Technologists have 3D-printed a new kind of device that can utilise high-pressure ultrasound to move, manipulate or destroy objects at cell-level sizes
These 3D printed devices provide unprecedented control of photoacoustic waves, which are generated by lasers. They can be used to manipulate or destroy particles, drops or biological tissue, making for applications in precise surgery, analysing the properties of materials, and for scientific research in the lab, such as in the field of microfluidics.
Ultrasound, or high-frequency acoustic waves, can be used not just for pre-natal imaging, but also to destroy cancer cells. Ultrasound can be fired into materials to test their properties.
According to Claus-Dieter Ohl at the Nanyang Technological University in Singapore, the advantage of acoustics is that it is non-invasive.
"We have much better control of the photoacoustic wave, and the wave can be even designed such that it serves the purpose of a mechanical actuator," he explained. "It allows you to use acoustics for new applications.
Currently, laser-generated focused ultrasound transducers work by converting laser pulses into vibrations. Within the transducer, a glass surface, coated with a thin film of carbon nanotubes, acts like a lens. The laser pulses hit the glass surface, causing the nanotube coating to expand rapidly, generating the vibrations needed to produce high-frequency and high-pressure acoustic waves.
However, because the substrate material is glass, it is limited to planar, cylindrical or spherical shapes, because more complicated shapes are difficult and expensive to make out of glass.
This meant that these ultrasound transducers can only produce basic types of acoustic waves: planar waves, which focus to a single point, much like how a magnifying glass focuses light waves.
By creating more complicated lenses for their transducer, the researchers are able to generate acoustic waves of any shape. They are able to focus the waves at multiple points at the same time, or they can control the phase of the waves, focusing them on different points at various times, on demand.
The team created their transducer lens by using 3D printers to create the lens out of clear liquid resin. They developed a new method to coat the clear resin by by painting layers of polymer and carbon nanotubes at room temperature.
While the team did consider conventional coating methods like vapour deposition, the high temperatures required by such processes would have melted the cured resin.
In their tests, the scientists found their proof-of-concept transducer generates a planar and focused wave at the same time, and it performed as well as a glass one. About two square centimeters in size, it costs only about two dollars to print.
Because this approach is not just cost-effective, but also offers highly precise focus (down to hundreds of microns), it opens up applications in material analysis and surgery. This device could help doctors better attack tumors. Eye surgeons could use the focused ultrasound waves to conduct precise cataract surgery, while biomedical researchers can use acoustic waves to measure the elastic properties of cells in a petri dish, seeing how they respond to forces.
The ability to focus waves at different points and times allows the device to exert shear forces, in order to sort, isolate and manipulate, even destroy droplets, particles, or biological cells. It could be used to improve control over liquids in microfluidic applications, and also used to make actuators.