Sheath‐assisted microfluidics for elasto‐inertial manipulation of micro/nanoparticles: From theory to biomedical applications

Abstract Bioparticle manipulation is vital for diagnostics, therapeutics, and biological research. Microfluidic technology provides high throughput and precise control, yet traditional methods using Newtonian fluids face challenges like cell damage due to high flow rates, and inefficient submicron sorting. To address these limitations, the introduction of viscoelastic fluids enables scale‐dependent particle sorting without external fields. Nevertheless, unitary viscoelastic flow systems fail to meet clinical‐grade bioparticle manipulation requirements due to limitations such as poor focusing stability, inadequate adaptability to complex biological samples, and low cross‐scale sorting efficiency. To overcome these issues, a sheath‐assisted strategy is employed to regulate fluid interfaces via a multiflow laminar flow mechanism. In this process, the sheath‐assisted elasto‐inertial effect compresses particle migration paths and enhances micro/nanoscale particle manipulation efficiency. This review systematically elucidates the core principles and advantages of sheath‐assisted viscoelastic microfluidics through theoretical modeling, parametric analysis, mechanistic elucidation of interfacial effects, and biomedical application cases. It would pave the way for breakthroughs in precision diagnostics, nanomedicine, and personalized therapeutics, ultimately unlocking unprecedented insights into life from microscale to nanoscale.