– Lipidoid S14 is a novel lipidoid for siRNA delivery.Lipidoid-polymer hybrid nanoparticle (FS14-NP) can efficiently deliver siRNA against IL-1? (siIL-1?) to macrophages and effectively suppress the pathogenesis of experimental arthritis induced by collagen antibody (CAIA mice). FS14-NP/siIL-1? achieved approximately 70% and 90% gene-silencing efficiency in the RAW 264.7 cell line and intraperitoneal macrophages, respectively. Intravenous administration of FS14-NP/siRNA led to rapid accumulation of siRNA in macrophages within the arthritic joints. Furthermore, FS14-NP/siIL-1? treatment lowered the expression of pro-inflammatory cytokines in arthritic joints and dramatically attenuated ankle swelling, bone erosion, and cartilage destruction.