Cell aggregates as self‐assembling bioink

Understanding the principles of biological self‐organization is indispensable for developing efficient strategies to build living tissues and organs. Morphogenesis, the sequence of natural pattern‐forming processes through which organs acquire their final shape, is under strict genetic control. However, genes do not create spatial structures: physical mechanisms do. Here we show how the self‐assembly capacity of cells and tissues can be exploited to construct living structures of prescribed shape. The central tenet of our approach is that tissues composed of motile and adhesive cells mimic the behavior of liquids. To biologically validate this idea, we first show that the fusion of embryonic cushion tissue during heart morphogenesis proceeds similarly in vitro and in vivo and both qualitatively and quantitatively resembles the coalescence of liquid drops. Next, we demonstrate that, once given the right initial cues, that is directed, spherical cell aggregates mixed with appropriate hydrogel behave as self‐assembling “bio‐ink” particles. Finally, we show that these bio‐ink particles can be dispensed by special “bio‐printers.” We print cellular toroids, tubes and in particular “beating” sheets of cardiomyocytes.