Fig. 7.

(A) Different types of polymer chain, crosslinker, and cells for developing cell-incorporated inks based on PEG. (B) Ink configuration after lightly and heavy crosslinking of PEG. (C) Three-dimensional printing strategy of developed PEG ink. Secondary crosslinking may be applied for heavily crosslinking the polymer chains after the 3D printing process was completed. (D) Photograph of 3D printed structures using PEG-gelatin bioinks (scale bar ​= ​500 ​μm). (E) Examples of combined 3D bioprinting of PEG-gelatin (red) and PEG-fibrinogen (blue) bioinks in spheroidal and grid designs and (F) cell viability results associated with using 3 w/v% fibrinogen in PEG, PEG-PEG, and PEG-gelatin (scale bar ​= ​200 ​μm). Human umbilical vein endothelial cells (HUVECs) seeded with human MSCs, which filled the pore spaces in the internal structure. Reproduced from Rutz et al. [87] with permission from WILEY-VCH Verlag GmbH & Co. PEG, polyethylene glycol; MSC, mesenchymal stem cell.