Pattern formation occurs spontaneously in endothelial cell cultures, leading to the formation of capillary networks, which eventually grow to form blood vessels. This phenomenon occurs on a time scale of a few days. We show here that patterns can also be induced on a much shorter time scale, by using the Faraday hydrodynamic instability, resulting from an oscillatory motion of the container. Close to the threshold of instability, the patterns observed are very sharp concentric rings or stripes. The patterns can be induced only inside a very narrow time window, ~ 5 min. Cells attachment then develops, and pattern formation can no longer be induced. The time window for pattern formation was diminished by favoring cell attachment, for instance by treating culture dishes with cationic macromolecules, such as poly-L-Lysine. It was increased by cooling the cells to 18°C, or by a prolonged exposure of the cells to trypsin, which is known to digest adhesion molecules. The Faraday instability leads to a method to characterize cell attachment. It also permits the production of heterogeneous cultures with several cell types, with a well controlled heterogeneity. This can be used to study heterotypic cell interactions in vitro.
Pattern formation at the bicritical point of the Faraday instability
