Direct Sound Printing, A Novel 3D Printing Method

Mohsen Habibi, Shervin Foroughi, Vahid Karamzadeh and Muthukumaran Packirisamy of the Optical Bio Microsystems Laboratory, Micro-Nano-Bio Integration Center, Department of Mechanical, Industrial and Aerospace Engineering, Concordia University in Canada, have developed a novel 3D printing technology called Direct Sound Printing (DSP). Although we have Fabrisonic’s Ultrasonic Additive Manufacturing that welds together sheets of metal and the Mimix bioprinter, which uses sound to organise cells into tissue, and others have worked on technologies to print in ultrasonic baths, this process is new.

Direct Sound Printing (DSP) process schematic. Image courtesy of Habibi, M., Foroughi, S., Karamzadeh, V. et al. Direct sound printing/Nature Communications.

With Direct Sound Printing, the team discloses in Nature Communications that:

The “build chamber filled with the build material (monomer mixed with curing agent or different mixtures) through exposing to the focused ultrasonic field. We call this method Direct Sound Printing (DSP). The ultrasonic field, which is generated by a monolithic spherical focused transducer, reaches the build material after passing through the shell of the build chamber. At the focal location in the build material, as shown in Fig. 1a and detailed in Fig. 1b, the chemically active acoustic cavitation region solidifies the liquid resin or mixture and deposits it to the platform, or on top of previously deposited and solidified regions. We call this region as ultra-active micro reactor (UAMR) where generated bubbles and polymerized resin appear at the low-pressure zones and then they migrate momentarily to high-pressure zones until they reach to the platform or previous solidified pixel where they are deposited. The transducer is moved in the medium by a motion manipulator to locate the focal region along a calculated path in the build chamber to create the desired part pixel by pixel. Input parameters of DSP process affect the microstructure of the printed parts. These parameters are characteristics of the transducer driving pulse (such as electrical power, frequency and duty cycle which is the active fraction of the driving pulse period), build materials (such as the mixing ratio of monomer to curing agent, mixture ratio, viscosity and surface tension) and the transducer motion (such as velocity and acceleration of the transducer). Different micro structures result in optically transparent to opaque parts in DSP. The resultant opacity is due to the porous structure of the printed part, which can be controlled/by manipulating the DSP input parameters.”

So the DSP process uses the density of the build material and a change in acoustic pressure to create material inside bubbles that move towards the build platform where they are organised and built. This lets them print with new chemistries. The researchers demonstrated using Sylgard-184, a silicone elastomer, for example, using Polydimethylsiloxane (PDMS) as a curing agent. This material and other heat curing polymers could now be printed because the reactions are so precise, fast, and localised.

The researchers also made a PDMS sponge material and made PDMS molds that were then used to hold microfluidics. They initially are also very optimistic about the biocompatibility of the parts since DSP doesn’t use some of the toxic chemicals or light used by other processes. Besides microfluidics, composites, and polymers, they consider that their approach may be valuable for transparent materials, lab on a chip, organ on a chip, and energy harvesting.

A very exciting variant is Remote Distance Printing (RDP), where you can let the acoustic waves pass through a wall or skin, let’s say, to build an object on the other side of that wall without touching it. The team feels this could be used for “emote repairing or on-site maintenance of hidden parts in aerospace industries and in-vivo remote and noninvasive bioprinting of inside body parts in medical applications.”

They further go on to test printing as “noninvasive deep inside body printing.” Demonstrating that it could be possible, for example, to harden and build a structure inside the human body while the 3D printer was outside of it. This could potentially be a completely new approach whereby, for example, you could inject a material and then locally print it into a defined structure without surgery. You could get a facelift without getting cut open or do a transaction in a patient using an injected material that is then 3D printed in place, turning it from a liquid into a staple.

It remains to be seen if these applications will work at scale and find commercial venues. But, new technology is always very exciting and gives us new perspectives. Mohsen Habibi and Muthukumaran Packirisamy have filed a patent application and obtained a patent which means that this technology has been a long time coming and points to them seeking commercialisation in some way.

In their patents, they talk about two methods where “Selective Spatial Solidification forms the piece-part directly within the selected build material whilst Selective Spatial Trapping injects the build material into the chamber and selectively directs it to accretion points in a continuous manner.” This may point to them having an eminently controllable process that could in a layer less way produce controlled porosity or could selectively sinter powder in a new way.