Turning Bubbles into Microscopic Syringes

Turning bubbles into microscopic syringes through the use of sound has been experimentally shown by researchers in the Netherlands (Claus-Dieter Ohl, University of Twente, 011-31-53-489-5604), demonstrating a potential method for injecting drugs and genes into specific regions of a patient's body. Taking high-speed microscopic photographs, the researchers revealed that even bubbles much smaller than the thickness of a human hair could transform into a needle-like tube, delivering a billionth of a millionth of a gallon of liquid. While this sub-nanofluidic volume seems very small, it is more than enough to transfer large molecules (such as DNA and most drugs) into desired cells for medical therapy.

In their experiment, the researchers start with a room-temperature container of water that was slightly "degassed," or had some oxygen gas removed from it. Inside the water container, they create tiny bubbles between 7 and 55 microns in size. Next, they broadcast high-intensity ultrasound into the liquid, creating supersonic disturbances known as shock waves. Slamming against the microscopic bubbles and squeezing them into needle-like shapes, the shock waves also introduce small amounts of surrounding liquid into the bubble. The liquid shoots through the bubble at very high speed, punctures its opposite end, and continues outside as a high-speed stream of fluid resembling a syringe. Based on the speed of the flow, the researchers expect that this liquid stream could easily penetrate a nearby cell membrane. Dissolved drugs or genetic material surrounding specially designed microbubbles could therefore be injected into targeted cells. Long suspected but now confirmed, the acoustically driven metamorphosis of bubbles into micro-syringes could someday become a useful medical tool. (Ohl and Ikink, Physical Review Letters, 30 May 2003).

While this work aims to inject material deeply into living cells, other U-Twente researchers have just introduced a new acoustic method for manipulating cells: they devised a "sonoporation" technique which uses gently oscillating bubbles attached to a surface to deform or even puncture cell membranes (Marmottant and Hilgenfeldt, Nature, 8 May 2003).