Poly(ethylene glycol)-Norbornene as a Photo-Click Bioink for Digital Light Processing 3D Bioprinting
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Digital light processing (DLP) bioprinting is an emerging technology for 3D bioprinting (3DBP) owing to its high printing fidelity, fast fabrication speed, and higher printing resolution. Low viscosity bioink such as poly(ethylene glycol) diacrylate (PEGDA) is commonly used for DLP-based bioprinting. However, the crosslinking of PEGDA proceeds via chain-growth photopolymerization that displays significant heterogeneity in crosslinking density. In contrast, step-growth thiol-norbornene photopolymerization is not oxygen inhibited and produces hydrogels with an ideal network structure. The high cytocompatibility and rapid gelation of thiol-norbornene photopolymerization has lend itself to the crosslinking of cell-laden hydrogels but has not been extensively used for DLP bioprinting. In this study, we explored 8-arm PEG-norbornene (PEG8NB) as a bioink/resin for visible light initiated DLP-based 3DBP. PEG8NB-based DLP resin showed high printing fidelity and cytocompatibility even without the use of any bioactive motifs and high initial stiffness. In addition, we demonstrated the versatility of PEGNB resin by printing solid structures as cell culture devices, hollow channels for endothelialization, and microwells for generating cell spheroids. This work not only expands the selection of bioinks for DLP-based 3DBP, but also provides a platform for dynamic modification of the bioprinted constructs.