Phototactic microswimmers in pulsatile flow: Toward a novel harvesting method

Area of Science:

• Biophysics
• Microfluidics
• Cell Separation

Background:

• Motile algae separation is crucial for biofuel production and environmental applications.
• Traditional separation methods often require mechanical components or chemical additives.
• Understanding microswimmer behavior in controlled flow is key to developing efficient separation techniques.

Purpose of the Study:

• To investigate the advantages of pulsatile flow over steady flow for separating motile algae cells.
• To elucidate the underlying mechanism coupling phototaxis and flow dynamics for enhanced separation.
• To assess the potential for extending this technique to other active particles and applications.

Main Methods:

• Utilized a double Y-microchannel setup to study algae cell separation.
• Implemented controlled pulsatile and steady flow conditions.
• Applied light stimulation to induce phototactic behavior in *Chlamydomonas reinhardtii*.
• Performed numerical simulations to model particle behavior under external fields.

Main Results:

• Pulsatile flow significantly improved the separation index (SI) for motile algae compared to steady flow when light was applied (75% vs. 65%).
• In the absence of light, pulsatile flow offered no advantage over steady flow, with SI around 50%.
• The study demonstrated that the separation mechanism is tunable by flow pulsation and external stimuli.

Conclusions:

• Pulsatile flow, coupled with phototaxis, offers an effective, non-mechanical method for enhancing microalgae separation.
• The findings suggest broader applicability for controlling and separating active particles in microfluidic devices.
• This approach presents a promising alternative for algae harvesting and other bioseparation processes.