Droplet splitting in microfluidics: A review

Abstract

Droplet microfluidics enables precise control of microscale fluids, facilitating advancements in biomedical diagnostics, single-cell analysis, and high-throughput screening. Among its core functions, droplet splitting within microfluidic systems is critical for controlling reaction volumes, concentration gradients, and sequential fluidic processes. Despite its widespread application, no comprehensive review has systematically examined microfluidic droplet splitting. This review bridges this gap by correlating experimental findings with theoretical models, offering a structured assessment of existing methodologies. The splitting process is primarily dictated by interfacial forces, viscous forces, and inertial effects, with the capillary number (Ca) as a key dimensionless parameter defining its dynamics. This review classifies droplet splitting approaches into passive and active techniques. Passive methods, which depend on channel geometries and hydrodynamic conditions, primarily involve T-junctions and Y-junctions. Active techniques allow tunable droplet control through external forces, including pneumatic, acoustic, electric, magnetic, and thermal actuation. A comparative overview highlights differences in efficiency, selectivity, scalability, and energy demand. While passive techniques offer simplicity and robustness, active approaches enable greater adaptability in real-time applications. Challenges persist in achieving precise volume control, seamless integration with automated workflows, and high-throughput reproducibility. Future research should explore biocompatible actuation strategies and MHz-frequency splitting to enhance lab-on-a-chip technologies. By integrating fluid mechanics principles with emerging microfluidic innovations, this review establishes a comprehensive framework for optimizing droplet splitting in scientific, interdisciplinary, and industrial applications.

Topics & Concepts