gms | German Medical Science

Objectives: Total joint replacement is highly successful but CoCrMo-alloys can undergo tribocorrosion causing adverse local tissue reactions in periprosthetic tissue endangering long-term survival rates. Likely, degradation products are initially highly bioreactive and become electrochemically stable over time. Further, bio-reactiveness is typically judged in monolayer cell culture, not reflecting the complex interaction of different cell types in their 3D environment. The aim of this study was the development a bio-tribological testing system to produce/challenge (a) a macrophage cell line and (b) human synovium with freshly in situ produced and, thus, dynamically bioactive degradation products.

Methods: Wear production: ball-on-disc unit (Al₂O₃-on-CoCrMo), 37 N (>50 MPa) contact load, 20-40° amplitude, 2 Hz frequency combined with three-electrode configuration for potential control to force the ion release (Figure 1 [Fig. 1]). Metal release quantified by weight loss and by measurement of wear scar volume via white light interferometry. Cell culture: Human THP-1 macrophages exposed to metal degradation products under different electrochemical potentials to force a metal dissolution. Cell viability quantified via luminescent cell viability assay (CellTiter-Glo® 2.0). Human synovium: Human synovial membranes (f, 70 yrs., Gift of Hope, Itasca, IL, IRB exempt) split into halves, each half assigned to internal control or test group. Exposure of test group to +0.9 V electrochemical potential combined with wear production. Tissue reaction evaluated by macroscopic appearance and cell viability using a fluorescent live/dead assay.

Results and conclusion: Macrophages: metal degradation products showed dose dependent decrease of cell viability compared to the control group: 53%: -0.9V current control, p=0.0009; 24%: 0V + wear, p<0.0001; 13%: positive control Nigericin, p<0.0001, <1%: + 0.9V high metal ion release, p< 0.0001. Human synovium: macroscopic scale: gray-black tissue discoloration. Cell viability: 20±4% reduction compared with control (>95%) (p=0.03) (Table 1 [Tab. 1]). The present findings confirm that the newly invented bio-tribometer is producing a sufficient amount of biological active degradation products to challenge cells within a monolayer culture or within their native 3D matrix. Further investigations will focus on dose-response correlations and on extending the methods of measuring the cytotoxic and inflammatory effects of metal degradation products.