Localized Oxygen Control in a Microfluidic Osteochondral Interface Model Recapitulates Bone–Cartilage Crosstalk During Osteoarthritis

Abstract Osteoarthritis (OA) is characterized by the dysregulation of the osteochondral interface between bone and cartilage. In vitro, osteochondral models are crucial for studying OA and testing treatments. However, current models are limited to replicating the extracellular matrix's structural and mechanical heterogeneity and do not account for the distinct oxygen gradients that chondrocytes and osteoblasts experience at the osteochondral interface. By using micropatterned granular hydrogels to control oxygen scavenging agents' delivery, maintaining <1% oxygen concentration in standard cell culture conditions. These hypoxic hydrogels allow primary human chondrocytes to exhibit a more anabolic phenotype, akin to hypoxic incubator conditions. Patterning of the hydrogels in a microfluidic device creates localized hypoxic environments that mimic the osteochondral interface, enabling co‐culture of chondrocytes with osteoblasts from non‐sclerotic and sclerotic subchondral bone. This co‐culture in differential oxygen conditions revealed that sclerotic osteoblasts induce collagen expression changes in chondrocytes through MMP13 and ADAM15 production, a phenomenon not observed in uniform oxygen environments. Additionally, this model uncovered extensive transcriptional changes involving NF‐κβ, TGF‐β/BMP, and IGF signaling pathways, induced by sclerotic osteoblasts, which are undetectable in normoxic co‐cultures. The microfluidic model with localized oxygen variations effectively simulates osteoblast‐chondrocyte interactions, offering significant insights into OA pathophysiology.