Developing a cartilage-on-chip platform for osteoarthritis

Osteoarthritis (OA) is a progressive degenerative joint disease that impacts millions of individuals globally. Despite extensive research efforts to understand the disease and develop effective therapies, current treatments remain limited to surgery and palliative medication. The lack of robust preclinical models for OA poses a significant challenge to advancing research on disease-modifying osteoarthritis drugs (DMOADs). Consequently, there is a need for in vitro models that can accurately assess the DMOADs.

Injectable hybrid hydrogels comprising tyramine (TA)-functionalized hyaluronic acid (HA), dextran (Dex), and chondroitin sulfate (CS) that crosslink in situ upon mixing with horseradish peroxidase and H2O2 have been developed and demonstrated to enhance the chondrogenic activity of human articular chondrocytes (ACs) and nasal chondrocytes (NCs) in free-swelling scaffolds. In this study, we investigated the chondrogenic activity of chondrocytes-laden hydrogels at the microscale using the RE-PLATE multi-compression Cartilage-on-Chip (CoC) platform provided by Chiron B.V. By leveraging the platform's capability to apply mechanical compression, we were able to compare chondrogenesis under static and actuated conditions among different hydrogel formulations.

Hybrid hydrogels comprising Dex-TA, HA-TA, and CS-TA laden with healthy ACs or NCs were tested. Encapsulated cells were cultured in a chondrogenic medium for 21 days in either static condition or subjected to mechanical stimulation for 1 hour every day under physiological loading (400 mBar, 1 Hz). Chondrogenic activity was assessed by RNA expression and immuno-staining of the hydrogels. Cell viability and cell migration were also observed during the culture period.

Loading of the CoC with the cell-laden injectable hydrogels was easy and resulted in complete filling of the respective cell/hydrogel compartment. All hydrogel formulations remained structurally intact and maintained high cell viability after 21 days under static and mechanical stimulation. Cell migration was observed under actuated conditions, suggesting an early cellular response to mechanical stimulation, as cells tended to move closer to the stimulation source. Enhanced up-regulation of cartilage-associated genes such as ACAN, COLII, and SOX9, was observed for all mechanically actuated hydrogel formulations. Correspondingly, the immuno-staining showed higher deposition of COLII and proteoglycans in actuated conditions.

The hybrid hydrogel system, incorporating Dex-TA, HA-TA, and CS-TA, successfully served as a scaffold supporting cell proliferation and chondrogenic differentiation within the CoC platform. Mechanical stimulation enhanced chondrogenic activity in ACs and NCs, highlighting the platform's potential for mimicking healthy cartilage tissue. This easy-to-use innovative CoC platform has great potential for application in the screening of DMOADs.