Entanglement-enhancing inks enable rapid vat-photopolymerization 3D bioprinting of physically robust hydrogel constructs

Light-based vat-polymerization has become a leading technique in engineering tissue constructs. However, it remains challenging for the rapid fabrication of hydrogel constructs with high structural fidelity, particularly at ultralow polymer concentrations required to mimic the physiological extracellular matrix. Here, we design a solid-to-solid (STS) bioprinting system to engineer hydrogels with physically robust properties. By introducing chain entanglements into gelatin methacrylate (GelMA)-based ink, we create a pre-organized ink that can facilitate photopolymerization and significantly expand the biofabrication window. After fabrication, the engineered hydrogels undergo volumetric shrinkage while concurrently offering mechanical reinforcement. Furthermore, this strategy allows us to manufacture ultralow amounts of GelMA hydrogels (2.5% w/v) without compromising structural stability or fidelity while also enhancing cellular morphology and viability. We demonstrate the versatility of this approach by fabricating architectures ranging from intricate 2D patterns to complex 3D biomimetic scaffolds. Notably, compared with traditional liquid-based precursors, the STS system achieves superior resolution and curing speed. We further showcase the potential of this system by engineering prevascularized constructs, cartilage, and dental pulp. Both in vitro and in vivo assessments reveal robust tissue maturation and histological organization, highlighting its significant promise for applications in tissue engineering and regenerative medicine.