Void‐Free 3D Bioprinting for In Situ Endothelialization and Microfluidic Perfusion

Abstract

Two major challenges of 3D bioprinting are the retention of structural fidelity and efficient endothelialization for tissue vascularization. Both of these issues are addressed by introducing a versatile 3D bioprinting strategy, in which a templating bioink is deposited layer-by-layer alongside a matrix bioink to establish void-free multimaterial structures. After crosslinking the matrix phase, the templating phase is sacrificed to create a well-defined 3D network of interconnected tubular channels. This void-free 3D printing (VF-3DP) approach circumvents the traditional concerns of structural collapse, deformation, and oxygen inhibition, moreover, it can be readily used to print materials that are widely considered "unprintable." By preloading endothelial cells into the templating bioink, the inner surface of the channels can be efficiently cellularized with a confluent endothelial layer. This in situ endothelialization method can be used to produce endothelium with a far greater cell seeding uniformity than can be achieved using the conventional postseeding approach. This VF-3DP approach can also be extended beyond tissue fabrication and toward customized hydrogel-based microfluidics and self-supported perfusable hydrogel constructs.

Expanding and optimizing 3D bioprinting capabilities using complementary network bioinks

“…The only classes of biomaterials that should pose difficulties are those that cannot be made miscible with gelatin and those that rely on an opposing thermal gelation (e.g., poloxamer 407). We have also used a very standard thermal extrusion–based approach that is compatible with existing 3D bioprinting methods ( 11 , 23 , 29 ). Together, these design factors should enable complementary network bioinks to find broad applicability across different biomaterial systems and 3D printing protocols, and provide new opportunities for biofabrication and tissue engineering.…”

Printability and Shape Fidelity of Bioinks in 3D Bioprinting

“…Like in conventional 3D printing, support materials, in the form of stiff hydrogels, 228 ceramics, 33 , 176 , 229 or thermoplastic polymers, 31 , 33 , 55 can be included to provide long-lasting structural fidelity to constructs based on bioinks displaying low mechanical properties. Likewise, sacrificial materials e.g., based on thermosensitive hydrogels (e.g., gelatin 230 − 232 or poloxamers 101 , 233 , 234 ) or alginate, 235 , 236 can be used to print temporary supports. 234 The effect of gravity on printed filaments, as well as that of deformation due to time-dependent flow prior to cross-linking can be countered by printing within an environment providing buoyancy or direct support to the bioink, for instance via suspended printing into support bath, made of shear-thinning polymers, fluidized gels, or granular media, as reported for example with the approach termed freeform reversible embedding of suspended hydrogels, or FRESH.…”

Tailoring Gelation Mechanisms for Advanced Hydrogel Applications

“…As a cytocompatible material, the gelatin bioink could be preloaded with endothelial cells to form uniform vascular networks without needing to postseed cells into channels. [ 237 ]…”