Isolation of Urinary Extracellular Vesicles (EVs) via Hydrophobic Interaction Chromatography Using a Nylon‐6 Capillary‐Channeled Polymer (C‐CP) Fiber Column

Exosomes, a subset of extracellular vesicles (EVs) ranging in size from 30 to 150 nm, are of significant interest for biomedical applications such as diagnostic testing and therapeutics delivery. Biofluids, including urine, blood, and saliva, contain exosomes that carry biomarkers reflective of their host cells. However, isolation of EVs is often a challenge due to their size range, low density, and high hydrophobicity. Isolations can involve long separation times (ultracentrifugation) or result in impure eluates (size exclusion chromatography, polymer-based precipitation). As an alternative to these methods, this study evaluates the first use of nylon-6 capillary-channeled polymer (C-CP) fiber columns to separate EVs from human urine via a step-gradient hydrophobic interaction chromatography method. Different from previous efforts using polyester fiber columns for EV separations, nylon-6 shows potential for increased isolation efficiency, including somewhat higher column loading capacity and more gentle EV elution solvent strength. The efficacy of this approach to EV separation has been determined by scanning electron and transmission microscopy, nanoparticle flow cytometry (NanoFCM), and Bradford protein assays. Electron microscopy showed isolated vesicles of the expected morphology. Nanoparticle flow cytometry determined particle densities of eluates yielding up to 5 × 10⁸ particles mL^-1, a typical distribution of vesicle sizes in the eluate (60-100 nm), and immunoconfirmation using fluorescent anti-CD81 antibodies. Bradford assays confirmed that protein concentrations in the EV eluate were significantly reduced (approx. sevenfold) from raw urine. Overall, this approach provides a low-cost and time-efficient (< 20 min) column separation to yield urinary EVs of the high purities required for downstream applications, including diagnostic testing and therapeutics.