Improved resolution and fidelity of droplet-based bioprinting by upward ejection

Bioprinting has emerged as a powerful biofabrication technology with widespread applications in biomedical fields because of its superiority in high-throughput, high-precision, 3D structure fabrication. For bioprinting, two of the most important parameters are the printing precision (i.e., droplets resolution) and structural fidelity (i.e., conformity of the printed objects to the design). The major factors that hinder resolution and fidelity are gravity and impact force between printed droplets and substrate. However, existing solutions to these two issues, including decreasing droplet volume and introducing sacrificial materials, cause other problems, such as complexity or poor biocompatibility. Here, we reported a variant 3D bioprinting technique, termed as upward bioprinting, in which the nozzle of bioprinter is overturned and the ejection direction is opposite to gravitational force. Employing this technique, we fabricated discrete droplets, continuous lines, and 3D multilayer constructs using algina...