Self‐organization of rat cardiac cells into contractile 3‐D cardiac tissue

The mammalian heart is not known to regenerate following injury. Therefore, there is great interest in developing viable tissue‐based models for cardiac assist. Recent years have brought numerous advances in the development of scaffold‐based models of cardiac tissue, but a self‐organizing model has yet to be described. Here, we report the development of an in vitro cardiac tissue without scaffolding materials in the contractile region. Using an optimal concentration of the adhesion molecule laminin, a confluent layer of neonatal rat cardiomyogenic cells can be induced to self‐organize into a cylindrical construct, resembling a papillary muscle, which we have termed a cardioid. Like endogenous heart tissue, cardioids contract spontaneously and can be electrically paced between 1 and 5 Hz indefinitely without fatigue. These engineered cardiac tissues also show an increased rate of spontaneous contraction (chronotropy), increased rate of relaxation (lusitropy), and increased force production (inotropy) in response to epinephrine. Cardioids have a developmental protein phenotype that expresses both α‐ and β‐tropomyosin, very low levels of SERCA2a, and very little of the mature isoform of cardiac troponin T.