Abstract In this study, a reactive oxygen species (ROS)‐responsive hydrogel sensor (PD/MnO 2 hydrogel) is developed that can efficiently detect senescent cells. Using immature murine articular chondrocytes with serial passages, the sensor can identify small interfering RNA (siRNA) knockdown of peroxisome proliferator‐activated receptor‐alpha (PPARα) based on the concentration of ROS in cells, simultaneously maintaining its balance via scavenging activity to prevent cartilage degradation in osteoarthritis (OA). The hydrogel sensor exhibits a change in electronic properties, with a distinct resistance from 201.9 kΩ for P0 to 362.9 kΩ for P3, and fluorescence off/on performance with an increase in passaging time. In vitro investigation using PPARα‐specific siRNA reveals a correlation between pressure sensitivity and senescent activity, wherein an elevation in observed signal occurred (41.5%). In vivo analysis reveals significant decrease in degradation of the cartilage of both young, 3 months old aged, 18 months old, and PPAR α −/− mice compared to PPAR α +/+ mice based on safranin O stains. The expression level of interleukin‐1β is reduced in the cartilage of aged PPAR α −/− mice after implantation with hydrogel, indicating the potential of PD/MnO 2 hydrogel as a therapeutic modality against OA.