Development of 1-propanethiol-based thiol-rich plasma polymerized coatings using a medium pressure dielectric barrier discharge

Abstract

In this study, a dielectric barrier discharge (DBD) plasma at medium pressure has been utilized for the deposition of thiol-rich nano-coatings on polystyrene (PS) substrates using 1-propanethiol. The effects of working pressure (5–20 kPa), treatment time (0.5–5 min) and a subsequent Ar plasma activation step on the deposited films properties have been explored. Several characterization techniques including X-ray photoelectron spectroscopy (XPS), water contact angle goniometry (WCA), scanning electron microscopy (SEM) and atomic force microscopy (AFM) were employed to characterize the effects of the processing parameters on film thickness, coating stability, wettability, chemical composition and -SH retention. Possible changes in biocompatibility were also evaluated through in-vitro analyses involving mouse calvaria 3T3 (MC3T3) cells for which cell adhesion was studied by live/dead fluorescence imaging and MTT assays. Through controlled variation of the processing parameters, significant changes in coating topography, thickness, surface chemical composition and wettability were induced, showcasing a high control and tunability of the deposition process and resulting in smooth coatings with a sulphur content of over 20% and a thiol selectivity of 50–56%, surpassing the thiolation efficiency of the current state of the art plasma deposition technology. The coating stability was found to drastically improve after applying the secondary plasma activation step, a phenomenon that was attributed to the removal of low MW species in combination with progressive cross-linking and oxygen polar group incorporation. The significant increase in -SH deposited on PS resulted in a notable increase in cell viability (45%) compared to its pristine counterparts. Cell-surface interactions did not vary significantly as a function of coating thickness, despite slight variations in thiol selectivity for increasing deposition times. Overall, it seems that the deposition of 1-propanethiol-based coatings using a medium pressure parallel-plate DBD leads to thiol-rich thin films that can positively affect cell-surface interactions, therefore exhibiting a large potential for tissue engineering applications.