Preliminary study on the effects of ageing cold oxygen plasma treated PET/PP with respect to protein adsorption

Surfaces of polyethylene terephthalate (PET) and polypropylene (PP) have been modified by oxygen plasma. The surface hydrophilicity and changes in topography during up to 90 days storage in water and in dry air in a desiccator were analysed by dynamic contact angle test and atomic force microscopy (AFM). Clear ageing effects on the plasma treated surface were observed as increases in contact angle and changes in roughness as functions of increasing storage time. However, the effect of oxygen plasma treatment to increase the hydrophilicity of surface was still evident on the treated surfaces even after 90 days storage either in dry air or in water. In protein adsorption experiments, human serum albumin (HSA) and fibrinogen (Fg) were adsorbed on untreated and oxygen plasma treated PET and PP surfaces. The quantified ATR–FTIR results showed that both HSA and Fg adsorption on PET and PP surfaces decreased after oxygen plasma treatment, with the effect most evident for HSA. Although for both proteins adsorption increased with ageing, the amount of adsorbed proteins was still lower than untreated surface at 30 days. This suggests the shelf life of oxygen plasma treated samples could be as long as 30 days.