RESUMEN
Hydrogels are used in many biomedical applications, including regenerative medicine and surgical training phantoms. However, the ability to shape these materials into complex anatomical structures using additive manufacturing is limited in part by their low mechanical stiffness. We developed a hydrogel 3D printer, that projects patterns directly onto a thin layer of fluid-supported hydrogel precursor, which serves as a floating, liquid projection screen. This approach avoids inadvertent adhesion that affects typical resin-based 3D printers, and enables fast, continuous printing. As a consequence, we can print smooth objects free of layering artifacts, at rates of 200 mm/h along the Z-axis. We demonstrate the versatility of our approach by printing various complex structures, including free-standing channel networks with 500 µm-thick walls, using hydrogels with a wide range of stiffness from 7 kPa to more than 4 MPa. Lastly, because the printer features a free surface, we combined it with an extruder to perform multi-material printing. We use this strategy to create centimeter-scale, cell-laden hydrogels containing channels, that help address the key nutrient supply problem in bioprinting.