Surface modification of electrospun polycaprolactone microfibers by air plasma treatment: Effect of plasma power and treatment time

[Display omitted] •Electrospun PCL nanofibers were superficially modified by air plasma treatment.•Effect of power level and discharge times on physicochemical properties was studied.•Surface changes were followed by FTIR, EDX, XPS, SEM, AFM, contact angle and o-TBO.•Carboxyl groups measured by XPS were correlated with those obtained by TBO analysis. Polycaprolactone (PCL) is a biocompatible polymer approved by the FDA for using in medical devices but it is generally considered as hydrophobic material. In order to improve this drawback, electrospun PCL microfibers were superficially modified by air plasma treatments at three power levels (10, 20, 30W) and three discharge times (1, 3, 5min). The changes undergone by the microfibers were followed using spectroscopic and microscopic techniques such as Fourier Transform Infrared Spectroscopy (FTIR), Energy-dispersive X-ray spectroscopy (EDX), X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM); contact angle and surface energy were also determined and the concentration of carboxylic groups was estimated by means of the o-toluidine blue method (TBO). SEM and AFM images demonstrated that the electrospun microfibers did not suffer morphological or topographical changes after the treatment. The contact angle in water diminished, whereas with diiodomethane, it increased after air plasma treatment. FTIR spectra did not show evidence that the plasma treatment modified the surface chemical composition of the microfibers, although the results from EDX and XPS showed an increase in oxygen–containing species and in the O/C ratio after treatment. Deconvolution of the O1s signals in the XPS spectra demonstrated that the carboxylic groups (COOH) increase with treatment time, which was confirmed and quantified with the TBO method. The percentage of the COOH groups measure by XPS was correlated with the concentration obtained in the TBO analysis.