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

Osteoarthritis (OA) often begins with dysregulation at the osteochondral interface between bone and cartilage. Understanding OA pathophysiology and testing treatments require in vitro osteochondral models. While current models can replicate the extracellular matrix's structural and mechanical heterogeneity, they are inadequate to create differential oxygen gradients affecting chondrocytes and osteoblasts. We used micropatterned granular hydrogels to control oxygen concentration without hypoxic incubators. These hydrogels enabled primary human chondrocytes to exhibit an anabolic phenotype similar to hypoxic incubator conditions. Patterning hydrogels in microfluidic devices created localized hypoxic environments mimicking the osteochondral interface, allowing co-culture of chondrocytes and osteoblasts from non-sclerotic and sclerotic subchondral bone. Our co-culture in differential oxygen conditions showed that sclerotic osteoblasts induce collagen expression changes in chondrocytes via MMP13 and ADAM15 production, a phenomenon absent in uniform oxygen environments. This model revealed extensive transcriptional changes involving NF-κβ, TGF-β/BMP, and IGF signaling pathways induced by sclerotic osteoblasts, undetectable in normoxic co-cultures. This microfluidic model with localized oxygen variations effectively simulates osteoblast-chondrocyte interactions, providing significant insights into OA pathophysiology.