Plasma treatment effects on bulk properties of polycaprolactone nanofibrous mats fabricated by uncommon AC electrospinning : a comparative study

The prominent success of polycaprolactone (PCL) electrospun nanofibrous mats (ENM) has expanded the use of PCL over other polymers for tissue engineering applications. However, the major challenge in the design of a nanofibrous scaffold is to modify its surface properties while preserving its bulk properties. Therefore, the first part of the study is focused on the fabrication of PCL-ENMs by alternating-current electrospinning using the following solvent systems: formic acid, formic acid/acetic acid (1/1) and formic acid/acetic acid/acetone (1/1/1). While the second part is focused on an nm-thick surface chemical modification via medium pressure argon and nitrogen plasma treatment, and the third part is dedicated to investigating the morphology, wettability, surface functional groups, crystallite size, crystallinity, crystallization, and melting temperature of plasma-treated nanofibers. Samples were characterized using scanning electron microscopy (SEM), water contact angle analysis (WCA), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), and differential scanning calorimetry (DSC). WCA and SEM results showed that plasma treatments significantly improve the wettability of the PCL ENMs without compromising their surface morphology. XPS analysis revealed that argon and nitrogen gases are responsible for a substantial increase in polar oxygen and nitrogen functional groups respectively. Out of the six plasma-treated PCL ENMs understudy, the argon plasma-treated sample showed superior hydrophilicity (from 136° to ~35°) followed by nitrogen plasma treatment (from 136° to ~42°). It was also found from XRD that the crystallite size was not significantly affected by the conducted plasma treatments. Moreover, the degree of crystallinity was also not altered by the plasma treatments, as was observed by DSC and FTIR. The conducted experiments showed that the surface properties of the PCL ENMs could be positively affected while maintaining their beneficial bulk properties thereby making these plasma-modified ENMs excellent candidates in multiple biomedical and tissue engineering applications.