Figure 2. Injected PMMA beads undergo fibrotic encapsulation and vascularisation that resembles the chronic phase of the foreign body response.

PMMA bead aggregates from wild-type B6 mice at (a) day 7 or (b) day 14 were sectioned at 5 μm and stained with Masson’s Trichrome for the detection of pan collagen which is stained blue, and nuclei stained dark purple. (c) At day 7 and (d) day 14 red blood cells that stained red were observed in the blood vessels (black arrows) that had formed within the bead aggregates. (d) We also observed encapsulation of individual beads by collagen (stained blue) as highlighted by the white arrows. PMMA bead aggregates were sectioned at 5 μm for immunohistochemistry staining of (e) collagen I and (f) collagen II as observed by brown staining. Scale bar, 250 μm. The presence of collagen II was detected by 48 h, which is observed as light brown staining and indicated by the black arrows (80x magnification; scale bar, 25 μm). Representative images are shown of the 4–8 mice per group per time point.