The role of lubrication in function and degeneration of articular cartilage: a critical review and perspectives

Articular cartilage is a porous, soft tissue present in the synovial joints that distributes the load and lubricates the joint for smooth body movements. Arthritis or joint diseases lead to cartilage degeneration. However, the triggering factors of these joint diseases are still debated, with uncertainties about the key mechanisms and the mechanochemical and biological interactions that make this a very complex interdisciplinary problem. Nonetheless, mechanical stresses and improper lubrication are widely accepted as important contributors to cartilage degeneration. This review paper focuses on the friction, lubrication, and biomechanical aspects that affect cartilage function and are, therefore, linked to its degeneration. Further, lubrication theories related to cartilage that have been proposed to study ultra-low friction of cartilage will be discussed. Over the past decade, there has been significant advancement in understanding cartilage rehydration and how different activities keep cartilage lubricated; these will be reviewed together with the advances in experimental and modeling techniques that have enabled recent breakthroughs in our understanding. The need for new and improved methodologies in experimental and modeling work to deepen our understanding of cartilage biomechanics across the scales, as well as its evolution and degeneration will be discussed. Finally, with the widespread use of artificial intelligence (AI) and machine learning (ML) in scientific research, this paper explores the avenues in which AI and ML can contribute to enhancing the ongoing research on cartilage.