A group of researchers from Harvard University has done the unthinkable. They have found a way to print objects using sound. This process is called “acoustophoretic printing” and according to a press release, “this method could enable the manufacture of many new biopharmaceuticals, cosmetics, food, and expand the possibilities of optical and conductive materials.” 3D printing, in general, is a worldwide industry and continues to grow day after day. It already encompasses different forms of technology and materials. 3D printing has been divided into metal, fabrics, bio, and many other industries. It has become an important part of our society because of the inkjet printing process and thanks to this research, it has made an even bigger jump forward.
The Process Of 3D Printing And Viscosity
The entire process of basic 3D printing begins with a model on your computer. That digital design is usually a Computer Aided Design (CAD) file and the final model is created either from data generated with a 3D scanner or from the ground up 3D modeling software which is the most common method. 3D printing has started to become more popular especially in education. It enables students to materialize their ideas in a fast and somewhat affordable way. Inkjet 3D printing utilizes fluid liquid droplets of microliter-to-nanoliter volume to form solids. However, 3D printing is limited to low viscosity inks that are about 10 to 100 times higher than the viscosity of water.
Viscosity is a scientific term that describes the resistance to a flow of a fluid. The fluid used can be anything from a liquid to a gas, but it is more often liquid. An example of viscosity in everyday life can be seen in pushing a spoon through a jar of honey. It takes more force and effort to move the spoon through the honey rather than in a jar of water because the honey is more resistant to the flowing around the spoon. This kind of resistance is due to the friction produced by the honey’s molecules and it affects both the extent to which the honey will oppose the spoon’s movement through it and the pressure required to make the honey move through a tube or pipe, similar to a printer.
Temperature has a large impact on viscosity which is why the measurements of viscosity for fluids always includes a temperature. In liquids, for example, it decreases with higher temperature. This is due to the fact that the molecules are moving about more, meaning that they spend less time in contact with each other.
Printing With Sound Waves
The team at Harvard created a process with the creation of sound fields that can pull substances, such as liquid metal, honey and even living cells, from the nozzle of a printer. Their process depends on the concept of gravity. After all, gravity is what causes the water from your faucet to drip. The liquid’s viscosity is what determines how fast and how often it drips. However, the more viscous a material is, the more difficult it is to use for printing. Daniele Foresti, a research associate in materials science and mechanical engineering at Harvard, stated that the team’s “goal was to take viscosity out of the picture by developing a printing system that is independent of the material properties of the fluid.”
So, the team turned to the idea of using sound as their substance. They started experimenting with how sound waves affect liquids to give gravity a little help. They used one of their own instruments, a “subwavelength acoustic resonator” to produce tightly controlled acoustic fields that ultimately increased the relative gravity near the printing nozzle. This entire process was able to create pulling forces that were “100 times the normal gravitation forces (1G) of the printer nozzle,” according to the news release. Those pulling forces were four times the gravity of the sun. Based on the team’s notes, the size of the droplet was determined by the amplitude of the soundwave. In other words, the higher the amplitude, the smaller the drop.
Foresti also believes that the viscosity of the fluid no longer matters when sound waves are present. This will ensure that temperature won’t have as much impact on the size of droplet produced. “The idea is to generate an acoustic field that literally detaches tiny droplets from the nozzle, like picking apples from a tree.”
A Huge Step For The Future
This study not only proved that it is possible to print using sound waves but also that it can be used with living cells. The researchers from Harvard discovered during their testing that the sound waves do not travel through the droplet, so this method is safe to use with sensitive biological cargo like living cells or proteins. It could be a huge help for medical teams in the future if they can figure out how to use this safely in procedures as well as in orthopedic surgery. As early as the early two-thousands, 3D printing technology has been studied and observed by the biotech firms for possible use in tissue engineering applications where organs and body parts are built using inkjet. Bio-printing will have the brightest future with help from the Harvard team’s research because it involves layers of living cells that are deposited onto a gel medium and are slowly built up to form three dimensional structures. Their research will ensure that the living cells are not damaged during the printing process.
3D printing has also been used in education, rapid manufacturing, automotive industries, rapid prototyping, aviation, aerospace, construction, architecture, consumer products, and other industries. Jennifer Lewis is the senior author and the Hansjorg Wyss Professor of Biologically Inspired Engineering at SEAS and she has a lot of hope for their technology. “Our technology should have an immediate impact on the pharmaceutical industry. However, we believe that this will become an important platform for multiple industries.” The process of acoustophoretic printing may be another step closer to making a replicator for food or other biological substances. The possibilities with this kind of discovery are endless.