**3. Conclusion**

The spatiotemporal nature of cadherin-based cell–cell adhesions enables cells to self-sort, assemble into tissues, or can lead to cellular differentiation. However, these adhesions cannot be exogenously controlled, and as such make the construction of bottom-up tissues difficult to manage. Chemical means for binding cell membranes together are too rigid and offer limited reversibility. There is also a lack of spatiotemporal control. However, light is non-invasive, highly biocompatible, and can be delivered in a spatiotemporal fashion. Through the delivery of optogenetic proteins to the cell membrane, the construction of spatiotemporal cell–cell adhesions has been achieved. These proteins can respond to a wide range of wavelengths enabling the use of multiple pairs to construct larger structures, form reversible adhesions, and offer superior kinetics to other adhesion methods.
