Researchers from Delft and Utrecht separate microparticles on the basis of their shape

Scientists in Delft and Utrecht have developed a technique for selectively separating microparticles in a liquid on the basis of their shape, by only using the flow through a wide but shallow tube. The experiments done in Delft confirm the calculations done in Utrecht, which specify the path that a specifically shaped microparticle will take through the tube. This makes it possible to set up a sorting channel in which the differently shaped particles each find their own way.

Up to now, separating particles from a fluid based has only been possible based on their size or by using an external source such as a light, magnetic or electric field. The new technique, which was published today in PNAS, can be used in a range of sectors, for example in the manufacture of medicines. Principal investigator H. Burak Eral (TU Delft and Utrecht University): “During the production process, tiny variations can trigger formation of undesired crystal forms with distinct shapes and structure, that are of the same size as desired ones. This new technique makes it possible for us to remove the undesired, potentially harmful crystals from the liquid.”

Theoretical predictions

Earlier research had already shown that the asymmetrical particles flow in a particular way through a wide but shallow channel. “Although the particles tumble in a complex manner and are swept along by the flow, it proved possible to make concrete theoretical predictions on the path they would follow,” says Prof. René van Roij, who supervised PhD candidate Bram Bet and postdoc Sela Samin in making the calculations in 2018.

The researchers at TU Delft used these calculations in their continued work on experiments, 3D simulations and the theory, to gain an in-depth understanding of the pattern of the microparticles. They were eventually able to reduce the pattern to a universal formula in which the only variable is the shape of the particle.

Publication

Universal motion of mirror-symmetric microparticles in confined Stokes flow
Rumen N. Georgiev, Sara O. Toscano, William E. Uspal, Bram Bet*, Sela Samin*, René van Roij*, and Huseyin Burak Eral*
Proceedings of the National Academy of Sciences Aug 2020, 202005068; DOI: 10.1073/pnas.2005068117
* researchers affiliated with Utrecht University