Cytotoxicity of control and NO releasing particles against L929 mouse fibroblast cells as measured using the MTS assay after (A) 2 h exposure at 0 (white), 0.4 (light grey), 0.8 (grey), 1.6 (dark grey), and 3.2 (black) mg mL−1 and after (B) 24 h exposure at 0 (white), 0.1 (light grey), 0.2 (grey), 0.4 (dark grey), and 0.8 (black) mg mL−1.