After the ink is extruded, UV irradiation is used to trigger free radical polymerization to form the hydrogel network. For solid viscoelastic materials, rheology can again be used to measure the storage modulus of the material. The storage modulus indicates the stiffness of the material, and the Young's modulus can be approximated using the storage modulus, as the Young's modulus is approximately three times larger than the storage modulus for rubber-like materials. In Figure , we show the storage modulus for each ink at increasing angular frequencies, which demonstrates the stability of the material. Reduced crosslinking is expected to reduce material stiffness, and we indeed measure a much lower storage modulus for the low BIS content hydrogel. The higher BIS content inks, however, quickly reach crosslinking saturation, and no significant difference in stiffness is measured between 0.7 wt%, 1.0 wt%, and 1.3 wt% BIS hydrogels. These results suggest that, while crosslinker content is ideal for tuning hydrogel stiffness, stiffness cannot be further increased using BIS once this maximal crosslinking is reached. A trend of increasing stiffness comes from increasing MC content, with only a small effect compared to BIS and PEDOT:PSS. The PEDOT:PSS content has a very large influence on storage modulus, but the opposite trend of MC and BIS is recorded: the higher PEDOT:PSS content hydrogels have lower storage moduli. Although we suspected that the dark color of PEDOT:PSS may have prevented crosslinking, thus resulting in lower stiffness, we found that the impact of PEDOT:PSS on crosslinking time seems minimal for the concentration range and conditions presented. Instead, we propose that the increased content of unaligned polymers in the double network system results in fewer elongated polymers and decreased stiffness. While the stability of most hydrogels remains relatively constant as angular frequency increases, the highest PEDOT:PSS content hydrogel (2.0 wt%) shows the greatest change at increasing angular frequencies, indicating that increased PEDOT:PSS results in less stability. Stiffness can additionally be assessed using tensile characterization. The slope of the stressstrain plot can also indicate Young's modulus, the shape of the plot can reveal material behavior, and the material's maximum strain can be indicated by the breaking point. We 3D printed a band (dimensions: width -10 mm, thickness -0.6 mm, length -30 mm) of each hydrogel material to assess the tensile behavior (Figure ). The various BIS and MC hydrogels demonstrate similar trends as revealed with during the rheological assessment. The 0. process, an effect that has been previously observed from extrusion printed PEDOT:PSS. For the rheological assessment, the hydrogel is essentially in a cast mold, sandwiched between the platform and the rotational plate, when it is polymerized. The PEDOT:PSS polymer networks can have a random alignment in this method, and are not likely to be extended. During extrusion printing, the shear forces likely align the fiber network. Using this method, the aligned fibers are already somewhat elongated, limiting the material's ability to stretch and reinforcing the printed structure.