UHMWPE oxidation increases granulocytes activation: a role in tissue response after prosthesis implant

Ultra-high molecular weight polyethylene (UHMWPE), a biopolymer widely used in orthopaedic implants, is oxidized during γ-ray sterilization; such surface oxidation is considered as major responsible for inflammation and prosthesis failure. As granulocytes are involved in first contact inflammation, we have measured their oxidative burst by flow cytometry using dihydrorhodamine 123 (DRH) to evaluate their activation following contact with normal and oxidized UHMWPE. Peripheral blood cells (obtained by lysed blood) were loaded with DRH, seeded onto polystyrene, normal and heat-oxidized UHMWPE disks for 30 min and then collected for analysis. Granulocytes were individuated using FSC and SSC signals and their cell associated green fluorescence was analyzed. Both normal and oxidized UHMWPE stimulated granulocytes activation as showed by the mean fluorescence emitted (109.3±3.8 and 150.1±9.2, respectively) compared to control samples (81.6±0.3). Moreover oxidized UHMWPE activated a significantly higher percentage of granulocytes (73.35±5.2%) compared to not-oxidized UHMWPE (21.5±3.8%). UHMWPE surface oxidation responsible for increased granulocyte activation seems to play a role in tissue response to implants.