The role of mechanobiology in bone and cartilage model systems in characterizing initiation and progression of osteoarthritis.

Multifaceted changes in the mechanobiological environment of skeletal joints, at multiple length scales, are central to the development of diseases-like osteoarthritis (OA). Recent evidence demonstrates related mechanical alterations in both bone and cartilage tissues, with crosstalk between the tissues being an important factor in acute and chronic degenerative processes. However, recapitulating multicellular tissue systems in the laboratory to study the entire osteochondral unit remains challenging. Thus, the development of accurate and reproducible OA model systems and the selection of the most suitable model for individual experimental approaches are critical. This review first discusses recent progress in understanding mechanosensory processes in healthy and osteoarthritic joints. Subsequently, we review advancements in the development of and model systems ranging from 2D monocultures through to joint organ-on-a-chip models. Use of these systems allows for the study of multiple cell types in controlled, reproducible, and dynamic environments, which can incorporate precisely controlled mechanical and biochemical stimuli, and biophysical cues. The way in which these models have, and will continue to, improve our ability to recapitulate complex mechanical/paracrine signaling pathways in osteochondral tissues is then discussed. As the accuracy of model systems advances, they will have a significant impact on both our understanding of the pathobiology of OA and in identifying and screening therapeutic targets to improve treatment of this complex disease.