Most 3D printing methods currently in use rely on either photo-activated (light)- or thermal (heat) reactions to achieve precise processing of polymers. The development of a new platform technology called direct acoustic printing (DSP), which uses sound waves to produce new objects, may provide a third option.
The process is described in a paper published in Nature Communications. It shows how focused ultrasound can be used to create sonochemical reactions in micro-cavitation regions – basically tiny bubbles. Extreme temperatures and pressures lasting for milliseconds can generate complex, pre-designed geometries that cannot be made with current technologies.
says Muthukumaran Packirisamy, professor and Concordia Research Chair in the Department of Mechanical, Industrial, and Aerospace Engineering at the Gina Cody School of Engineering and Computer Science. He is the author of the corresponding paper.
Mohsen Habibi is a research associate in the Photobiological Microsystems Laboratory at Concordia, and he is the paper’s lead author. His lab colleague, doctoral student Shervin Foroughi, and former master’s student Vahid Karazadeh are co-authors.
As the researchers explain, DSP relies on chemical reactions resulting from pressure fluctuations within 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 highly focused and very objective chemically reactive regions,” Habibie says. “Essentially, bubbles can be used as reactors to trigger chemical reactions to turn liquid resin into solid or semi-solid materials.”
The feedback induced by the ultrasound-guided oscillation within the micro-bubbles is severe, although lasting only a few seconds. The temperature inside the cavity is about 15,000 K and the pressure exceeds 1,000 bar (the Earth’s surface pressure at sea level is about 1 bar). The reaction time is so short that the surrounding material is not affected.
The researchers conducted experiments with a polymer used in the manufacture of additives called polydimethylsiloxane (PDMS). They used a transducer to generate an ultrasonic field that passes through the housing of the building material and solidifies the target liquid resin and deposits it onto a platform or other previously hardened object. The transducer moves along a predetermined path, which ultimately creates the desired product pixel by pixel. The parameters of the microstructure can be manipulated by adjusting the duration of the ultrasound frequency and the viscosity of the material used.
Versatile and specific
The authors believe that the versatility of DSP will benefit industries that rely on highly precise, highly specific equipment. For example, polymer PDMS is widely used in the microfluidics industry, where manufacturers require controlled environments (cleanrooms) and advanced lithographic technology to create medical devices and biosensors.
Space engineering and repair can also benefit from DSP, where ultrasound penetrates opaque surfaces such as metal shells. This could allow maintenance crews to service parts deep within the fuselage that are inaccessible to photoactive feedback printing techniques. DSP even could have medical applications for remote in-body printing for humans and other animals.
“We’ve demonstrated that we can print multiple materials, including polymers and ceramics,” Backersami says. “We’ll be experimenting with metal-polymer composites next, and eventually we want to start printing the metal using this method.”
The study received funding from ALIGO INNOVATION, Concordia and Fonds de Recherche du Québec – Nature et Technologies (FRQNT).
Material provided by Concordia University. Original by Patrick Legetini. Note: Content can be modified according to style and length.