Cellular responses to radical propagation from ion-implanted plasma polymer surfaces

Biomolecule-functionalization, through the presentation of biological motifs that promote optimal cellular responses, has the capacity to improve the tissue integration of biomedical devices and hence patients' quality of life. Radical-functionalized plasma polymer films (rPPFs) readily immobilize bioactive molecules on exposure to a biomolecule-containing aqueous solution without the need for chemical reagents. However, the potential for damage to cells and tissues due to the high local concentration of radicals in freshly deposited radical-functionalized plasma polymer films is of concern. In this study, we compared a fresh (4 h post-deposition) rPPF with one that had been aged for 11 days to explore the effect of the different radical fluxes on cellular responses. Primary osteoblasts and MG63 bone osteosarcoma cells were used to determine whether rPPFs at early aging times exhibited radical-induced cytotoxicity. The aging behavior of the rPPFs demonstrated a connection between the radical decay kinetics and the surface chemistry and wettability. Significant increases in cell attachment and spreading compared to bare Ti were observed for both cell lineages on the rPPF surfaces. The proliferation assays showed equivalent proliferation rates on both the fresh and aged surfaces, and no evidence of cytotoxicity was observed. Overall, we demonstrated that the high flux of radicals emerging to the surface has minimal influence on the biocompatibility of radical-functionalized plasma polymer films.