Numerous promising GelMA/bPE ink formulations were identified by the small amplitude oscillatory strain measurements. Among these, we limited our investigation to formulations wherein the properties of the static bulk material prior and after extrusion were also optimal for biofabrication. Hence, rheological parameters describing the shear conditions present during extrusion through a small orifice, including yield stress, complex viscosity, and post-shearing recovery, of the 37 °C GelMA/bPE inks were further examined and compared to the rheological performance of 22 °C GelMA inks. The yield stress for a material is defined as the minimum stress required to initiate its flow, and thus influences the required extrusion pressure in 3D printing. In a stress ramp experiment, yielding occurs when an initially elastic material, exhibiting stressindependent viscosity (plateau-region), displays a steep decrease in viscosity (viscosity-drop region) above a characteristic stress threshold (Figure , S8). It is primarily observed for entangled polymer networks or physically pre-crosslinked materials, where non-covalent bonds must first be broken to enable macroscopic flow. A large yield stress of an ink generally promotes syringeability and fiber formation during extrusion as well as post-printing shape fidelity (i.e., no flow in absence of applied force) . However, if the yield stress exceeds a critical value, it can impede dispensing, hinder miscibility with cells, and negatively impact cell viability because of the high pressure that is needed for extrusion .