3D printing of complex constructs. After demonstrating the high printability and the tunability of the mechanical properties of GelMA-CBP constructs, we explored the ability to print complex structures and tested the limits of each formulation. A largely untapped and exciting application of 3D bioprinting is to use materials with properties resembling those of ECM to build structures, that mimic tissues and organs. To assess the suitability of our bioinks for this application, formulations composed of the optimal concentration of 0.5% CBP and 1, 3, 5, or 7% GelMA were used to print structures at 37 ºC with increasing levels of complexity. While 0.5% CBP concentration is not the minimum that can be used for each formulation, it is a good compromise because it guarantees high printability for this range of GelMA concentrations at a constant CBP content, which simplifies the analysis and allows direct comparisons between inks printed at 37 ºC.