SPIM-Flow, an integrated light-sheet and microfluidics platform for hydrodynamic studies of Hydra

Selective plane illumination microscopy (SPIM), or light sheet, is a powerful three-dimensional imaging approach. However, access to and interfacing microscopes with microfluidics have remained challenging. Complex interfacing with microfluidics has limited the SPIM's utility in studying the hydrodynamics of freely moving multicellular organisms. We developed SPIM-Flow, an inexpensive light sheet platform that enables easy integration with microfluidics. We used SPIM-Flow to study the hydrodynamics of freely moving Hydra polyps in millimeter-sized chambers (4 mm wide, 1.5 mm height). Our initial experiments across multiple animals, feeding on a chip (Artemia franciscana nauplius used as food), and baseline behaviors (eg., tentacle swaying, elongation, and bending) indicated animals' health inside the system. SPIM enabled easy imaging of the freely moving animal and tracer beads (for fluid visualizations) inside the larger chambers. Next, using the chambers, we investigated Hydra's response to flow. Results suggest that animals responded to established flow by bending and swaying their tentacles in the flow direction. Finally, we used a previously described video analysis software (FlowTrace) to visualize path lines generated by (e.g., vortex generated) and around (e.g., due to flow) Hydra. These results demonstrated the SPIM-Flow's utility to study the hydrodynamics of freely moving animals.