Transport Modes in Nanotube-Vesicle Networks

Doktorsavhandling, 2006

Methods for construction of surface-immobilized microscopic networks of phospholipid bilayer vesicles (3-50 µm in diameter) interconnected by lipid tubes (30-150 nm in radius), have previously been developed. The networks have controlled connectivity and are well-defined with regard to container size, content, angle between nanotube extensions, and nanotube length. Within networks, the nanotubes spontaneously arrange themselves into three-way junctions with an angle of 120˚ between each nanotube, by minimizing the tube length. Using a combination of electroinjection, electrofusion, spontaneous nanotube rearrangement and satellite-vesicle injection, complex networks of containers and nanotubes can be created. In this work three transport modes have been successfully developed and employed in the nanotube-vesicle networks; Marangoni transport, caused by membrane tension gradients, electrophoretic transport, caused by electric field gradients, and diffusive transport, caused by concentration gradients. The transport mechanisms are described and compared with regard to membrane, fluid and analyte movement. Marangoni and electrophoretic transport are active modes, and require micromanipulation to introduce force fields. Both active methods feature controlled and variable transport velocities ranging from 1 to 100 µm/s. Diffusive transport is a passive mode, and once a concentration gradient is created there is no further need for micromanipulations. These three methods have been used for controlled transport of latex particles and DNA molecules of various sizes, as well as proteins and small fluorophores. The three transport modes complement each other with regard to bulk as well as single-molecule transport. Combined with sensitive detection schemes the transport modes make the use of nanotube-vesicle networks as biomimetic devices viable for simulating and replicating cellular transport and reaction processes. Examples presented in this thesis include studies of DNA conformation in confined geometries and the propagation of an enzymatic reaction in structured geometries.