GelMA Synthesis and Hydrogel Preparation

As already described in a previous study, GelMA was synthesized according to a previously described protocol (Pepelanova et al., 2018). The degree of functionalization (DoF) of GelMA used in the experiments was of 50%. GelMA solutions were prepared at a concentration of 5% (w/v). The GelMA was dissolved in 50% of PBS and either 50% (v/v) FCS, HS, or hPL (hPL pH value 7.3, manufactured by German Red Cross, Blood Service NSTOB, Springe, Germany) was added (Figure 1). After dissolving all GelMA solutions in a water bath at 37°C, they were sterile filtered with 0.45 μm polyethersulfone (PES) filters and 0.1% (w/v) photoinitiator 2-Hydroxy-4′-(2-hydroxyethoxy)-2-methylpropiophenone (Irgacure 2959) was added prior to the encapsulation of cells.

Schematic representation of 3D hydrogel-based cultivation: first GelMA hydrogels were formulated with 50% FCS, 50% HS, or 50% hPL followed by cultivation in medium supplemented with 10% FCS, 10% HS, or 2.5% hPL.