Pulsative flow improves control of phototactic microswimmers

With the ability to propel through their fluid environments, microswimmers and microrobots represent enormous potential in biotechnology and biomedicine, including in applications such as minimally invasive surgery and targeted drug delivery. But efficiently manipulating the flow of their surroundings in a way that “delivers” them with any measure of precision has been a longstanding challenge.

In a promising new study, Minh et al. demonstrated the advantages of pulsatile flow for separating phototactic algae cells – whose movements are triggered by light – and directing them towards a target. After first characterizing the phototactic behavior of the microalgae strain, the scientists used a double Y-microchannel to examine cell separation in a steady regime at different flow rates and a pulsatile regime at different frequencies. For each flow regime, they conducted experiments with and without phototaxis.

“Each period of a pulsatile flow is composed of two parts: low flow (LF) and high flow (HF),” said author Mojtaba Jarrahi. “LF represents the half of the period where the flow rate is less than the mean value. During this phase, the phototactic microswimmers are less advected by the flow and they can perceive the light situation and thus be redirected by external stimulation (light) to a desired direction. Then, during the rest of the cycle (HF), the flow effects become dominant, driving the microswimmers towards the target.”

Additionally, the team posited that their findings may extend to other active particles stimulated by an attractive or repulsive external field.

“The potential applications can go beyond algae harvesting to the control and enhancement of separation or accumulation processes without using any mechanical component or chemical substance,” said Jarrahi.

Source:“Phototactic microswimmers in pulsatile flow: towards a novel harvesting method,” by Chau Nguyen Minh, Hassan Peerhossaini, and Mojtaba Jarrahi, Biomicrofluidics (2022). The article can be accessed at https://doi.org/10.1063/5.0097580 .