An Interface‐Adapted Fiber Sensor for Real‐Time Monitoring of Biochemical Markers in Synovial Fluid

Abstract Osteoarthritis is a chronic, degenerative, and disabling disease affecting over 500 million people worldwide, leading to significant medical costs. Monitoring changes in the biochemical components of synovial fluid is crucial for understanding the onset and progression of osteoarthritis. However, this remains a challenge because the volume of synovial fluid is low, synovial tissue is prone to inflammation after mechanical injury, joint movement is frequent, and the space is limited, which poses significant limitations for the sensor‐tissue interface and the size of the device. Here, an interface‐adapted fiber sensor is developed that is minimally invasive of the joint cavity. The sensor obtains detection results comparable to the clinical gold standard (accuracy > 96.8%) and does not induce additional joint inflammation. Animal behavioral tests also confirm that sensor implantation does not interfere with normal movements in rats. When applied to an osteoarthritis model, the sensor enables real‐time monitoring of asymmetric dimethylarginine and lactate levels in the synovial fluid, providing insights into cartilage cell damage and glycolysis abnormalities at different stages of the disease. This new approach offers an effective tool for real‐time monitoring and early diagnosis of osteoarthritis.