Thiolation of polycaprolactone (PCL) nanofibers by inductively coupled plasma (ICP) polymerization: Physical, chemical and biological properties

In this study, polycaprolactone (PCL) nanofibrous mats (empty set: 144.2 +/- 3.4 nm) were fabricated by electrospinning and subsequently exposed to a low-pressure plasma polymerization treatment using 1-propanethiol as monomer. Surface characterization was performed utilizing several techniques: X-ray photoelectron spectroscopy (XPS) for surface chemical analysis, water contact angle (WCA) measurements for wettability examination, scanning electron microscopy (SEM) for morphological characterization as well as atomic force microscopy (AFM) for visualization of the topography of individual nanofibers before and after the plasma polymerization process. Moreover, the biocompatibility of the untreated and plasma-modified nanofibers was also evaluated by seeding bone marrow stem cells (BMSTs) on the samples and examining cell adhesion and proliferation using live/dead fluorescence imaging and MTT assays. The obtained results revealed that plasma exposure time significantly affected the morphology as well as the surface chemical composition of the electrospun mats, while surface wettability was largely maintained. A short exposure time of 5 s was found to maintain the advantageous nanofibrous morphology as only a very thin coating layer was deposited (range of a few nms), while longer exposure times resulted in a gradual loss of the nanofibrous structure due to the inhomogeneous deposition of thicker coatings. Moreover, also the sulphur amount was found to gradually increase with increasing exposure time resulting from the gradual growth of the deposited thiol-rich coating on the nanofibers with a maximum of 14% of sulphur, correlating with a 6.7% -SH concentration after a plasma polymerization step of 1 min. As the nanofibrous structure is highly advantageous for cell growth, a 5 s plasma exposure time was selected for the cell studies, which proved that the deposition of a very thin thiol-rich coatings was able to positively affect BMSTs adhesion and proliferation. These enhanced cellular responses can be attributed to the presence of thiol groups on the nanofibers which are known to significantly increase the adhesion of culture medium proteins. It can thus be concluded that the incorporation of thiol functionalities via plasma polymerization can positively affect the cellular response of nanofibrous meshes and thus have large potential in tissue engineering applications.