Tiny object manipulation gets assist from ultrasound and 3D-printed lens

Nanyang Technological University's proof-of-concept model of the transducer lens(Credit: Weiwei Chan)

Do you know what a laser-generated focused ultrasound transducer is? Basically, it's a device that converts laser light into focused acoustic waves, which can in turn be used to move cell-sized tiny objects. It's a fascinating technology, and it's recently been improved upon. Led by Prof. Claus-Dieter Ohl, a team at Singapore's Nanyang Technological University has created a 3D-printed lens that allows the transducers to operate with even more precision.

In a traditional setup, pulses of laser light hit a glass lens that is coated with a thin film of carbon nanotubes. The heat from the laser causes that coating to rapidly expand, creating vibrations that become the acoustic waves.

The glass lenses can only be formed in a limited number of shapes, however, which means that they can only focus each acoustic wave down to a single point – it's not unlike using a magnifying glass to focus sunlight. That's where the new lens comes in.

Because it's 3D-printed from a clear resin, it can be made in any shape desired. Among other things, this means that it can focus the waves at multiple points simultaneously, or it can sequentially focus them at different points at different times.

As an added bonus, the polymer is cheaper than glass – the team's two-square-centimeter proof-of-concept model cost about two US dollars to print.

Possible applications for the technology include microsurgery, materials analysis, and the fine manipulation of liquids in microfluidic devices.

A paper on the research was recently published in the journal Applied Physics Letters.

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