3D Reconstruction of Bias Effects on Porosity, Alignment and Mesoscale Structure in Electrospun Tubular Polycaprolactone

TL;DR

This study investigates how collector bias influences the 3D porosity, surface roughness, and fiber alignment in electrospun polycaprolactone scaffolds, revealing novel mesoscale features and a new electric field model for fiber orientation control.

Contribution

It introduces a comprehensive 3D analysis of bias effects on scaffold structure and develops a modified electric field model to predict fiber alignment in cylindrical electrospinning.

Findings

Porosity decreases with increasing bias, from 91.1% to 80.2%.

Mesoscale surface roughness features are bias-dependent, shrinking and disappearing at higher bias.

Modified electric field model explains fiber alignment along the mandrel axis.

Abstract

Porosity variations in tubular scaffolds are critical to reproducible, sophisticated applications of electrospun fibers in biomedicine. Established laser micrometry techniques produced ~14,000 datapoints enabling thickness and porosity plots versus both the azimuthal (Phi) and axial (Z) directions following cylindrical mandrel deposition. These 3D datasets could then be "unrolled" into "maps" revealing variations in thickness and porosity versus 0, -5, and -15 kV collector bias. As bias increases, thinner, more "focused" depositions occur. Simultaneous decreases in net porosity versus bias (91.1% 0kV > 83.4% -5kV > 80.2% -15 kV) are sensible, but significant changes in the distribution were unexpected. Surprisingly, at 0 kV, extensive mesoscale surface roughness is evident. Optical profilometry revealed unique features ~1600-420 mum in size, standing ~210 mum above the surrounding surface. These shrink to only ~440-150 mum in size and ~30 mum higher at -5 kV bias and disappear entirely at -15 kV. Scanning electron microscopy (SEM) resolved these into novel, localized "domains" containing tightly aligned fibers oriented parallel to the mandrel axis. Unexpectedly, we also observed substantial orientation along the mandrel axis. By modifying classical bending instability models to incorporate cylindrical electric fields, simulation revealed that horizontal components in the modified electric field alter bending loop shape, causing the observed alignment. This provides a new, easily utilized tool enabling facile, efficient tuning of orientation.