X‐Ray Visualized Synovial Fluid Carbon Dioxide Sensor for Early Detection of Prosthetic Hip Infections

Abstract

A radiographically visualized implantable dissolved carbon dioxide (CO2) sensor is developed to non‐invasively detect and monitor hip infections. The sensor is based on a pH‐responsive hydrogel as the sensing material, immersed in a carbonate buffer contained in a capsule with a CO2‐permeable membrane. Dissolved CO2 decreases the buffer pH causing the polyacrylic acid‐based hydrogel to shrink. The hydrogel length is determined using plain radiography by measuring the movement of a radiodense tantalum bead embedded in the hydrogel with respect to a metal wire in the casing. The sensor shows a clear response in the range of 15–115 mm Hg CO2, with a 4.3 mm Hg precision at 15 mm Hg CO2 level and a 6.4‐hour response time. The hydrophobic CO2‐permeable membrane is impermeable to aqueous molecules rendering the CO2 measurement independent of the external solution pH, which can be measured with a separate X‐ray visualized sensor. Separating the sensor from the aqueous environment is also expected to reduce the potential for biofouling and increase longevity. In summary, the first dissolved gas sensor that can be visualized radiographically is described; it has potential applications in detecting and studying implant infection and local carbon tissue CO2 levels.