Digital light processing (DLP) bioprinting can be used to fabricate volumetric scaffolds with intricate internal structures, such as perfusable vascular channels. The successful implementation of DLP bioprinting in tissue fabrication requires using suitable photo‐reactive bioinks. Norbornene‐based bioinks have emerged as an attractive alternative to (meth)acrylated macromers in 3D bioprinting owing to their mild and rapid reaction kinetics, high cytocompatibility for in situ cell encapsulation, and adaptability for post‐printing modification or conjugation of bioactive motifs. In this contribution, the development of gelatin‐norbornene (GelNB) is reported as a photo‐cross‐linkable bioink for DLP 3D bioprinting. Low concentrations of GelNB (2–5 wt.%) and poly(ethylene glycol)‐tetra‐thiol (PEG4SH) are DLP‐printed with a wide range of stiffness (G' ≈120 to 4000 Pa) and with perfusable channels. DLP‐printed GelNB hydrogels are highly cytocompatible, as demonstrated by the high viability of the encapsulated human umbilical vein endothelial cells (HUVECs). The encapsulated HUVECs formed an interconnected microvascular network with lumen structures. Notably, the GelNB bioink permitted both in situ tethering and secondary conjugation of QK peptide, a vascular endothelial growth factor (VEGF)‐mimetic peptide. Incorporation of QK peptide significantly improved endothelialization and vasculogenesis of the DLP‐printed GelNB hydrogels, reinforcing the applicability of this bioink system in diverse biofabrication applications.

Decellularized small intestine submucosa (dSIS) is a promising biomaterial for promoting tissue regeneration. Isolated from the submucosal layer of animal jejunum, SIS is rich in extracellular matrix (ECM) proteins, including collagen, laminin, and fibronectin. Following mild decellularization, dSIS becomes an acellular matrix that supports cell adhesion, proliferation, and differentiation. Conventional dSIS matrix is usually obtained by thermal crosslinking, which yields a soft scaffold with low stability. To address these challenges, dSIS is modified with methacrylate groups for photocrosslinking into stable hydrogels. However, dSIS has not been modified with clickable handles for orthogonal crosslinking. Here, the development of norbornene‐modified dSIS, named dSIS‐NB, via reacting amine groups of dSIS with carbic anhydride in acidic aqueous reaction conditions is reported. Using triethylamine (TEA) as a mild base catalyst, high degrees of NB substitution on dSIS are obtained. In addition to describing the synthesis of dSIS‐NB, its adaptability in orthogonal hydrogel crosslinking for cancer and vascular tissue engineering is explored. Impressively, compared with physically crosslinked dSIS and collagen matrices, orthogonally crosslinked dSIS‐NB hydrogels supported rapid dissemination of cancer cells and superior vasculogenic and angiogenic properties. dSIS‐NB is also exploited as a versatile bioink for 3D bioprinting.

Human umbilical vein endothelial cells (HUVECs) and human aortic smooth muscle cells (HASMCs) were coaxially and continuously extruded without ultraviolet illumination using a microfluidic-based nozzle. Type I collagen (3 mg ml ⁻¹ ) containing HUVECs and a crosslinking reagent (100 mM CaCl ₂ ) were supplied as the core material. A mixture of 3 mg ml ⁻¹ of type I collagen (25%) and 1.8% weight volume ⁻¹ of sodium alginate (75%) was provided as the shell layer material surrounding the core material. The HUVECs were well proliferated at the core and reshaped into a monolayer formation along the axial direction of the scaffold. The HASMCs showed more than 90% cell viability in the shell layer. Fluorescent beads were passed through the inside channel of the scaffold with the HUVEC core and HASMC shell using an in-house connector. This double-layered scaffold showed higher angiogenesis in growth factor-free medium than the scaffold with only a HUVEC core. The HASMCs in the shell layer affected angiogenesis, extracellular matrix secretion, and outer diameter. The proposed technique could be applied to three-dimensional bioprinting for the production of high-volume vascularised tissue.

One of the most promising techniques for treating severe peripheral artery disease is the use of cellular tissue-engineered vascular grafts (TEVGs). This study proposes an inverse-gravity (IG) extrusion technique for creating long double-layered cellular TEVGs with diameters over 3 mm. A three-layered coaxial laminar hydrogel flow in an 8 mm-diameter pipe was realised simply by changing the extrusion direction of the hydrogel from being aligned with the direction of gravity to against it. This technique produced an extruded mixture of human aortic smooth muscle cells (HASMCs) and type-I collagen as a tubular structure with an inner diameter of 3.5 mm. After a 21 day maturation period, the maximal burst pressure, longitudinal breaking force, and circumferential breaking force of the HASMC TEVG were 416 mmHg, 0.69 N, and 0.89 N, respectively. The HASMC TEVG was endothelialised with human umbilical vein endothelial cells to form a tunica intima that simulated human vessels. Besides subcutaneous implantability on mice, the double-layered blood vessels showed a considerably lower adherence of platelets and red blood cells once exposed to heparinised mouse blood and were considered nonhaemolytic. The proposed IG extrusion technique can be applied in various fields requiring multilayered materials with large diameters.

Generating functional and perfusable micro-vascular networks is an important goal for the fabrication of large and three-dimensional tissues. Up to now, the fabrication of micro-vascular networks is a complicated multitask involving several different factors such as time consuming, cells survival, micro-diameter vasculature and strict alignment. Here, we propose a technique combining multi-material extrusion and ultrasound standing wave forces to create a network structure of human umbilical vein endothelial cells within a mixture of calcium alginate and decellularized extracellular matrix. The functionality of the matured microvasculature networks was demonstrated through the enhancement of cell–cell adhesion, angiogenesis process, and perfusion tests with microparticles, FITC-dextran, and whole mouse blood. Moreover, animal experiments exhibited the implantability including that the pre-existing blood vessels of the host sprout towards the preformed vessels of the scaffold over time and the microvessels inside the implanted scaffold matured from empty tubular structures to functional blood-carrying microvessels in two weeks.