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 atatmospheric pressure in both air and an ammonia/nitrogen gas mixture have been analysed usingwater contactangle, XPS and AFM. The water contact angle for cellulose processed in air decreased significantly after exposureto DBD. XPS indicated that changes in surface chemistry are not the main cause of this reduction in wettability.AFMstudies clearly show that a significant increase in surface roughness results fromthe plasma treatment andthat there is a correlation between the increased Ra/Rq values for higher applied power and processing cyclenumbers and the associated changes observed in the water contact angles. When cellulose is plasma processedin a v/v 10%NH3/90%N2 gasmixture the surface undergoes functionalisation with nitrogen groups as indicated byXPS analysis. Specifically, the formation of both amine (NH2) and to a lesser extent amide (CONH2)moietiesis evident. The contact angle results for these samples indicate an initial decrease in wettability followed by relaxationto slightly higher values consistent with a degree of surface relaxation post-processing. The correspondingAFM data indicate that whereas the slight increase in surface roughness contributes to the change inhydrophilicity, unlike processing in air, it is not the only factor involved. In this case, it is the modified surfacechemistry that has the greatest influence for cellulose processed under these conditions. Hence, despite its inherentlyhigh oxygen content, cellulose can bemodified using atmospheric plasma in air and 10%NH3/90%N2 to producemodified surface properties known to actively promote biological cell adhesion. This offers a route toenhance the role that this abundant biomaterial can play as a construct for tissue engineering and relatedapplications.