Protein adhesion and cell response on atmospheric pressure dielectric barrier discharge-modified polymer surfaces

Gaseous plasma discharges are one of the most common means to modify the surface of a polymer without affecting its bulk properties. However, this normally requires the materials to be processed in vacuo to create the active species required to permanently modify the surface chemistry. The ability to invoke such changes under normal ambient conditions in a cost-effective manner has much to offer to enhance the response of medical implants in vivo. It is therefore important to accurately determine the nature and scale of the effects derived from this technology. This paper reports on the modification of poly(styrene) (PS) and poly(methyl methacrylate) (PMMA) using atmospheric pressure plasma processing via exposure to a dielectric barrier discharge (DBD). The changes in surface chemistry and topography after DBD treatment were characterised using water contact angle, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy. A marked increase in the surface oxygen concentration was observed for both PMMA and PS. An increase in surface roughness was observed for PMMA, but not for PS. These changes were found to result in an increase in surface wettability for both polymers. Adsorption of albumin (Alb) onto these substrates was studied using XPS and quartz crystal microbalance with dissipation (QCM-D). The rate of adsorption of Alb onto pristine PMMA and PS was faster than that on the DBD-treated polymers. XPS indicated that a similar concentration of Alb occurred on both of the treated surfaces. Deconvolution of the C1s XPS spectra showed that Alb is adsorbed differently on pristine (hydrophobic) compared to DBD-treated (hydrophilic) surfaces, with more polar functional groups oriented towards the upper surface in the latter case. The QCM-D data corroborates this finding, in that a more viscoelastic layer of Alb was formed on the DBD-treated surfaces relative to that on the pristine surfaces. It was also found that Alb was more easily replaced by larger proteins from foetal bovine serum on the DBD-treated surfaces. The viability of human lens epithelial cells on both of the DBD-treated polymer surface was significantly (P<0.05) greater than on the respective pristine surfaces. In addition, cells that adhered to the treated polymers exhibited a polygonal morphology with well spread actin stress fibres compared with the contracted shape displayed on the pristine surfaces. The results presented here clearly indicate that DBD surface modification has the capability to influence key protein and cell responses.