Surface modification of cellulose via atmospheric pressure plasma processing in air and ammonia-nitrogen gas

Changes to the surface properties of cellulose induced by a dielectric barrier discharge (DBD) plasma operating at atmospheric pressure in both air and an ammonia/nitrogen gas mixture have been analysed using water contact angle, XPS and AFM. The water contact angle for cellulose processed in air decreased significantly after exposure to DBD. XPS indicated that changes in surface chemistry are not the main cause of this reduction in wettability. AFM studies clearly show that a significant increase in surface roughness results from the plasma treatment and that there is a correlation between the increased Ra/Rq values for higher applied power and processing cycle numbers and the associated changes observed in the water contact angles. When cellulose is plasma processed in a v/v 10%NH3/90%N-2 gas mixture the surface undergoes functionalisation with nitrogen groups as indicated by XPS analysis. Specifically, the formation of both amine (-NH2) and to a lesser extent amide (-CONH2) moieties is evident. The contact angle results for these samples indicate an initial decrease in wettability followed by relaxation to slightly higher values consistent with a degree of surface relaxation post-processing. The corresponding AFM data indicate that whereas the slight increase in surface roughness contributes to the change in hydrophilicity, unlike processing in air, it is not the only factor involved. In this case, it is the modified surface chemistry that has the greatest influence for cellulose processed under these conditions. Hence, despite its inherently high oxygen content, cellulose can be modified using atmospheric plasma in air and 10%NH3/90%N-2 to produce modified surface properties known to actively promote biological cell adhesion. This offers a route to enhance the role that this abundant biomaterial can play as a construct for tissue engineering and related applications. (C) 2013 Elsevier B.V. All rights reserved.