The velocities for each colony were tracked throughout the experiment. Notably, analysis of Volvox motion over time showed that only targeted cells saw clear changes in velocity (slowing down) when illuminated in a punctuated fashion (Figure 2h, Supplementary Movie 4). However, wide variability in the effect of the light pulses was also observed, with more motile Volvox tending to be more strongly inhibited by the light. This heterogeneity is unavoidable in biological systems, further strengthening the need for tailored control of individual agents made possible using the DOME.

Discussion

One of the primary aims of the DOME is to provide an accessible platform for optical interacting with microscale agents. While comparative systems have been proposed previously, none provide a fully integrated device and most provide little to no documentation to aid reproducibility. The DOME is truly open source in nature, with the STL files required to fabricate the device available online along with protocols detailing the computational set up. In addition, a video tutorial showing the step by step construction process is available. The DOME is operated using control scripts written in Python on a Raspberry Pi interface, making it a highly accessible platform even for users with little or no programming experience. At £685, the cost associated with the DOME is also low compared with other comparable systems.

Conclusion

In summary, the DOME offers a versatile and low-cost platform for the engineering of microscopic collectives using light. The basic building blocks of local communication, stigmergy, and controllable motion demonstrated could be used as the basis for more complex collective behaviours. Entirely new swarm behaviours could even be engineered by combining the closed loop nature of the DOME with automatic discovery processes based on machine learning algorithms \cite{Jones_2019,cichos2020machine,Sol__2018}. The DOME’s open-source modular design makes it easy to adapt for new needs, for example, changing the light source of the projector to enable different forms of fluorescent imaging, different magnification, or adding temperature/gas control to maintain the viability of different types of cell (e.g. mammalian cells), and future extensions could even introduce magnetic, sound, or chemical inputs as additional control modalities. Beyond microswarm engineering, the DOME also offers a means to both understand and influence the collective behaviour of natural cellular populations, opening up new avenues for the study of complex systems spanning cancer to the microbiome.