Microfluidics Research Could Benefit Drug-Delivery Devices

Focusing surface vibrations onto a water droplet causes it erupt into a narrow jet. The technique could be used in biomedical research or drug-delivery applications.

Fluid jets are normally formed by forcing a liquid through a small opening—as is exemplified in the case of a syringe. But Australian researchers have found another way, using focused surface acoustic waves (SAWs) to form a fluid jet from an isolated droplet, writes Marcus Woo in Physical Review Letters. The research team, led by Leslie Yeo of Monash University, the researchers believe the technique could be useful in drug delivery, biomedical research and inkjet printing.

The acoustic waves, which are nano-sized versions of the seismic surface waves caused by earthquakes, were formed using two electrodes on a lithium-niobate piezoelectric surface. The electrodes, made from arrays of curved metal strips, or arcs, took up two 90-degree sectors of a disk shape, with a hole in the center. The arrays focused SAWs from opposite directions into the center, where the researchers placed a 1- to 5-microliter drop of water, ethanol, methanol or octanol.
The vibrations, at a frequency of 30 MHz, triggered different behaviors in the droplets, depending on the vertical acceleration of the waves, which the team controlled with slight changes in their amplitude. For smaller amplitudes, the force wasn’t strong enough to overcome the droplet’s surface tension, so it merely oscillated in place, sloshing between a flattened and peaked shape. For large-amplitude SAWs, the mountain erupted into a jet 1 to 2 cm high, reaching speeds of several meters per second. Especially high amplitudes, broke the jet up into a series of small droplets. The largest SAWs caused the droplet to atomise into tiny droplets.

Resarchers at Monash University used acoustic waves to form fluid jets.

In microfluidics, propelling liquid through micron-scale channels can require considerable effort as a result of the force required to overcome high surface tension. Many microfluidic devices, which are often as small as a credit card, must be attached to a comparatively large pump, resulting in an unwieldy and inefficient arrangement. Using SAWs to transport fluids could be a more-efficient arrangement.

The next step, Yeo says, is to develop more precise ways to control the jets for future applications. For example, small devices could employ jets to efficiently deliver accurate doses of drugs. The miniaturisation made possible by SAW-induced jets could also result in smaller and more efficient DNA microarrays, which are used to analyse thousands of genes at once in the study of diseases. Another application is inkjet printers, which now rely on nozzles to shoot tiny drops of ink onto paper.

More information is available from Physical Review Letters.

Tags: biomedical research, Drug delivery, Marcus Woo, microfluidics, Monash University, Physical Review Letters