Although heat-assisted DLP allowed the fabrication of PEG hydrogels with much stronger mechanical properties compared to traditional molding or "with-water" 3D printing, their maximal stress remained quite low for the most of elastic ones based on high MW PEG (e.g., 0.6-0.7 MPa for PEGDMA 8k). To improve their mechanical properties by promoting hydrogen bonding, PEG 6000 functionalized with bidirectional carboxylic groups (PEGCOOH, Figure ) was added to the resin. The addition of 5% PEGCOOH increased the mechanical strength of the hydrogels by about 25%. However, the positive impact of hydrogen bonding vanished upon further increasing the amount of PEGCOOH (Figures and), likely because of the decrease in crosslinking density.