The engineers suggest that producing 3D shapes at the micro-scale could be useful for designing custom biomaterials such as interlocking particles that self-assemble to help tissue regenerate, or for industrial applications such as creating coatings and paints with unique light-reactive properties.
Dino Di Carlo, professor of bioengineering at UCLA, said: “We know that shape often determines material function, so while we have a few ideas of what this could lead to, this fundamental capability to produce made-to-order 3D microparticles could be applied in ways we have not contemplated.”
While traditional 3D printing methods can make shapes with incredible complexity, researchers have not been able to make similarly complex objects smaller than a millimetre because the drops of material are too big.
To make smaller custom objects with folds, holes and other precise features, the UCLA team developed a technique called optical transient liquid modelling. It uses a series of microfluidic and optical technologies that simplifies designing the shape of fluid flows.
First, two different types of fluids are combined in a series of tiny pillars that control the shape of the merged fluids. One fluid is a liquid polymer that is the precursor material for the object. The other acts as a liquid mould for the polymer stream. The arrangement of the pillars determines how the two flows mix and intertwine. The researchers used software that they previously developed to predict what shape will be produced by altering the pillars’ location and sequence.
When the flow of materials is stopped rapidly, an outlined pattern of ultraviolet light slices into the precursor stream, the object is shaped first by the stream, then again by UV light.
“It’s like we squeeze dough through a mould - the liquid mould - to make a noodle and then cut the noodle into pieces using another mould - the patterned UV light,” said Chueh-Yu Wu, the lead author of the research and a graduate student in Di Carlo’s lab.
The objects the team has produced are about 100 to 500µm in size, with features as small as 10 to 15µm. With this method, they have produced objects composed of organic materials as well as particles whose movements and position could be controlled by magnetism.
