Comparison of localized treatment effectiveness on biocompatible glass with different atmospheric pressure plasma sources

Summary form only given. In recent years, increasing efforts have been dedicated to atmospheric pressure non-thermal plasma (NTP) modification of biomaterials to promote cell adhesion and proliferation; while low-pressure plasma is already an established technology in this field, NTP are raising interest because of their easy handling, effectiveness and low operational costs. Moreover, the possibility of locally modifying the surface, creating patterns to induce controlled cell growth, would be of great interest for some application of these materials. In this work NTP local modification of borosilicate glass cell culture coverslips (size 24x24 mm) has been performed with three non-equilibrium atmospheric pressure plasma sources: a single electrode plasma jet, a dielectric barrier discharge (DBD), both connected to a high voltage pulse generator, and a commercial plasma jet (kINPen 09, Neoplas Tools GmbH); surface wettability before and after plasma treatment has been studied using water contact angle (WCA) measurement. To analyze plasma treatment localization with the two different plasma jets, four regions (quadrants) were identified onto each slide and the plasma discharge was oriented towards only one of these. Results suggest a decrease of WCA in the region directly exposed to the plasma jet, while the remaining area doesn't show any significant variation of surface wettability. With these sources the localization efficiency is strongly influenced by the distance between the source outlet and the substrate: increasing the stand-off results in a more localized surface modification. While in the case of the single electrode Ar plasma jet a relevant reduction of WCA was obtained only in the region exposed to the jet even for very short treatment time, with the kINPen 09, operated in Ar, there was no significant difference between the quadrant exposed to the plasma jet and the remaining area. Finally, results for the DBD treatment are presented: since the DBD high voltage electrode was as large as the whole glass slide, treatment localization was obtained by employing as grounded counter electrode a metal layer (12x12 mm, a quarter of the glass slide) placed below one of the quadrants. As a result, plasma generation was limited to the area of the glass above the grounded counter electrode and only in this region a drastic WCA reduction was measured, while no significant variation was observed in the remaining quadrants. Results suggest the possibility to realize patterned modification of large surfaces using DBD sources with suitably shaped grounded counter.