These are waves worth catching. Generating tiny swells in a dish of saline solution prompts beads, copper powder and even cells to assemble into a panoply of intricate patterns. It could offer a simple way to build elaborate structures that may be useful for microelectronics and making human tissue.
Many attempts at small-scale construction build structures piece by piece, which can be time-consuming for complex products. Other methods can only use specific building blocks, such as magnetic materials . Now a team led by Utkan Demirci at Stanford University in California has found a way to quickly build micro-sized structures from almost anything, using a "liquid template".
The team started by making acrylic containers, each roughly 1 centimetre by 1 centimetre, but sculpted in various shapes. They filled the containers with saline solution and connected them to a vibration generator and amplifier to create acoustic pressure .
After adding a handful of starter pieces, such as silicon chips or small plastic beads, the researchers tuned the generator to various frequencies to create waves in the solution. Depending on their surface chemistry, the added particles spontaneously collected in either the crests or the valleys. Retuning the generator let the team switch between multiple patterns.
The team also cajoled cells into forming delicate structures. To get networks of cells, scientists typically have to grow them on special scaffolding or within a gel that provides support. "We wondered if we could create tissues by using sound," says Demirci. "Acoustic forces are gentle and wouldn't harm cells."
He and his colleagues cultured mouse cells and put them in the liquid template. The cells collected into little spheres that became the building blocks of larger geometric patterns. Adding blood clotting proteins to the saline solution locked the cells in place, an approach that the team is now investigating for growing liver tissue.
The method can also create networks of cells that are a specific distance apart. Seeding tiny beads with rat nerve cells resulted in delicate shapes that could be fixed in place with a protein, allowing the researchers to study which geometries of cell networks best promote growth.
The diverse array of patterns generated by the technique and the ability to switch from one pattern to another in real time is impressive, says David Gracias at Johns Hopkins University in Baltimore, Maryland, an expert in self-assembling materials. And there's nothing fancy about the required equipment, so researchers could easily take advantage of the approach for all kinds of uses.
"It's relatively easy – I could put together the set-up with stuff I have in the lab already," says Gracias.
Journal reference: Advanced Materials, DOI: 10.1002/adma.201402079