Abstract
In aseptic loosening of endoprosthetic implants, metal particles, as well as their corrosion products, have been shown to elicit a biological response. Due to different metal alloy components, the response may vary depending on the nature of the released corrosion product. Our study aimed to compare the biological effects of different ions released from metal alloys. In order to mimic the corrosion products, different metal salts (CoCl2, NiCl2 and CrCl3 × 6H2O) were dissolved and allowed to equilibrate. Human osteoblasts were incubated with concentrations of 10 µM to 500 µM metal salt solutions under cell culture conditions, whereas untreated cells served as negative controls. Cells exposed to CoCr28Mo6 particles served as positive controls. The cell activity and expression of osteogenic differentiation and pro-osteolytic mediators were determined. Osteoblastic activity revealed concentration- and material-dependent influences. Collagen 1 synthesis was reduced after treatment with Co(2+) and Ni(2+). Additionally, exposure to these ions (500 µM) resulted in significantly reduced OPG protein synthesis, whereas RANKL as well as IL-6 and IL-8 secretion were increased. TLR4 mRNA was significantly induced by Co(2+) and CoCr28Mo6 particles. The results demonstrate the pro-osteolytic capacity of metal ions in osteoblasts. Compared to CoCr28Mo6 particles, the results indicated that metal ions intervene much earlier in inflammatory processes.
Highlights
The wear and corrosion of metal implant materials are the main risk factors for aseptic loosening and implant failure in orthopedic surgery
The results demonstrate the pro-osteolytic capacity of metal ions in osteoblasts
Since Toll-like receptor 4 (TLR 4) is known to be the most relevant receptor in aseptic implant loosening [30,37], we looked at TLR4 sensitization in human osteoblasts after exposure to metal salts and controls
Summary
The wear and corrosion of metal implant materials are the main risk factors for aseptic loosening and implant failure in orthopedic surgery. Metal surfaces are protected by a passive oxygen layer, electrochemical reactions are still present at the implant site [1]. Different components can cause galvanic effects resulting in oxidation and reduction reactions on the metal surfaces. Head-neck taper corrosion is the most prominent example of this in orthopedic surgery, especially for large-diameter metal-on-metal bearings [3], and for metal-polyethylene bearings [4]. Another type of corrosion is the intracellular reduction of wear particles in cells, especially in macrophages. When metal particles are taken up via active mechanisms or internalization, Materials 2019, 12, 2771; doi:10.3390/ma12172771 www.mdpi.com/journal/materials
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