Effects of Humidity and Solution Viscosity on Electrospun Fiber Morphology

Abstract

Electrospinning is a popular technique to fabricate tissue engineering scaffolds due to the exceptional tunability of fiber morphology that can be used to control scaffold mechanical properties, degradation rate, and cell behavior. Although the effects of modulating processing or solution parameters on fiber morphology have been extensively studied, there remains limited understanding of the impact of environmental parameters such as humidity. To address this gap, three polymers (poly(ethylene glycol) [PEG], polycaprolactone [PCL], and poly(carbonate urethane) [PCU]) were electrospun at a range of relative humidities (RH = 5%-75%) and the resulting fiber architecture characterized with scanning electron microscopy. Low relative humidity ( < 50%) resulted in fiber breakage for all three polymers due to decreased electrostatic discharge from the jet. At high relative humidity ( > 50%), three distinct effects were observed based on individual polymer properties. An increase in fiber breakage and loss of fiber morphology occurred in the PEG system as a result of increased water absorption at high relative humidity. In contrast, surface pores on PCL fibers were observed and hypothesized to have formed via vapor-induced phase separation. Finally, decreased PCU fiber collection occurred at high humidity likely due to increased electrostatic discharge. These findings highlight that the effects of relative humidity on electrospun fiber morphology are dependent on polymer hydrophobicity, solvent miscibility with water, and solvent volatility. An additional study was conducted to highlight that small changes in molecular weight can strongly influence solution viscosity and resulting fiber morphology. We propose that solution viscosity rather than concentration is a more useful parameter to report in electrospinning methodology to enable reproduction of findings. In summary, this study further elucidates key mechanisms in electrospun fiber formation that can be utilized to fabricate tissue engineering scaffolds with tunable and reproducible properties.

Activated Schwann Cell-Like Cells on Aligned Fibrin-Poly(Lactic-Co-Glycolic Acid) Structures: A Novel Construct for Application in Peripheral Nerve Regeneration

“…The choice of polymer solution (fibrin or fibrin-PLGA) as well as the ambient parameters temperature and humidity are important factors that affect the spinning quality [Nezarati, 2013].…”

Conductive PANI fibers and determining factors for the electrospinning window

“…In the case of electrospinning poly-carbonate urethane, fibre collection dropped at high humidity, most likely due to increased electrostatic discharge. In the same study, humidity below 50% resulted in fibre breakage due to decreased electrostatic discharge from the jet for all three polymers that were electrospun (Polyethylene glycol, poly carbonate urethane and polycaprolactone) [13,15,16]. Tripatanasuwan et al concluded that there is a linear decrease of the diameter of PEO fibres with increasing humidity.…”

“…Even if in all the solutions studied, the general trend of the way the relative humidity affects the process was the same, there are discrepancies regarding the thresholds and quantitative results which they attributed to different polymer characteristics [14]. High humidity has also been reported to cause fibre breakage and loss of poly-ethylene glycol fibre morphology, as a result of increased water absorption [15].…”

Electrohydrodynamic direct printing of PCL/collagen fibrous scaffolds with a core/shell structure for tissue engineering applications

“…As expected, with increasing concentration of the PCL, the non-fibrous region in the cross-section of the struts was enlarged due to the increased viscosity. Generally, high viscosity (i.e., a high concentration of polymeric solution) can generate greater viscoelastic force, which prevents the whipping/stretching motion, finally inducing larger-diameter electrospun fibers versus a low concentration of polymeric solution [31][32][33]. However, at the high flow rate (1.5 mL/h), the effect of PCL concentration was negligible.…”