Sheath flow device and method

A method of creating a sheathed flow comprising:

• providing a channel having a proximal end and a distal end, said channel having opposed facing top and bottom surfaces, said channel having at least one first fluid transporting structure across said channel located on said top surface and at least one second fluid transporting structure across said channel located on said bottom surface, said first and second fluid transporting structures being located between said proximal and said distal end and on said opposing faces surfaces, facing one another across the channel;
• and
• introducing a sheath stream and a core stream at said proximal end of said channel, said sheath and core streams flowing down said channel side by side towards said distal end, wherein said fluid transporting structures transport said sheath stream across said top and bottom surfaces of said channel to surround said core stream, thereby creating a sheathed flow.