A microfluidic band-pass filter for flexible fiber separation

Flexible fibers are common in nature and technology, from biological filaments to nanomaterials and pollutants. However, sorting these deformable, anisotropic objects in flow remains difficult. We show that microfluidic devices with tilted pillar arrays-originally designed for spherical particles-can be adapted to separate fibers by length. Unexpectedly, these arrays act as band-pass filters, causing lateral migration only for fibers whose lengths match the interpillar spacing. This selectivity arises from a complex interplay between fiber deformation, tension from the flow, and interactions with obstacles. Our findings reveal a physical mechanism for controlling the transport of soft, elongated objects and open possibilities for precision sorting in fields like biotechnology, environmental science, and materials engineering.

Reference :
Z. Li, C. Bielinski, A. Lindner, B. Delmotte, & O. du Roure, A microfluidic band-pass filter for flexible fiber separation, Proc. Natl. Acad. Sci. U.S.A. 123 (6) e2520537123, https://doi.org/10.1073/pnas.2520537123 (2026).