Virgin gamma irradiated GUR-1050PE-UHMW and Vitamin E doped PE-UHMW samples were used. PE-UHMW was cut into small blocks of comparable geometry (m=85±2mg, V≈125mm3), which were either used for incubation experiments or sliced to 15 µm using cryostat (CM1950,Leica, Germany)and mounted on indium-tin oxide(ITO) coated glass slides (Sigma–Aldrich) using conductive tape (Shimadzu, Japan).The final polymer slice can exhibit folded regions after attachment. However, those regions were used to simulate uneven and rough regions and edges, as they actually occur in vivo, caused by mechanical wear and abrasion processes in the acetabular cup. All PE-UHMW samples were incubated in SF at 37 ◦C for 24 h. After incubation, samples were rinsed with uH2O and vacuum dried. For MS and MSI experiments standard MALDI matrices, α-cyano-4-hydroxycinnamic acid (HCCA) and sinapinic acid (SA) were dissolved in 70% acetonitrile (ACN),30% uH2O (v/v) containing 0.1% trifluoroacetic acid (TFA) at a concentration of 13 (HCCA) and 25 (SA) mg/mL. Automatic matrix deposition was performed using a chemical inkjet printer ChIP-1000 (Shimadzu) or a commonly used airbrush device (Conrad, Germany). For the airbrush application of MALDI matrix a working distance of 10–12 cm was chosen with an approximate angle of 50–60◦ covering the sample in several iterative steps.