Synovium‐On‐A‐Chip: Simulating the Microenvironment of the Rheumatoid Arthritis Synovium via Multicell Interactions to Target Fibroblast‐Like Synoviocytes

Fibroblast-like synoviocytes (FLSs) play pivotal roles in the synovial inflammation of rheumatoid arthritis (RA) and are promising therapeutic targets. Currently, few in vitro models effectively mimic the characteristics of RA FLSs. In this study, microfluidic chips, 3D culture systems, and flow-based culture techniques are integrated to develop a vascularized and immune-activated synovium-on-a-chip (SOC) model. Using immunofluorescence staining, multiparametric flow cytometry, and ELISA, the optimal coculture ratio of RA FLSs, M1-type macrophages, and human umbilical vein endothelial cells is determined to be 1:1:1 (2 × 10⁶ cells/mL). Analyses of inflammatory cytokine profiles from 22 blood samples, 48 synovial fluid samples, and six synovial tissues demonstrate that the SOC model consistently maintains elevated levels of interleukin (IL)-6 and IL-8 over 9 days, closely recapitulating RA synovial inflammation. Additionally, RA FLSs in the SOC model exhibit elevated levels of Cadherin-11, matrix metalloproteinase (MMP)-1, MMP-3, and Ki-67. By evaluating the therapeutic efficacy and toxicity of triptolide and celastrol, this study confirms the potential of the SOC model in predicting in vivo drug responses, thereby offering a promising tool for preclinical drug assessment in RA-related research.