Cellular attachment to ultraviolet ozone modified polystyrene surfaces

The surfaces of standard untreated polystyrene cell culture dishes have bee n oxidatively modified for up to 8 min exposure time using an ultraviolet o zone treater in order to promote cell adhesion. Surface oxygen chemisorptio n and topographical modification has been characterized using monochromatic X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM), respectively. The oxidation process is shown to proceed at low exposure tim es (<60 s) via the formation of C-OR groups, although some R2C=O and RO-C=O groups are also formed. At longer treatments, RO-C=O groups become the dom inant species, although the other groups are also present. The maximum leve l of oxygen reached is 36 atomic 8. Some of the oxygen present at surfaces treated at times of >60 s is in the form of loosely bound low molecular wei ght oxidized material (LMWOM) which is produced by oxidative scission of th e PS backbone. Water washing leads to a reduction in surface oxygen content mainly by the removal of RO-C=O and R2C=O functional groups. The residual stable oxygen levels, which can be introduced, are approximately 20-25 atom ic %. Surface chemistry changes are accompanied by the formation of surface spikes which are about 30 nm high and 300-400 nm wide. A correlation betwe en treatment time/oxygen level and overall roughness is observed. The effec t of washing upon the topography is to slightly increase the surface roughn ess, although not to a significant degree. The attachment kinetics of adhes ion for Chinese hamster ovary cells show that adhesion occurs much more rap idly for oxidized surfaces than for untreated control materials. A direct c orrelation between the levels of oxidation and the rate of cell adhesion is demonstrated.