🧱 Electrospun Nanofiber Scaffold Mechanical Property Tuning

Loading and Charging the Polymer Solution

Electrospinning begins with a spinnable polymer solution held at a syringe tip and subjected to a strong electric field, priming it for jet formation.

• 10–30: Applied Voltage (kV, typical range)
• 5–20: Polymer Conc. (% w/v in solvent)
• 10–25: Tip-Collector Gap (cm)
• 4+: Common Polymers (PCL, PLGA, collagen, silk)

The Feedstock

A polymer such as poly(caprolactone) (PCL), poly(lactic-co-glycolic acid) (PLGA), collagen, gelatin, or silk fibroin is dissolved in a volatile solvent at a concentration high enough to entangle polymer chains — a prerequisite for forming continuous fibers rather than droplets (electrospraying).

Applying the Field

A high-voltage power supply (10–30 kV) connects to the needle or the solution itself, while the collector is grounded. The resulting electric field induces a net charge on the pendant droplet at the needle tip, held there by surface tension and the syringe pump's steady flow.

From Droplet to Charged Jet

Electrostatic repulsion within the droplet grows until it overwhelms surface tension, reshaping the droplet into a cone and launching a jet from its tip.

• 49.3°: Taylor Cone Angle (theoretical half-angle)
• ~6–10: Critical Voltage (kV onset threshold)
• 1–10: Initial Jet Diameter (µm at cone apex)
• 0.5–5: Flow Rate (mL/hr)

Force Balance

As voltage increases, the mutually repulsive charges on the droplet surface exert an outward electrostatic force that competes with the inward pull of surface tension. Past a critical voltage this balance breaks, deforming the hemispherical droplet into a sharp, conical point known as the Taylor cone.

Jet Initiation

A fine, charged jet erupts from the Taylor cone apex and accelerates toward the grounded collector, driven by the field. In this initial segment the jet travels in a straight, stable line before instabilities take over.

The Bending Instability that Makes Nanofibers

A rapid, chaotic whipping motion stretches the jet by orders of magnitude, thinning it from microns down to nanometers as the solvent flashes off.

• ~10⁵×: Stretch Ratio (jet elongation factor)
• 50 nm–5 µm: Final Diameter (typical fiber range)
• <1: Flight Time (second, tip to collector)
• >90%: Solvent Loss (evaporated in flight)

Bending Instability

Small perturbations in the straight jet segment grow explosively into a fast, looping whipping motion. Each loop stretches the jet further, and the loops themselves generate smaller sub-loops in a self-similar cascade, multiplying the total path length the jet travels before landing.

Evaporation and Solidification

The enormous increase in surface area during whipping accelerates solvent evaporation. By the time the jet reaches the collector, most of the solvent has left and the polymer has solidified into a continuous solid nanofiber.

Collector Geometry Controls Fiber Architecture

The collector's shape and motion determine whether fibers land as a random tangled mesh or as parallel, mechanically anisotropic bundles.

• 1,000–10,000: Rotating Mandrel Speed (RPM for alignment)
• 70–90%: Random Mesh Porosity (void fraction)
• <10°: Aligned Fiber Angle Spread (from rotation axis)
• 10–500: Mesh Thickness (µm typical)

Collector Strategies Compared

A Cell-Instructive, ECM-Mimetic Mesh

The finished nanofiber mat combines high surface area, tunable porosity, and — when aligned — directional mechanics that actively guide cell behavior.

• 10–100×: Surface Area / Volume (vs. solid film)
• 1–100: Elastic Modulus (MPa, tunable)
• µm–mm: Cell Infiltration Depth (set by pore size)
• ~50–500 nm: Fiber-Collagen Similarity (native fibril range)

Structural Mimicry

Because nanofiber diameters (tens to hundreds of nanometers) fall within the same range as native collagen fibrils, cells seeded on the mesh encounter a topography and surface curvature close to their natural ECM environment, promoting attachment and spreading.

Function Follows Architecture

Random meshes provide isotropic mechanical support suited to skin and generic soft tissue. Aligned meshes provide anisotropic tensile strength along one axis and physically channel cell migration and elongation along that axis — critical for regenerating directional tissues like tendon, ligament, and peripheral nerve.