WHY THIS MATTERS IN BRIEF
As 3D printing becomes more popular the ability to control the size of droplets opens the door to 3D printing everything from cosmetics and materials, to pharmaceutical drugs.
Harvard University has announced that its researchers have developed a way to print objects using sound. Called 3D Acoustic Printing, the method “could enable the on demand 3D printing of many new Bio-Pharmaceuticals, cosmetics, drugs, food, and material products, and expand the possibilities of 3D printing optical and conductive materials,” according to the press release. Food such as 3D printed Raspberries, that first emerged in 2014, and drugs that are more advanced than the drugs that some companies are already 3D printing for hospitals.
Printing with liquids, such as ink, has become a way of life thanks to the inkjet printing process, but what if you wanted to 3D print living human cells, tissue or other biological materials as we’re doing on an increasingly regular basis, such as brains, bones, cartilage, hearts, skin, spines, and more? And what if you wanted to 3D print liquid metal so you could print jet engines, like GE want to, and already are?
With inkjets the ability of a printer to pull a substance out of a nozzle grinds to a halt as the substance becomes thicker, but now the team at Harvard have been able to demonstrate the “creation of sound fields that can pull viscous substances, such as liquid metal, honey and even living cells, from the nozzle of a printer.”
The process begins with gravity. Simple gravity is what causes liquid to drip. How fast or often it drips depends on its viscosity – its thickness and resistance to shearing and tensile stresses. Water, for example, is far less viscous than corn syrup. Corn syrup is far less viscous than honey. The more viscous a fluid is, the longer it takes for gravity to produce a droplet. Printing systems, such as inkjet printing, typically use a droplet method of transferring a liquid material to a medium, such as paper, and the more viscous a material is the more difficult it is to manipulate for printing.
“Our goal was to take viscosity out of the picture by developing a printing system that is independent from the material properties of the fluid,” said Daniele Foresti, a research associate in materials science and mechanical engineering at Harvard. And this is where sound comes in.
Foresti and his fellow researchers began experimenting with the pressures of sound waves on liquids in order to give gravity a helping hand. They then built a “subwavelength acoustic resonator” designed to produce tightly controlled acoustic fields that effectively increased the relative gravity at the printing nozzle.
According to the release, the researchers have been able to generate pulling forces “100 times the normal gravitation forces (1G) of the printer nozzle,” which is more than four times the gravity of the sun, and the size of the droplet is simply determined by the amplitude of the soundwave – the higher the amplitude, the smaller the drop.
Here is an explanatory video from the research team at Harvard:
“The idea is to generate an acoustic field that literally detaches tiny droplets from the nozzle, much like picking apples from a tree,” said Foresti.
So far a wide range of materials have been used to test this new printing method, including honey, stem-cell inks, bio-polymers, optical resins and liquid metals, and because sound waves don’t pass through materials, using sound to create droplets won’t harm the material itself, which is important for printing with living cells.
“Our technology should have immediate impact on the pharmaceutical industry. However, we believe that this will become an important platform for multiple industries,” said Dr. Jennifer Lewis, professor of biologically inspired engineering at Harvard, and when the technology matures it could have important ramifications for multiple industries and how we 3D print a wide variety of products in the future, from human tissues and pharmaceutical drugs, and even to commercial and military aircraft and drones, and beyond.