IL-1β expression in THP-1 cells. Blue bars: uncoated particles. Purple bars: particles with TEOS-mercaptosilane coating. THP-1 cells were stimulated for 18 h with coated or uncoated particles at 1:1 stoichiometry of particles to cells and then assayed for IL-1β activity. PBS, phosphate-buffered saline solution; PS, polystyrene particles; PS coat, TEOS-mercaptosilane-coated PS particles; PLGA, poly(lactic coglycolic acid) particles; PLGA coat, TEOS-mercaptosilane coated PLGA particles; PMMA, poly(methyl methacrylate) particles; PMMA coat, TEOS-mercaptosilane coated PMMA particles; PE, polyethylene particles; PE coat, TEOS-mercaptosilane coated PE particles. *p < 0.05, **p < 0.01.