Biocompatibility of the hybrid hydrogels was further examined through a comparative cytocompatibility study in 3D, where HepG2 cells were encapsulated in the hybrid hydrogels and cultured over a period of 14 days (Figure ), followed by live/dead staining. The additional loading of bPEs in GelMA hydrogels increased the overall network density and, together with the cell-repellant properties of PEO , resulted in lower viability of HepG2 cells in hybrid hydrogels, in particular during the first days of cultivation. However, despite PEO constituting the largest proportion of the GelMA/bPE hydrogels by several times, HepG2 viability was still markedly higher as compared to most PEO-based hydrogels. For example, we have previously demonstrated that PEGMA/PEGDMA hydrogels that do not expose any bioactive sites yielded cell viability around 10% only. However, when supplemented with 1.25% GelMA, viability remarkably increased to over 60% . Furthermore, we did not observe agglomeration or spheroid formation of HepG2 cells as it usually occurs in PEO hydrogels . The GelMA content in the GelMA/bPE hybrid hydrogels is posited to be high enough to offer sufficient adhesion sites (RGD) to cells. From the homogenous cell distribution in the hydrogels (Figure ), we furthermore conclude that GelMA chains were uniformly distributed in the inter-domain space of the polyelectrolyte complex domains, thus rendering RGD sites easily accessible to cells.