The exact mechanism of cartilage breakdown in osteoarthritis is unknown, but damage from mechanical stress with insufficient self-repair is believed to be the main culprit. The composition of synovial fluid, or joint lubricant, changes significantly: The concentration and molecular weight of hyaluronic acid tends to decrease. In Biointerphases, researchers explore the disease-driven breakdown of hyaluronan and the mechanistic implications of these changes on the lubrication and subsequent wear of joints.