Sorting directionally oriented microstructures using railed microfluidics

We demonstrate the microfluidic sorting of directionally oriented (anisotropic) microstructures by their orientational state in solution using the concept of railed microfluidics. After being injected into a microfluidic channel, the microstructures rotate and flip in various directions. In order to sort microstructures in an organized way, we designed the microstructures and the microchannel to allow for orientation-based control of microstructure movement. In order to sort microstructures based on their rotation, we used a wedge shaped fin on the microstructures and a Y-shaped railed microfluidic channel. For sorting flipped particles, we use a double-railed microfluidic channel that has grooves on both its top and bottom surfaces. By integrating the two sorting methods we demonstrated high throughput, autonomous sorting into four different orientational states: unrotated–unflipped, rotated–unflipped, unrotated–flipped, and rotated–flipped. Here we not only demonstrate orientational assembly of directionally dependent microstructures, but also present design considerations for future work.