Fig. (1) Osteoclast maturation and particle challenge: Light microscopy was used to image monocytes/macrophages and osteoclasts. Peripheral blood mononuclear cells (PBMCs) are obtained from human whole blood, and monocytes/macrophages are isolated from the PBMCs and plated in 96-well plates. (A) Freshly isolated monocytes/macrophages at day 1, (B) Large osteoclast-like cells (some likely multinucleated, arrows) formed at day 6-7 after 100 ng/ml RANKL and 50ng/ml M-CSF treatment, (C) Monocytes/macrophage with Co-alloy particles at 8 hours post-challenge, (D) Osteoclast-like cells 24 hours post challenge with Co-alloy particles showing phagocytosis, (E) Non-TRAP positive monocytes/macrophages, (F) TRAP-positive stained osteoclast-like cells (i.e. post RANKL/M-CSF stimulation), (Note: Bar = approx 50 microns, original mag A: 200x, B-F: 600x).