of interconnected channels, which can be post-seeded with endothelial cells. [14][15][16] However, both processes involve multiple steps including template removal, repeated cleansing, and post-seeding. [17][18][19] These post-procedures could influence the structural precision, and forfeit inherent advantages of 3D additive manufacturing, such as rapid-prototyping and simplicity. More importantly, most templated materials used in these approaches, such as Pluronic F-127 and carbohydrate glass, are either unsuitable for carrying cells, or highly toxic to cells. [20][21][22] Thus, these approaches do not support in situ seeding of cells, which requires high seeding efficiency and uniformity. [18] To circumvent the challenge of achieving both structural printability and in situ cell seeding, embedded bioprinting is

Gelation of Uniform Interfacial Diffusant in Embedded 3D Printing

“…Previous strategies to fabricate self‐supporting, vascular‐like networks have included an aqueous‐in‐aqueous embedded bioprinting method using interfacial coacervation. [ 24 ] As this strategy imposes stringent requirements on the properties of bioinks and support materials (i.e., polycations and polyanions that form complex coacervates), they are not generalizable to a broad library of materials as is possible with GUIDE‐3DP. On the other hand, recent developments in digital light processing and volumetric bioprinting have enabled the fabrication of perfusable branched channels with high resolution and tailorable architecture.…”

“…To fabricate self‐supporting tubular structures, a new paradigm is emerging that relies on control of the liquid–liquid interface between the printed ink and a support bath. In one example, complex coacervation between oppositely charged polyelectrolytes resulted in spontaneous formation of vessel‐like shells; [ 24 ] however, this technique is limited to materials that have complementary charge. In a second example, diffusion of gelation initiators from a prefabricated, sacrificial gelatin core was used to form multilayered channel walls, [ 25 ] although this technique required manual manipulation (i.e., successive immersion into gel precursor solutions) and hence was best suited for larger‐diameter structures.…”

Simple and complex coacervation in systems involving plant proteins

“…Many opportunities remain in this area and have hardly been explored yet, for example, spinning 114,115 and bioprinting, 116,117 both of which may benefit from the unique physical properties of coacervates and the sustainability of plant biopolymers.…”

Diffusion‐Based 3D Bioprinting Strategies

“…HUVECs encapsulated within the bioink formed a confluent endothelial monolayer at the coacervated membrane, reducing the permeability of the vascular-like network. [86] While this complex coacervation approach demonstrates the potential of embedded bioprinting to fabricate complex perfusable networks, it is limited to material systems that have complementary charge. To overcome this challenge, a versatile strategy, termed Gelation of Uniform Diffusant in Embedded 3D Printing (GUIDE-3DP), was developed for the fabrication of complex branched networks using a wide range of material systems (Figure 10C).…”