Improved cell adhesion to ion beam-irradiated polymer surfaces.

A very strong improvement of the cell adhesion, spreading and proliferation was observed for ion beam irradiated surfaces of polyethersulphones and polyurethane. The improvement shows a characteristic ion fluence-dependence with a threshold around 1 x 10(15) ions cm-2. We have compared this improvement of surface cytocompatibility with the various ion-induced chemical and physical modifications of the polymeric surfaces, taking into account their characteristic fluence-dependence. The irradiation induced a severe compositional and chemical modification of the polymeric surfaces as detected by X-ray photoelectron spectroscopy. Contact angle measurements showed that the surface free energy was strongly modified by ion irradiation. The fluence-dependent formation of a hydrogenated amorphous carbon phase was demonstrated by Raman spectroscopy. Our findings indicate that neither the simple modification of the functional groups nor the mere elemental composition nor the modification of the surface free energy can explain the observed fluence-dependence of the cell adhesion enhancement. On the contrary, we show that this enhancement correlates with the formation of a highly specific ion-induced 'unsaturated' a-C:H phase. According to these findings, we suggest that the formation of a substantial amount of hydrogenated amorphous carbon phases is the major factor promoting the cytocompatibility of ion irradiated polymer surfaces.