The density of TRAIL on the surface of PDMV-coated particles was varied at 0, 0.2, 0.5, and 1 μg TRAIL/mg Si particles. (a) TRAIL was immunostained by FITC-anti human TRAIL. PDMV-coated particles with TRAIL conjugation of varied density were incubated with breast cancer cells MDA-MB-231 and prostate cancer cells PC3 at particle-to-cell ratios of 1:1, 2:1, 5:1, and 10:1 for 24 hr. Cell viability was measured by MTT assay. (b) TRAIL conjugation on PMDV-coated Si particles was nontoxic to endothelial cells. PMDV Si particles at a conjugation density of 0 or 1 μg TRAIL/mg Si particles were incubated with HUVECs with different particle-to-cell ratios. Cell viability in each treatment group was normalized to the treatment with 0 μg TRAIL/mg Si particles at 1:1 particle-to-cell ratio. (c) Comparing efficacy of soluble TRAIL versus TRAIL immobilized to PDMV-coated Si particles in inhibition of cancer cell proliferation. PMDV-coated Si particles (1 μg TRAIL/mg silica coating density) were incubated with cancer cells at different particle-to-cell ratios and compared to soluble TRAIL at a concentration matched to respective particle-to-cell ratios. (d) TRAIL conjugation did not interfere with the ability of PDMA-coated Si particles to adhere to a fibrin-immobilized surface under flow. All results are presented as the mean ± SEM, n=3; ns indicates no significant difference.