Atmospheric Pressure Plasma Jet Treatment of Poly-ε-caprolactone Polymer Solutions To Improve Electrospinning

Abstract

An atmospheric pressure plasma jet (APPJ) specifically designed for liquid treatment has been used in this work to improve the electrospinnability of a 5 w/v % solution of poly-ε-caprolactone (PCL) in a mixture of chloroform and N,N-dimethylformamide. Untreated PCL solutions were found to result in nonuniform fibers containing a large number of beads, whereas plasma-treated solutions (exposure time of 2-5 min) enabled the generation of beadless, uniform nanofibers with an average diameter of 450 nm. This enhanced electrospinnability was found to be mainly due to the highly increased conductivity of the plasma-modified PCL solutions. Consequently, more stretching of the polymer jet occurred during electrospinning, leading to the generation of bead-free fibers. Plasma treatment also results in an increased viscosity and decreased pH values. To explain these observed changes, optical emission spectroscopy (OES) has been used to examine the excited species present in the APPJ in contact with the PCL solution. This study revealed that the peaks attributed to H, CH, CH, and C species could be responsible for the degradation of solvent molecules and/or PCL structures during the plasma treatment. Size exclusion chromatography and X-ray photoelectron spectroscopy results showed that the molecular weight and the chemical composition of PCL were not significantly affected by the APPJ treatment. Plasma exposure mainly results in the degradation of the solvent molecules instead of modifying the PCL macromolecules, preserving the original polymer as much as possible. A hypothesis for the observed macroscopic changes in viscosity and pH values could be the generation of new chemical species such as HCl and/or HNO. These species are characterized by their high conductivity, low pH values, and strong polarity and could enhance the solvent quality for PCL, leading to the expansion of the polymer coil, which could in turn explain the observed enhanced viscosity after plasma modification.

Fabrication of PEOT/PBT Nanofibers by Atmospheric Pressure Plasma Jet Treatment of Electrospinning Solutions for Tissue Engineering

“…The plasma source used in this work to treat PEOT/PBT polymer solutions is an APPJ specifically designed for liquid treatment and is schematically represented in Figure 1 . The setup was already described in detail in previous work . In short, the plasma is generated inside a thin quartz capillary fed by an argon flow.…”

“…followed a similar strategy, using an atmospheric pressure plasma jet (APPJ) to treat polylactic acid dissolved in dichloromethane and observed 100% bead‐free fibers . In our research group, an extensive study on the effects of NTP exposure on a solution of PCL or PLLA in CHCl 3 and DMF was recently performed . It was found that the plasma was responsible for improving the conductivity of the polymer solution as well as changing the viscosity and pH via the generation of new chemical species without damaging the macromolecular structure of the polymer …”

“…Without the addition of HFIP to chloroform, independent of the used electrospinning parameters, it has not been possible so far to obtain continuous bead‐free nanofibers. Driven by the need to find more effective, eco‐friendly, and biomedically benign strategies to improve the electrospinning process, several research groups have been investigating the potential of using atmospheric pressure plasma to improve polymer solution properties prior to electrospinning . The exposure of solids to non‐thermal plasma (NTP) is well described and has found a widespread use in many disciplines .…”

“…However, the use of NTP to alter the properties of polymeric solutions (for electrospinning) is a field of research that has barely been touched upon. So far, to the best of the author's knowledge, only five research papers have been published that deal with this subject . Shi et al.…”

“…Successively, a mixture of chloroform and DMF (10 v/v%) was also explored as DMF has a high dielectric constant and aprotic properties, which could positively affect PEOT/PBT electrospinnability. In addition, the mixture CHCl 3 + DMF has already been extensively studied in our previous works focusing on PCL and PLA with successful electrospinning results . Third, a mixture of chloroform and MeOH (10 v/v%) was examined as methanol is also characterized by a high dielectric constant and presents a protic behavior and may thus positively affect PEOT/PBT electrospinnability.…”