Biomechanically Loaded 3d Tissue-Mimetic Lab-on-a-Chip Models for Human Inflammation and Fibrosis Modelling

Joint tissue homeostasis relies on biomechanical signals and biochemical cues, with gait-related biomechanical forces significantly influencing knee joint health. Physiological loading promotes anti-inflammatory responses, protecting tissue homeostasis, while excessive loading exacerbates inflammation and accelerates knee osteoarthritis (OA) progression. Lab-on-a-chip technology enables investigation of biomechanical and biochemical interactions in biomimetic cartilage, synovial tissue, tendon, and ligament models. Primary synovial-like fibroblasts and articular chondrocytes from OA and non-OA human and equine patients were encapsulated in TISSEEL fibrin hydrogel to create biochip models. Cartilage and synovial tissue cultures were exposed to cyclic flow perfusion (1 Hz, 1 week) with or without pro-inflammatory triggers (10 ng/mL TNF-α and IL-1β). Tendon and ligament models were formed by embedding ligamentocytes in Collagen I hydrogel, matured for 7 days, and subjected to uniaxial strain (29% at 0.25–0.5 Hz for 4 hours) in similar inflammatory conditions. Gene expression analysis of physiological markers (e.g., COL1A1, COL2A1, ACAN) and OA-related pro-inflammatory cytokines (IL6, CXCL8) and matrix metalloproteases (MMP1, MMP3, MMP13) was performed. Cartilage mono-cultures derived from non-OA equine cells exhibited increased inflammatory responses (e.g., IL6, MMPs) under cyclic flow perfusion, while synovial mono-cultures showed anti-inflammatory and anti-fibrotic effects (reduced IL6 and MMP1). Interestingly, combined biochemical stimulation and perfusion in synovial and cartilage monocultures demonstrated an anti-inflammatory effect. However, cartilage-synovium co-cultures retained a stronger pro-inflammatory response compared to mono-cultures. For ligament models, cyclic mechanical straining in a pro-inflammatory environment amplified IL6 and MMP1 expression (p < 0.05). Notably, ligament models derived from high-passage cells exhibited diminished mechano-sensitivity, showing no response to biomechanical loading. These findings suggest that prolonged cell culture may impair ligamentocytes' mechanical responsiveness. Although traditionally considered a cartilage-centric disease, OA involves complex interactions among multiple joint tissues. Advanced lab-on-a-chip platforms, leveraging patient-derived cells, recreate these interactions, providing critical insights into early OA pathogenesis and the contributions of bystander tissues.