Digital sound printing in 3D with ultrasound

Digital sound printing in 3D with ultrasound

Technology News |
By Nick Flaherty

Researchers in Canada have developed a technique that uses ultrasonic soundwaves for digital 3D printing of materials.

Most 3D printing methods currently in use rely either on light or heat to achieve reasonably precise manipulation of polymers. Direct sound printing (DSP), developed at Concordia University in Canada, offers a third option that can even be used to create medical devices in situ.

The ultrasound waves are used to create sonochemical reactions in minuscule cavitation regions, tiny bubbles suspended in a liquid polymer solution.

“Ultrasonic frequencies are already being used in destructive procedures like laser ablation of tissues and tumours. We wanted to use them to create something,” said Muthukumaran Packirisamy, a professor and Concordia Research Chair in the Department of Mechanical, Industrial and Aerospace Engineering at the Gina Cody School of Engineering and Computer Science.

“We found that if we use a certain type of ultrasound with a certain frequency and power, we can create very local, very focused chemically reactive regions,” said Mohsen Habibi, a research associate at Concordia’s Optical-Bio Microsystems Lab and the paper’s lead author. His lab colleague and PhD student Shervin Foroughi and former master’s student Vahid Karamzadeh are co-authors.

“Basically, the bubbles can be used as reactors to drive chemical reactions to transform liquid resin into solids or semi-solids,” he said.  

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The temperature inside the cavity can rise as high as 15,000 Kelvin and pressure exceeds 1,000 but the at picoseconds, the reaction time is so brief the surrounding material is not affected. The process is described in a paper published in Nature Communications

The researchers experimented on a polymer used in additive manufacturing called polydimethylsiloxane (PDMS). They used a transducer to generate an ultrasonic field that passes through the build material’s shell and solidifies the targeted liquid resin and deposits it onto a platform or another previously solidified object. The transducer moves along a predetermined path, eventually creating the desired product pixel by pixel. The microstructure’s parameters can be manipulated by adjusting the duration of the ultrasound wave’s frequency and the viscosity of the material being used.

The XY printing resolution in DSP depends on the input parameters of the process of which ultrasound frequency plays a key role, higher the frequency smaller the feature size. A 2.15 MHz ultrasound frequency with PDMS with a mixing ratio of 17:1 leads to 450 μm lines with 500 μm empty gaps. A 2.4 MHz ultrasound frequency leads to smaller line width of 380 μm and a gap width of 75 μm

Printing with the 2.4 MHz in PDMS with a mixing ratio of 10:1 with porous structures leads to 280 μm line and a 630 μm gap. This can be reduced 186 μm with a 280 μm gap. 

The geometry of the spherically focused transducer also affects the printing resolution since the focal size depends on it. The focal spot size considering −6 dB drop off points depends on geometrical parameters such as the radius of the curvature of the transducer surface and the active radius.

The PDMS polymer is widely used in the microfluidics industry, where manufacturers require cleanrooms and sophisticated lithographic technique to create medical devices and biosensors.

Aerospace engineering and repair can also benefit from DSP, as ultrasound waves penetrate opaque surfaces like metallic shells. This can allow maintenance crews to service parts located deep within an aircraft’s fuselage that would be inaccessible to printing techniques reliant on photoactivated reactions. DSP could even have medical applications for remote in-body printing for humans and other animals.

“We proved that we can print multiple materials, including polymers and ceramics,” Packirisamy says. “We are going to try polymer-metal composites next, and eventually we want to get to printing metal using this method.”



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