Design advances in pinched flow fractionation for enhanced particle separation in microfluidics

Pinched flow fractionation (PFF) is a simple, biocompatible microfluidic technique for particle separation, well-suited for applications requiring easy design, ease of operation, and gentle sample handling. In this review, we systematically summarize design advances in PFF, categorizing innovations into five core strategies: broadened segment optimization, pinched segment modification, outlet design refinement, active method integration, and passive hybridization. Both the optimized designs and their underlying working mechanisms are elucidated. While PFF inherently operates as a size-based separation method, these developments have expanded its applicability to shape- and density-based separations. Key performance enhancements are highlighted, e.g., modifications to the pinched and broadened segments increase separation distance, microvalve-integrated outlets enable real-time control, active method integration improves separation resolution, and inertial microfluidic hybridization enhances throughput. Besides, we review representative applications of PFF, like the separation of extracellular vesicles for immunoblotting and microplastics for water quality evaluation. Design guidelines promoting the separation performance are discussed, alongside potential biological particle targets and a comparative analysis of PFF and other separation techniques. Finally, future directions are proposed, emphasizing the integration of passive methods and device parallelization to maintain PFF's simplicity while improving throughput and separation capabilities. This review aims to provide theoretical insights and technical guidance for continuous innovation in PFF, promoting its practical implementation across biomedical and environmental monitoring fields.