Investigating chemotaxis in asymmetric liposomes*

Active systems have gained significant interest across various scientific disciplines. Active motion is an important phenomenon in nature, particularly when related to concentration gradients, a behavior known as chemotaxis. Examples include the directed movement exhibited by bacteria and neutrophils, orchestrated through intricate signaling pathways. In synthetic systems, active and chemotactic behavior has been demonstrated in Janus particles and colloidal structures such as polymersomes and liposomes.

 

This study investigates a novel active system composed of liposomes with encapsulated enzymes. Asymmetry is introduced by incorporating the pore protein alpha-hemolysin, facilitating the diffusion of substrate and products across the vesicle membrane. The resulting asymmetric distribution of species creates a slip velocity on the liposome's surface, resulting in self-propulsion.

 

The nature of the substrate proves to be a critical factor influencing the velocity and direction of the drift of liposomes in a microfluidic channel. Phenomena such as diffusioosmosis and diffusioosmophoresis emerge as inherent components of the motion we measured by tracking polystyrene beads with different surface chemistry in a gradient of urea and glucose. These phenomena are also present in the movement of porated liposomes. In addition to them, a chemotaxis component is observed for the liposomes that have pores. The drift direction and velocity result from all these events and depend on the enzyme/ substrate pair.

 

This research sheds light on some fundamental principles governing liposome chemotaxis with encapsulated enzymes. This system can offer insights into the chemotactic behavior of some natural vesicles and can also be applied in diverse fields, including drug delivery. The interplay between substrate properties, surface interactions, enzyme reactions, and asymmetry opens new horizons for further exploration of chemotaxis in biochemical systems.