(379d) Directional Migration of Active and Inactive Liposomes

The objective of this talk is to examine and evaluate the directional migration of active and inactive liposomes. Directional migration of membrane-bound colloids in response to concentration gradients is a crucial characteristic of transport in biological systems. Soft colloids such as liposomes have recently come under the spotlight as potential motors or drug delivery carriers due to their high compatibility with biological systems. When developing such materials, it is important to form confined structures, that are able to move autonomously towards substrates or away from toxins. Recent literature shows that a large number of enzymes as well as particles coated with enzymes are able to move towards higher substrate concentration driven by enzyme propulsion. While this positive chemotactic movement is well observed and studied, the observation of enzyme-mediated negative chemotactic movement is relatively new. In this work, we synthesized enzyme-coated liposomes using enzymes such as catalase and glucose oxidase, and tested their motion in substrate gradients imposed in microfluidic channels. We report that active and inactive liposomes undergo negative chemotaxis under gradients of imposed substrate. Active liposomes show directional movement based on the interplay of substrate turnover, self-generated solute gradients and/or biologically relevant external ionic gradients. Our results indicate that none of the currently known mechanisms explain the speeds observed in experiments, opening possibilities for new models of chemically driven transport.