Core-Shell and Coaxial Electrospinning: Advanced Nanofiber Architectures for Next-Generation Membranes

Core-Shell and Coaxial Electrospinning: Advanced Nanofiber Architectures

Coaxial electrospinning represents a significant advancement in nanofiber fabrication, enabling the production of core-shell structured fibers with distinct materials in each layer. This technique opens possibilities impossible with conventional single-nozzle spinning: sustained drug release from an encapsulated core, hollow nanofibers for catalysis, multi-functional membranes combining filtration with antimicrobial activity, and encapsulation of sensitive bioactive compounds.

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What Is Coaxial Electrospinning?

Coaxial electrospinning uses a concentric spinneret with two or more channels to simultaneously deliver different polymer solutions. The outer solution forms the shell while the inner solution forms the core. A compound Taylor cone forms at the spinneret tip, producing a co-axial jet that solidifies into core-shell nanofibers. Tri-axial spinnerets add a third intermediate layer for even more complex architectures.

Critical Process Parameters for Coaxial Spinning

The core-to-shell flow rate ratio is the most critical parameter, typically maintained between 1:2 and 1:5. The shell solution must have sufficient viscosity and chain entanglement to encapsulate the core. Viscosity matching between core and shell prevents jet instabilities. Voltage requirements are generally 15-30% higher than single-needle spinning to maintain a stable compound Taylor cone. The spinning distance should be 15-25 cm to allow complete solvent evaporation from both layers.

Applications of Core-Shell Nanofibers

Sustained drug release: hydrophobic shell controls the release rate of drugs loaded in the core, achieving near-zero-order release over weeks. Hollow nanofibers: dissolving the core after spinning creates hollow tubes with extremely high surface area for catalysis and energy storage. Bioactive encapsulation: proteins, growth factors, and enzymes protected from processing conditions in the core while the shell provides structural integrity. Multi-functional membranes: combining a filtration shell with an antimicrobial or photocatalytic core for advanced water treatment.

Emulsion Electrospinning as an Alternative

Emulsion electrospinning achieves core-shell structures using a single nozzle by spinning a water-in-oil emulsion. The aqueous phase migrates to the fiber center during spinning, forming a core-shell structure without a coaxial spinneret. This approach is simpler to implement but offers less control over core-shell dimensions than true coaxial spinning.

Characterization of Core-Shell Fibers

TEM provides direct visualization of core-shell morphology and layer thickness. Confocal laser scanning microscopy (CLSM) with fluorescent dyes in each layer confirms encapsulation. SEM-EDS maps elemental distribution across the fiber cross-section. XPS provides surface composition analysis. AFM characterizes surface mechanical properties of the shell layer.

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Tech Inc. System for Coaxial Electrospinning

The Tech Inc. Electrospinning Nanofiber Membrane Production System supports coaxial configurations with its precision syringe pump (0.1-50 mL/hr), multiple needle gauge options (18G-27G), 0-50 kV power supply, and adjustable spinning distance (5-30 cm). The enclosed environmental chamber and automatic DAQ ensure reproducible core-shell fiber production.

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Frequently Asked Questions

What is the difference between coaxial and emulsion electrospinning?

Coaxial uses a concentric spinneret with separate feeds for core and shell, giving precise control over layer dimensions. Emulsion uses a single nozzle with a water-in-oil emulsion, where phase separation during spinning creates the core-shell structure with less dimensional control.

Can hollow nanofibers be made by coaxial electrospinning?

Yes. By using a sacrificial core material (such as PVP or mineral oil) that is selectively dissolved or extracted after spinning, hollow nanofibers with controllable wall thickness and inner diameter can be produced.

What flow rate ratio works best for core-shell fibers?

A core-to-shell ratio of 1:2 to 1:5 is typical. The shell flow rate must be high enough to maintain continuous encapsulation of the core. Exact ratios depend on solution viscosities and the desired core-shell dimensions.

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