Guest editorial article: special issue on micro- and nanoscale flows: advancing the engineering science and design

In the early 1980s the UK was at the forefront of developing microsystems technologies. Pioneering work was carried out on ink-jets at Cambridge, and pregnancy self-testing kits were developed by Unilever. Both of these were early applications of the subject that is now known as microfluidics. However, despite these early successes, recent progress in the field has not been so obvious. Internationally, there have been substantial investments into micro and nano-technology but for many years the UK failed to build on its early successes. In 2003 this changed, and the UK recognized the vital role that micro- and nano-technology will play in all scientific areas by beginning an internationally competitive research programme. Research into microfluidic technologies has clearly benefited from international investment. For example, ink-jet technologies are being used for applications including rapid prototyping, nano-electronics, flexible displays, micro- and nano-fluidics, bio-arrays, etc. Microfluidics is also being used in a wide range of other applications, including drug discovery, lab-on-a-chip, speciality chemicals, drug delivery, personal healthcare, micro-reactors, and sensors. However, although major progress has been made, particularly in fabricating novel devices, the theory and science underpinning these innovations, and particularly their rational design, has clearly not kept pace.