Researchers at 3-D printing R&D powerhouse Nanyang Technological University in Singapore have used cutting-edge technology to enhance the precision and power of ultrasound devices.

The team has developed a novel way to develop transducers, capable of controlling “high-pressure ultrasound to move, manipulate, or destroy tiny objects like particles, drops or biological tissue at scales comparable with cells,” according to the American Institute of Physics report of a paper recently published in its Applied Physics Letters.

This could result in greater precision in surgery at the smallest scale.

"The advantage of acoustics is that it's noninvasive," senior author Claus-Dieter Ohl at Nanyang Technological University in Singapore told the AIP, noting that the new device gave them “much better control of the photo-acoustic wave, and the wave can be even designed such that it serves the purpose of a mechanical actuator."

The breakthrough allows for control beyond what was previously possible. Before this latest development only basic acoustic planar waves could be manipulated. This permitted only the ability to focus on a single point, like “a magnifying glass focuses light waves,” according to the report.

Standard laser-generated focused ultrasound transducers (LGFU) using a substrate of glass coating with nanotubes can only form basic shapes because it is hard to make complex structures from glass. When the nanotubes are heated they convert that heat to high-pressure acoustic waves, but the basic shapes of the materials yield acoustic waves of similarly basic shapes, according to the report.

According to researchers Chan, Thomas Hies and Ohl the physics challenge is that, “to generate more complex wave fronts than a single focused or planar wave, surfaces with a nontrivial shape are needed." However, the substrates of the present photo-acoustic transducers are glass lenses, which limit the geometry to that offered from the lens manufacturer, e.g., planar, cylindrical, or spherical.

Their new approach could overcome this challenge by “using arbitrarily shaped yet smooth surfaces,” they point out, that “would allow emitting photo-acoustic waves with a controlled phase resembling [a] hologram."

To achieve such shapes they used 3-D printing, noting that it held the promise “to construct polymer-based surfaces with high accuracy at low cost."

The requirements of the replacement substrate are that they “need to be sufficiently transparent to light, smooth, and offer good acoustic properties. Additionally, we need to develop a deposition technique compatible with the low melting temperature of the transducer substrates.

The latest effort does just that. It replaces the glass with liquid resin, which let researchers make any shape no matter how complex – which in turn can generate complex acoustic waves of any form as well.

“We demonstrate three 3-D printing techniques for LGFU transducers, and one of them reveals similar, if not a better, performance than a glass substrate,” lead author Weiwei Chan noted in the journal article.

This permits much more precise and complicated manipulations of matter in tasks such as surgery, at a minute level, with greater precision.

A number of problems needed to be overcome to create the new transducer, and a new approach to coating the substrate had to be developed so that polymer and nanotubes could be deposited on the substrate at room temperature, so as not to deform or melt the resin.

The usual way to coat the substrate involves depositing material at high temperature.

In addition to increasing the control of the waves, the method was also relatively cheap – about two dollars each to print.

"It allows you to use acoustics for new applications," Ohl told AIP.

This is because this new transducer approach boosts the accuracy of focus – to hundreds of microns – and that permits heretofore unattainable precision, he stressed, noting that it could make this viable for such delicate procedures as eye surgery.