I used to think acoustics was just about what type of room was best for a musical ensemble to play in, as that was a regular concern of mine when I was actively playing musical instruments on an almost daily basis from the ages of about 13-22. I wasn’t entirely wrong, though a bit pedestrian in my thinking: acoustics is a branch of physics focused on the study of mechanical waves in gases, liquids, and solids, including topics like infrasound, ultrasound, sound, and vibration. So, that’s anything to do with sound waves, whether we’re manipulating them to make better 3D prints, separating simultaneous overlapping sounds from different sources, or cloaking and tagging items.
A collaborative team of researchers from the University of Bath and the University of Bristol in the UK have been studying how to use sound to manipulate particles for a next-generation 3D printing method that’s faster and more precise. The team is using computer-controlled ultrasound to fabricate pre-determined patterns out of aerosol droplets or particles on surface substrates in a process known as sonolithography. This process could result in great benefits for various applications like printed electronics, industrial painting and spray coating, and even biofabrication.
“The interference of the waves generates an acoustic field with defined regions of high and low pressure. Droplets or particles moving through this field migrate to specific regions based upon this pressure distribution and the properties of the materials (e.g. size, density),” Dr. Jenna Shapiro, research associate in the School of Cellular and Molecular Medicine at the University of Bristol, explained in an interview with Design News.
The researchers, who were inspired by the maker movement and advances in particle manipulation and ultrasonic levitation, worked together to develop, as Dr. Shapiro explained, “accessible fabrication tools using ultrasonic standing waves.” They published their results in a paper titled “Sonolithography: In-Air Ultrasonic Particulate and Droplet Manipulation for Multiscale Surface Patterning.”
The abstract reads, “Sonolithography is based on the application of acoustic radiation forces arising from the interference of ultrasonic standing waves to direct airborne particle/droplet accumulation in defined spatial regions. This approach enables reliable and repeatable patterning of materials onto a substrate to provide spatially localized topographical or biochemical cues, structural features, or other functionalities that are relevant to biofabrication and tissue engineering applications. The technique capitalizes on inexpensive, commercially available transducers and electronics. Sonolithography is capable of rapidly patterning micrometer to millimeter scale materials onto a wide variety of substrates over a macroscale (cm2) surface area and can be used for both indirect and direct cell patterning.”
Sonolithography uses arrays of acoustic standing waves in the air, which have been generated from ultrasonic speakers. Then, the materials are deposited, in the acoustic field-determined pattern, onto a substrate.
“It’s essentially as if the field is acting as a stencil or a mask, driving the materials into specific areas,” Dr. Shapiro explained.
Dr. Shapiro says that their sonolithography method can “print” patterned surfaces up to 20 square centimers in less than 30 seconds.
“The power of ultrasound has already been shown to levitate small particles. We are excited to have hugely expanded the range of applications by patterning dense clouds of material in air at scale and being able to algorithmically control how the material settles into shapes,” said Professor Mike Fraser from the Department of Computer Science at the University of Bath.
The team’s process allows for plenty of flexibility in the deposited materials, like proteins, mammalian cells, and aerosols, as well as in the substrate. Sonolithography is said to be most effective when the same pattern has to be repeatedly applied to multiple surfaces. Additionally, the method is modular, so any of the steps, like the patterning array or method of droplet generation, can be improved upon, or even just switched out.
Dr. Shapiro explained, “This means there is still plenty of room for innovation and improvement. In the fabrication space, we have shown that the material selection can be largely decoupled from the patterning itself, opening this up to a range of potential applications.”
The next step is to work on real-time manipulation of the acoustic field and subsequent patterning by adding dynamic control into the process.
“The objects we are manipulating are the size of water drops in clouds. It’s incredibly exciting to be able to move such small things with such fine control,” explained Professor Bruce Drinkwater, professor of Ultrasonics in Bristol University’s Department of Mechanical Engineering. “This could allow us to direct aerosol sprays with unheard of precision, with applications such as drug delivery or wound healing.”
Dr. Shapiro has a background in tissue engineering and biomaterials, so was most interested in sonolithography’s potential for biomedicine.
“Sonolithography enables gentle, non-contact and rapid patterning of cells and biomaterials on surfaces,” she explained. “Tissue engineering can use biofabrication methods to build defined structures of cells and materials. We are adding a new technique to the biofabrication toolbox.
“I am currently studying how sonolithography can be used to generate unique biomaterial microarchitectures and how these in turn impact cell-material relationships. I want to explore how this technique can be further developed, or used in combination with existing tools, toward creation of mammalian tissues for modeling and regenerative medicine.”
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