in cell biology, [ 29,30 ] e.g., in cell signaling and protein expression. [31][32][33] For instance, it is reported that shear stress promotes maturation of megakaryocytes. [ 34 ] Moderate shear stress was found to have an infl uence on stem cell differentiation. [ 35 ] Excessive shear stress, in contrast, even dispatches cells by disrupting the membrane. These phenomena are even more crucial in bioprinting processes, where hydrogels of high viscosity and small nozzles are applied in an attempt to improve the fi nal printing resolution. Here, we show that both hydrogel viscosity and nozzle size directly affect shear stress. To prevent adverse cell response and printing-related cell death, it is essential to control the shear stress level, identify its most important drivers, and study the cell response upon different stress levels. We hypothesize that regulating shear stress and elucidating its impact would be of great use in balancing cell integrity and printing resolution.We present a microvalve-based bioprinting system for the manufacturing of high resolution, multi-material 3D structures ( Scheme 1 A). Applying a straightforward fl uid-dynamics model, we were able to precisely control shear stress at the nozzle site, which could be adjusted by varying the printing pressure, hydrogel viscosity, and the nozzle diameter. Using this system, we conducted a broad study on how cell viability and proliferation potential are affected by different levels of shear stress (Scheme 1 B). Generating complex, multi-material 3D-structures, we demonstrate that high-resolution printing at moderate, cell-friendly nozzle shear stress are not mutually exclusive.The printer used throughout this study comprised four microvalve-based print heads, each individually controllable and heatable, mounted to a three-axis robotic system ( Figure S1, Supporting Information). A metal stage that could be lowered into a container fi lled with a bi-phasic support liquid-perfl uorocarbon (PFC) and an aqueous crosslinker solution-was used as a printing platform that allowed for the manufacturing of macroscopic, multi-layered 3D structures ( Figure S1, Supporting Information). The presented printing system dispenses single drops of cell-hydrogel suspension by jetting using electromagnetic microvalves. Thus, cells are primarily exposed to mechanical stress in the form of shear stress. To describe the shear stress condition in the nozzle of the valve, we developed a fl uid dynamics model for transient fl ow of non-Newtonian fl uids (hydrogels) based on the Bernoulli equation for unsteady fl ow: Equation (