Yellow food dye #5 - a common food additive - is revealed as the secret ingredient in 3D printing biomaterials with complex physically entangled networks, which characterize biological tissues, according to a new report. Solid organ tissues move fluids and exchange materials through distinct yet biophysically and biochemically connected vascular networks. Engineering this vasculature in biocompatible materials used for growing tissues has been challenging. One way to create artificial structures capable of mimicking the complex vascular architecture of biological tissues, like those found inside the lung, is through a type of 3D printing called projection stereolithography. The technique uses projected light and photoreactive resins to create solid objects. Photoabsorbing additives can be used to stop undesirable photopolymerization outside of the targeted region, to ensure sufficient resolution for the creation of complex architectures. However, common chemicals used for this purpose are known genotoxic carcinogens and are not suitable for biomanufacturing. The identification of non-toxic photoabsorbers useful in projection stereolithography could overcome a major limitation in the design and generation of biocompatible hydrogels. Now, Bagrat Grigoryan and colleagues show that widely used natural and synthetic food dyes can be used as potent photoabsorbers in the production of intricate and functional vascular networks within hydrogels. Grigoryan et al. evaluated the use the food dye tartrazine, or yellow #5, a common food coloring found in a variety of snacks and beverages, as a light-blocking additive to rapidly create elaborate multivascular hydrogels. The authors demonstrate the functional capabilities of the materials through recreating biological processes, like blood cell oxygenation in the lung, for example. Furthermore, using the technique, the authors optimized bioengineered liver tissue and successfully transplanted it into a mouse model of chronic liver injury to highlight the translational potential of the method.