• Dr. Valery Luchnikov
• Kamlesh Kumar

We fabricate polymer and composite polymer/metal tubes of mesoscopic dimensions by self-rolling of thin bilayer polymer films which are released in controllable manner from a solid substrate.¹ The bending moment arise due to different swelling of the components of the bilayer in a selective solvent. As a model system we explore polystyrene/poly(4-vinylpyridine) (PS/P4VP) bilayer which rolls in acidic water due to selective swelling of P4VP.

The major advantage of the approach is the possibility to functionalize the inner surface of the tubes by variety of planar methods, such as micro-contact printing, photolithography, plasma treatment, prior to the tube formation by film rolling. This opens new opportunities for the engineering of micro- and nanodevices based on tubular elements such as sensors, micro-reactors, chromatographic capillaries etc. For example geometrically complex patterns (i.e. arrays of hydrophobic/hydrophilic spots, stripes or spirals of definite handedness) can be easily created inside microchannels by micro-contact printing on the bilayer prior to rolling. On the other hand, the properties of the confining walls have the utmost importance for the physico-chemical processes in the micro- and nanocontainers.

Micro-syringes and microfluidic circuits fabricated with use of self-rolled tubes with functionalized inner surface can find applications in bio-medical research and drug-delivery systems.

fig. 1 Fabrication of the self polymer tubes with functinalized inner surface. A) Creation of the polymer bilayer on a solid substrate by dip -or spin-coating. B) Functionalization of the top layer (i.e. by micro-contact printing.) C) Presetting of the rolling direction by lithographic windows. D) Rolling of the bilayer in a solvent due to selective swelling of the bottom component and/or the selective etch of the sacrificial layer.	fig. 2 A) AFM topography image of a sub-micron tube. The inset: height profile along the straight line segment. The total length of the tube is at least 40mm B) Optical micrograph of a bunch of polymer tubes with the topographically and chemically structured inner surface. The tubes are approximately 2cm-long and their length is restricted only by the dimensions of the substrate (the silicon wafer). The topography features on the inner surface of the tubes were created by the local melt of polystyrene under the pins of PDMS stamp swollen in toluhene. The optical contrast of the topography features was enhanced by magnetron sputtering of gold.