Scientists of the University of Twente (The Netherlands) succeed in speeding up the fluid flow in a micro channel using tiny and rapidly imploding gas bubbles that also provide a new way of mixing fluids within a lab-on-a-chip, without the need of complicated external components. The scientists led by Dr. Claus-Dieter Ohl of the MESA+ Institute for Nanotechnology present their results in a coming June 2007 edition of Physical Review Letters.

Controlled cavitation” is the basis for the new technique: using a laser, a bubble is induced in the micro channel, by local heating and low pressure. This bubble has a short life: it rapidly implodes caused by the higher pressure in the channel. This causes the fluid flow to go up to 20 meters per second. In addition, a jet is formed near a channel wall together with tiny bubbles around which creates a vortex – an ideal way of mixing fluids.

Impoding Bubbles The bubble expands and collapses in a complex geometry. Here, two feeding capillaries connect with a round (left) and rectangular shaped (right) container. A jet flow is created which accelerates the flow towards the left. The movie is taken at 1 million frames per second, and the image width is 140 microns

From project website

In microfluidics, other physical laws become dominant over those valid for large-scale systems. Viscous forces take over, and this implies that often additional components ??for example micromechanical devices- are necessary for mixing and speeding up the flow. Those components , in turn, require additional electronics and wiring and can make a lab-on-a-chip fairly complicated. The laser can be directed to any spot where mixing or acceleration is needed, this is even made easier by the fact that microfluidic systems are often transparent. The MESA+ scientists therefore see their new approach as a powerful new tool in microfluidics and lab-on-a-chip systems.

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