Researchers from the Max Planck Institute for Medical Research (HPIMR) have developed a new technology that allows the assembly of matter in 3D. The concept utilizes multiple acoustic-holograms to generate pressure field with which solid particles can be printed, as well as gel beads and biological cells. These results open the door to novel 3D cell culture methods with applications in biomedical Engineering.
Additive manufacturing 3D printing is a way to create complex parts out of functional or biological materials. Conventional 3D printing is slow because objects are built one line or one layer at time. Researchers in Heidelberg and Tübingen now demonstrate how to form a 3D object from smaller building blocks in just a single step. “We were able to assemble microparticles into a three-dimensional object within a single shot using shaped ultrasound”, says Kai Melde, postdoc in the group and first author of the study. “This can be very useful for bioprinting. The cells used there are particularly sensitive to the environment during the process”, adds Peer Fischer, Professor at Heidelberg University.
Sound waves exert forces on matter – a fact that is known to any concert goer who experiences the pressure waves from a loudspeaker. High-frequency ultrasound, which can’t be heard by the human ear but is still audible, allows wavelengths to be pushed to the microscopic realm. This is used by researchers to manipulate very small building blocks such as biological cells.
In their previous studies Peer Fischer and colleagues showed how to form ultrasound using acoustic holograms – 3D-printed plates, which are made to encode a specific sound field. They demonstrated that these sound fields can be used to create two-dimensional patterns from materials. The scientists then devised a fabrication idea based on these sound fields.
Acoustic field captures particles
The team took their idea one step further with their new study. The team captures particles and cells floating in water, and then assembles them into three-dimensional shapes. On top of that, the new method works with a variety of materials including glass or hydrogel beads and biological cells. First author Kai Melde says that “the crucial idea was to use multiple acoustic holograms together and form a combined field that can catch the particles”. Heiner Kremer, who wrote the algorithm to optimize the hologram fields, adds: “The digitization of an entire 3D object into ultrasound hologram fields is computationally very demanding and required us to come up with a new computation routine”.
Scientists believe their technology will be a promising platform to create 3D cell cultures and tissues. Ultrasound is gentle enough to use biological cells, and can penetrate tissue. It can also be used remotely to push and manipulate cells without causing harm.