Developing an in vitro Osteochondral Micro-Physiological System for Modeling Cartilage-Bone Crosstalk in Arthritis

Kyra Smith^1,2Stephanie L. Fung²Hsin-Fang Wu¹Irene Chiesa^3,4Giovanni Vozzi^3,4Carmelo De Maria^3,4Riccardo Gottardi^1,2,5*

• ¹University of Pennsylvania, Philadelphia, United States
• ²Children's Hospital of Philadelphia, Philadelphia, Pennsylvania, United States
• ³Research Center “E.Piaggio”, School of Engineering, University of Pisa, Pisa, Tuscany, Italy
• ⁴Department of Information Engineering, University of Pisa, Pisa, Tuscany, Italy
• ⁵Ri.MED Foundation, Palermo, Sicily, Italy

Arthritis, a disease affecting over 50 million adults in the United States, encompasses many different conditions involving joints and surrounding tissues. Disease development, progression, and subsequent treatment is dependent on many different factors, including the relationship between adjacent tissues and the immunological signals involved. A major contributor to disease regulation is the crosstalk between the cartilage and the bone in joints, as well as their reaction to immune factors such as cytokine signaling and macrophage mediation. Studying cartilage-bone crosstalk in arthritis development can be difficult, as controlling immunological factors in vivo is challenging, but in vitro models often lack multi-tissue relevancy. To fix this, we developeddevelop an in vitro microphysiological system using a biphasic bioreactor that supports modeling of multiple tissues. We generate cartilage and vascularized-bone analogs and combine them in the bioreactor to allow diffusion and signaling between them. Using this system, we can directly induce inflammation in the cartilage region and study how crosstalk between the two adjacent tissues contributes to disease progression. We show that conditioned media from pro-inflammatory macrophages generates a different inflammatory profile than a simple inflammatory cytokine cocktail. We also show that the vascularized-bone region becomes inflamed in response to the cartilage inflammation, verifying crosstalk in the system and successfully modeling the relationship between cartilage and bone in an arthritic environment. This model can be used to further probe the crosstalk between bone and cartilage in arthritis, allowing researchers to tease out the effect of specific inflammatory agents or therapeutics in vitro. 1 Introduction Arthritis is a group of complex diseases that affect bone and cartilage as well as the surrounding tissues in articular joints (Mankin et al., 2000;Ng and Azizudin, 2020). Arthritis is a major cause of