Most currently used 3D printing methods rely on either photo (light) or thermo (heat) activated reactions to achieve accurate polymer handling. The development of a new technology platform 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 ultrasonic waves can be used to create sonochemical reactions in tiny cavitation areas – essentially small bubbles. Extremes of temperature and pressure lasting a trillionth of a second can create pre-designed complex geometries that cannot be created using existing techniques.
“Ultrasound frequencies are already used in destructive processes such as laser ablation of tissues and tumors. We wanted to use them to create something,” says Muthukumaran Packirisamy, Concordia’s professor and head of research at the Department of Mechanical, Industrial and Aeronautical Engineering, Gina Cody School of Engineering and Engineering. Computer Science. He is the corresponding author of the article.
Mohsen Habibi, a researcher at Concordia’s Optical-Bio Microsystems Lab, is the lead author of the article. The co-authors are his laboratory colleague and doctoral student Shervin Foroughi and former master’s student Vahid Karamzadeh.
As the researchers explain, DSP relies on chemical reactions created by pressure fluctuations within small bubbles suspended in a liquid polymer solution.
“We’ve found that if we use a certain type of ultrasound with a certain frequency and power, we can create very local, highly focused chemically reactive regions,” says Habibi. “In principle, bubbles can be used as reactors to control chemical reactions to convert liquid resin to solids or semi-solids.”
Reactions caused by oscillations directed by ultrasonic waves inside microbubbles are intense, even if they last only picoseconds. The temperature inside the cavity shoots up to about 15,000 Kelvin and the pressure exceeds 1,000 bar (the surface pressure of the Earth at sea level is around one bar). The reaction time is so short that the surrounding material is not affected.
The researchers experimented with a polymer used to make additives 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 on a platform or other previously solidified object. The sensor moves along a predetermined path, or produces the desired product pixel by pixel. The microstructure parameters can be adjusted by adjusting the duration of the ultrasonic wave frequency and the viscosity of the material used.
Versatile and specific
The authors believe that the versatility of DSPs will benefit industries that rely on highly specific and delicate devices. For example, PDMS polymer is widely used in the microfluidic industry, where manufacturers require controlled environments (clean rooms) and sophisticated lithographic techniques to create medical devices and biosensors.
Aerospace engineering and repairs can also benefit from DSPs because ultrasonic waves penetrate opaque surfaces such as metal shells. This may allow maintenance crews to service parts located deep in the fuselage that would be inaccessible to printing techniques dependent on photoactivated reactions. The DSP could even have medical applications for remote printing in the body for humans and other animals.
“We have proven that we can print a variety of materials, including polymers and ceramics,” says Packirisamy. “Next time we try polymer-metal composites and eventually we want to get to metal printing using this method.”
The study received funding from ALIGO INNOVATION, Concordia and the Quebec Research and Development Fund – Nature and Technologies (FRQNT).
Materials provided by University of Concordia. Original written by Patrick Lejtenyi. Note: The content can be adjusted in terms of style and length.
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