Uv box

Gelatin methacrylate was synthesized according to previously published methods (Kuo et al. 2016 ). Type A porcine skin gelatin (Millipore Sigma, St. Louis, MO, USA; 300 bloom) was mixed at 10% (w/v) into phosphate buffered saline (PBS; Thermo Fisher) at 50 °C for 20 min. Methacrylic anhydride (MA; Millipore Sigma) was added at the ratio of 0.6 g MA/g gelatin under rigorous stirring for an hour. The reactants were then diluted 2-fold with PBS to stop the reaction. After centrifugation, the pellet was discarded and the supernatant was dialyzed against deionized water using dialysis cassettes (10 kDa MWCO, Thermo Fisher) for at least 3 days at 50 °C to remove salts and excess MA. The dialyzed GelMA was then lyophilized and kept at −80 °C for long-term storage. To form samples, GelMA was rehydrated in PBS for 10 min at 50 °C. Photoinitiator (2-hydroxy-1-(4-hydroxyethoxy)phenyl)-2-methyl-1-propanone (BASF Corp, Southfield, MI, USA) was then added into the GelMA solution at a concentration of 0.5% (w/v). If needed, cells were added at this point, and the prepolymer solution was UV cured into the desired shape for 1 min (0.09 mW/cm²) using a UV box (VWR, Radnor, PA, USA).

We designed the bioprinted placenta model (BPM) based on previous published work (C.-Y. Kuo et al., 2018 (link); C. Y. Kuo et al., 2016 ). The bioprinted placenta model is a gelatin-based, cylindrical hydrogel (diameter = 10 mm; height = 2 mm) with an patent central lumen (diameter = 1 mm; height = 2 mm) to model the spiral arteriole (1–2 mm in diameter (Jackson, Mayhew, & Boyd, 1992 (link))). All bioprinting work was completed using a commercial 3D bioprinter (3D-Bioplotter; EnvisionTEC). To prepare the prepolymer solution, lyophilized GelMA was dissolved in complete endothelial growth media at 50°C for 20 minutes. Photoinitiator (2-hydroxy-1-(4-(hydroxyethoxy)phenyl)-2-methyl-1-propanone; Irgacure 2959; BASF) was then added into the GelMA solution at 0.1% (w/v) at 50°C for 15 minutes. The prepolymer solution was loaded into the low-temperature printer head and allowed to equilibrate for 20 minutes at 37°C. Fibronectin (50 μg/mL), HUVEC (10 million/mL), and/or extravillous trophoblast (HTR8, 2 million/mL) were then added. The final enriched prepolymer solutions were then loaded into printing cartridge and allowed to equilibrate to printing temperature (e.g. ~21°C) for another 30 minutes prior to printing. Printed constructs were UV-cured for 30 seconds (0.09 mW/cm²) using a UV box (VWR).