**2.5 Regulation of cell sorting using photoswitchable cell–cell adhesions**

Different types of photoswitchable cell–cell adhesions can be mixed to obtain cell sorting within multicellular mixtures and organize cells as predicted by the DAH. For example, when cells expressing Vivid or Cph1 at their cell surface were mixed and illuminated with either blue or red-light clusters of cells with Vivid or Cph1 cells formed, respectively. When both blue and red light was used self-isolated clusters containing either Vivid or Cph1 cells were observed (**Figure 4**) [57]. That means that the adhesive force for Vivid and Cph1 is lower than that for the homodimers formed for each system due to the specific protein–protein interactions. Similarly, also different pairs of heterophilic cell–cell adhesions can be used to achieve self-sorting in mixtures containing four different cell types. In mixtures of iLID, Nano, nMag, and pMag expressing cells, two types of multicellular aggregates assembled each containing one of the protein pairs (iLID/Nano or nMag/pMag) [62]. It should be noted that cell sorting is only possible if the system is under thermodynamic control and is not observed if kinetically trapped structures form. Therefore, mixtures of iLID, Nano, nMagHigh and pMagHigh do not sort into distinct clusters.
