Next, we investigated the impact of PEG chain length on the mechanical strength of the printed specimens. As expected, the products printed from higher MW PEG showed greatly enhanced mechanical properties compared to those from lower MW ones. As shown in Figure , the Young's modulus of the 3D printed specimens increased from 14.8 to about 200 MPa with MW increasing from 2000 to 6000 g mol , and the maximum tensile stress reached more than 10 MPa from 0.98 MPa. A yielding point was observed with higher MW macromonomers (Figure ), indicating the plastic deformation related to the crystal phase of long PEG chains. The mechanical performance became steady upon further increase in the MW (>6000 g.mol -1 ) of PEG macromonomers. Note that the 3D printed products from PEGDA 700 were very brittle and weak, similar to that printed from PEGDMA 2k.