A massively parallel microfluidic device for long-term visualization of isolated motile cells

Abstract

Visualizing the natural behavior of motile cells over many hours is a challenge, as cells can leave the field of view of a microscope in a matter of minutes. Many interesting cell behaviors—such as cell division, motility phenotype, cell–cell interactions, and multicellular colony formation—require hours of observation to characterize. We present a microfluidic device that traps hundreds of single motile cells in isolated chambers, thereby allowing observation over several days. This polydimethylsiloxane device features 400 circular chambers, connected to a central serpentine channel. Motile cells are loaded into these chambers through the serpentine channel. The channel is then purged with air, fluidically isolating the chambers from each other and effectively trapping the cells. We applied the device to observe the behavior of the choanoflagellate Salpingoeca rosetta. Because of its ability to live in both solitary and colonial forms, S. rosetta is a useful model organism for the study of the evolutionary origins of multicellularity. In particular, S. rosetta can take on two distinct colonial forms: chain colonies and rosette colonies. With our device, we are able to observe the formation of these colonies from single cells more easily and with higher throughput than ever before. This device has the potential to be a powerful tool for studying the long-term behavior of motile cells.

Appendix: Media retention equations

1.1 US EPA method

$$E = \frac{{0.1288 \cdot A \cdot P \cdot M^{0.667} \cdot u^{0.78} }}{T}$$

E evaporation rate (kg/min), u wind speed just above the pool liquid surface (m/s), M pool liquid molecular weight, A surface area of the pool liquid (m²), P pool liquid vapor pressure at the pool temperature (kPa), T pool liquid absolute temperature (K).

1.2 Retention bridge evaporation time

$$t = t_{\text{evac}} + \frac{{(2.21 \times 10^{11} ) \cdot l_{B} \cdot T \cdot \left( {w_{s} \cdot h} \right)^{0.78} }}{{P \cdot M^{0.667} \cdot Q_{s}^{0.78} }} - \frac{{t_{\text{evac}} \cdot Q_{\text{evac}}^{0.78} }}{{Q_{s}^{0.78} }}$$

t time for media in bridge to evaporate (min), t _evac time syringe pump set to Q _evac (min), l _B bridge length (m), T media absolute temperature (K), w _s serpentine width (m), h channel height (m), P vapor pressure of media at T (kPa), M media solvent molecular weight, QS study flow rate (mL/h), Q _evac serpentine evacuation flow rate (mL/h).