Preface: The Engineering of Microscopic Structures
If nanofibers can be likened to microscopic "cables," then embedding different functional modules within these threads—measuring just hundreds of nanometers to a few micrometers in diameter—constitutes a form of precision surgery in materials science. As traditional single-nozzle electrospinning falls short of meeting modern industry's demand for complex functional materials, coaxial electrospinning has emerged as the "scalpel" in researchers' hands. This technology not only transforms fiber morphology but fundamentally redefines material composition logic, unlocking possibilities in biomedicine, energy conversion, and smart sensing.
Breaking Boundaries: Overcoming Single-Material Limitations
While conventional electrospinning efficiently produces nanofibers, its single-component solution process yields homogeneous structures that limit multifunctional applications. Coaxial electrospinning revolutionizes this through specialized nozzle designs, enabling simultaneous ejection of multiple polymer solutions to create hollow, core-shell, and multi-core architectures at the nanoscale.
The breakthrough lies in "functional nesting." Many high-performance components—such as fragile enzymes, unstable oligomers, reactive metal nanoparticles, or salts—often degrade during traditional spinning due to solvent toxicity or shear forces. The coaxial approach encapsulates these sensitive elements within protective polymer sheaths. In biomedicine, for instance, core-shell structures enable precise drug release: protected by the polymer shell, therapeutic agents resist gastric acid or enzymatic degradation while achieving controlled release, significantly enhancing bioavailability.
The Art of Structural Design: From Islands to Side-by-Side Configurations
The technology's versatility allows unprecedented spatial freedom, moving beyond simple core-shell arrangements:
- Island-in-Sea Architecture: Multi-core designs where a single fiber contains numerous micro-cores. Combining tough "sea" polymers with strong "island" materials like carbon nanotubes yields fibers with both flexibility and exceptional strength. In drug delivery, multiple cores enable co-loading of different therapeutics for staged, multi-target treatments.
- Side-by-Side Structures: Parallel distribution of two materials within a fiber cross-section creates anisotropic functionality. Pairing conductive and insulating polymers forms microscopic circuitry, while hydrophilic/hydrophobic Janus fibers excel in microfluidics and self-driven liquid transport systems.
The Invisible Hand: Gas-Assisted Precision Control
Fiber morphology control proves challenging, especially with volatile or viscous systems. Gas-assisted coaxial electrospinning introduces an airflow "invisible hand" through outer nozzles, serving multiple purposes: accelerating solvent evaporation to prevent fiber adhesion, enhancing jet stretching for finer diameters, and creating a protective barrier against nozzle clogging. This method demonstrates remarkable robustness for industrial-scale production.
Hollow Nanofibers: Logic and Applications
Critical for hydrogen storage, nanofluidics, and catalyst supports, hollow fibers achieve superior fabrication efficiency compared to chemical vapor deposition. The "sacrificial template" approach uses volatile or soluble core solvents that evaporate post-spinning, leaving precisely dimensioned cavities. In lithium-ion batteries, such structures mitigate electrode expansion during cycling, significantly extending battery life.
Core Hardware: The Philosophy of Nozzle Design
Nozzle quality dictates experimental success in coaxial electrospinning. Medical-grade 304/316L stainless steel spinnerets prioritize:
- Precise Concentricity: Ensures uniform core distribution through precision machining that maintains laminar flow, preventing structural defects.
- Modular Maintenance: Detachable designs facilitate cleaning and material switching, reducing contamination risks during polymer processing.
- Sealed High-Pressure Operation: PTFE gaskets prevent solution leakage under electric fields, while nozzle sizes (5-28 gauge) accommodate diverse fiber scales.
Future Horizons: From Lab to Industry
Evolving from experimental technique to precision nanomanufacturing, coaxial electrospinning's future focuses on:
- Smart Integration: Merging with microfluidics for real-time structural control to create "sense-and-respond" functional fibers.
- Multiscale Production: Nozzle arrays to overcome throughput limitations for filtration materials and medical textiles.
- Sustainable Manufacturing: Developing eco-friendly solvent systems to reduce VOC emissions.
As a bridge between microstructure and macroscopic performance, coaxial electrospinning continues expanding humanity's mastery over materials science. In the nanoworld, each fiber holds infinite potential—and this technology provides the key to unlock it.
