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===Biomimetic self-assembly of helical electrical circuits using orthogonal capillary interactions===

David H. Garcia, Mila Boncheve, Osahon Omoregie, and George M. Whitesides

Applied Physics Letters. Volume 80, Number 15 (15 April 2002)

'''Keywords:''' [[capillary]], [[biomimetic]], [[self-assembly]]

==Summary==
 
The authors are inspired by the self-assembly of the Tobacco Mosaic Virus to create a new method for making mesoscale electric circuits. The virus consists of a single strand of RNA surround by a helical protein coat. To produce more complex structures than previously created in the  lab, the researchers used a two-step process: (1) '''nucleation''' of disk-shaped assemblies of wedges and (2) '''elongation''' of these nuclei into helices. The specific system that the authors used was a collection of wedge-shaped pieces of polyurethane ('''(a)''') coated with patches of solder and hydrophobic regions ('''(d)-(f)'''). The first and last wedge overlapped slightly, since the chiral faces were separated by 66 degrees (see '''(b)''' and '''(c)'''. These pieces assembled themselves into helices ('''(g)''' and '''(h)''') while being tumbled for about an hour in a rotary evaporator than contained a hydrophobic lubricant.

[[Image:GarciasFig01.jpg | 300 px]]

==Soft matter aspects==

Two types of capillary interactions allow the assembly of the helices: (1) between patterns of '''solder''' are imprinted narrow, chiral edges of each wedge and (2) between '''hydrophobic''' surfaces on the large, flat top and bottom surfaces. Capillary forces caused the chiral edges of the wedges to bind together, forming disks of at least six wedges. However, the capillary forces caused by the hydrophobic surfaces was needed to extend the helix past about 14 wedges. To show the versatility of this technique and suggest a possible application, the researchers created a helix with two separate electrical wires along the edge of the helix, using the pattern of copper and solder shown in '''(a)-(c)'''. Photographs of the resulting helices are shown in '''(d)''' and '''(e)'''. They verified the electrical continuity over a full-scale helix to demonstrate the versatility of the technique (see '''(f)''' and '''(g)''' for a schematic).

[[Image:GarciasFig02.jpg | 300 px]]

''written by: Naveen Sinha''