Kai Melde, MPI for Medical Research, Heidelberg University
The use of sound waves to create a pressure field to print particles.
Scientists from the Micro, Nano, and Molecular Systems Lab at the Max Planck Institute for Medical Research and the Institute for Molecular Systems Engineering and Advanced Materials at Heidelberg University have created a new technology to assemble matter in 3D.
Their concept uses acoustic holograms to generate pressure fields with which solid particles, gel beads, and biological cells can be printed. The team says the results ‘pave the way’ for novel 3D cell culture techniques with applications in biomedical engineering.
“We were able to assemble microparticles into a three-dimensional object within a single shot using shaped ultrasound,” said Kai Melde, postdoc in the group and first author of the study.
Peer Fischer, Professor at Heidelberg University, said: “This can be very useful for bioprinting. The cells used there are particularly sensitive to the environment during the process.”
Using high frequency ultrasound, which is inaudible to the human ear, wavelengths can be pushed below a millimetre into the microscopic realm, which is used by the researcher to manipulate very small building blocks, like biological cells.
In 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. Those sound fields were demonstrated by the team as being able to assemble materials into 2D patterns. Based on this, the scientists devised a new fabrication concept.
The new study allowed the team to take the idea a step further. Particles and cells freely floating in water are captured and assembled into 3D shapes. The new method works with a variety of materials according to the researchers, including glass or hydrogel beads and biological cells.
First author Kai Melde said: “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 optimise the hologram field, added: “The digitisation of an entire 3D object into ultrasound hologram fields is computationally very demanding and required us to come up with a new computation routine.”
The scientists believe the technology is a promising platform or the formation of cell cultures and tissues in 3D. The team says that ultrasound provides an advantage of being gentle for using biological cells, as well as having the benefit of being able to travel deep into tissue, and this way it can be used to remotely manipulate and push cells without harm.
