Project B4: Active microfluidics based on self-propelling molecular machines.

Theoretical investigations of thin liquid films with floating molecular machines,
viewed as active surfactants, are planned. In addition to capillary surface forces,
floating machines generate propulsion forces applied as additional pressure to
the liquid-air interface. Similar to biomembranes with active inclusions, flat inter-
faces may become unstable. This can lead to spontaneous formation of traveling
machine clusters, of hydrodynamical flows in the liquid film and interface turbulence.
The possibility of using floating machines to induce and control microfluidic flows will
be explored. For this purpose, we can use the fact that active operation of protein
machines can be externally regulated by light or by chemical inhibitors. Controlled
spatial gradients of machine activity can thus be created, inducing hydrodynamical
flows or guiding spontaneous pattern formation in microfluidic systems.
Investigations will be performed both for low surface densities of floating machines,
where individual machines are independent, and for the situation where this density
is high leading to interactions between floating proteins. In the latter case, phase
transitions and formation of traveling dense protein rafts in the active molecular bio-
layer should be considered.
Hydrodynamical models of thin films in the lubrication approximation will be used.
Hydrodynamical equations will be complemented by the dynamical equation describing
spatial redistribution of floating machines over the surface, caused by hydrodynamical
flows in the film and molecular diffusion processes. Analytical stability investigations
will be performed and extensive numerical simulations of such systems will be undertaken.


Project leaders: Prof.Dr.  A. Mikhailov [1],  Prof.Dr.  H. Engel [2],  Prof. Dr.  C. Beta [3]