Most 3D printing methods currently in use rely on activated photo (light) or thermo (heat) reactions to achieve precise manipulation of polymers. The development of a new platform technology called direct sound printing (DSP), which uses sound waves to produce new objects, may offer a third option.
The process is described in an article published in Nature Communication. It shows how focused ultrasound waves can be used to create sonochemical reactions in tiny regions of cavitation – essentially tiny bubbles. Extreme temperatures and pressures that last for trillionths of a second can generate complex pre-engineered geometries that cannot be achieved with existing techniques.
“Ultrasound frequencies are already used in destructive procedures like laser ablation of tissue and tumors. We wanted to use them to create something,” says Muthukumaran Packirisamy, professor and Concordia Research Chair in the Department of Mechanical, Industrial and Aerospace Engineering at Gina Cody University School of Engineering and Computer Science. He is the corresponding author of the journal.
Mohsen Habibi, a research associate at Concordia’s Optical-Bio Microsystems Laboratory, is the lead author of the paper. His lab colleague and doctoral student Shervin Foroughi and former master’s student Vahid Karamzadeh are co-authors.
As the researchers explain, DSP relies on chemical reactions created by fluctuating pressure inside tiny bubbles suspended in a liquid polymer solution.
“We found that if we use a certain type of ultrasound with a certain frequency and power, we can create very local and very targeted chemically reactive regions,” says Habibi. “Basically, bubbles can be used as reactors to drive chemical reactions to turn liquid resin into solids or semi-solids.”
The reactions caused by the directed oscillation of the ultrasonic waves inside the microbubbles are intense, although they only last for picoseconds. The temperature inside the cavity climbs to about 15,000 Kelvin and the pressure exceeds 1,000 bar (the pressure on the Earth’s surface at sea level is about one bar). The reaction time is so short that the surrounding material is not affected.
The researchers experimented with a polymer used in additive manufacturing called polydimethylsiloxane (PDMS). They used a transducer to generate an ultrasonic field that passes through the shell of the building material and solidifies the targeted liquid resin and deposits it onto a platform or other previously solidified object. The transducer moves along a predetermined path, eventually creating the desired product pixel by pixel. The parameters of the microstructure can be manipulated by adjusting the duration of the ultrasound wave frequency and the viscosity of the material used.
Versatile and specific
The authors believe that the versatility of DSP will benefit industries that depend on very specific and delicate equipment. PDMS polymer, for example, is widely used in the microfluidic industry, where manufacturers need controlled environments (clean rooms) and sophisticated lithography technique to create medical devices and biosensors.
Aerospace engineering and repair can also benefit from DSP because ultrasonic waves penetrate opaque surfaces like metal hulls. This can allow maintenance crews to service parts located deep within an aircraft’s fuselage that would be inaccessible to printing techniques based on photoactivated reactions. DSP could even have medical applications for remote body imprinting for humans and other animals.
“We have proven that we can print multiple materials, including polymers and ceramics,” Packirisamy says. “We will then try polymer-metal composites, and eventually we want to get to printing metal using this method.”
The study was funded by ALIGO INNOVATION, Concordia and the Fonds de recherche du Québec — Nature et technologies (FRQNT).
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Material provided by Concordia University. Original written by Patrick Lejtenyi. Note: Content may be edited for style and length.