We are developing a X-ray based sensor inserted during surgery that could be used as a potential X-ray imaging functional chemical sensor for noninvasive detection and studying of hip implant infections. Hip surgeries are generally safe and effective procedures, however, about ~0.5-2% of prosthetic hips become infected. If these infections are not detected and treated promptly, the implant must be removed, followed by reinsertion of the medical device after the infection is eradicated. The sensor developed measures synovial fluid pH which decreases from pH 7.5 to around pH 6.7 during hip infection. The sensor employs a pH-responsive polyacrylic acid-based hydrogel which swells at high pH and shrinks at low pH, thereby moving a radiodense tantalum bead embedded in the hydrogel. Plain radiographs of the sensor in synovial fluid (pH ranging from 6.5-7.5) clearly showed the movement of the tantalum bead relative to a tungsten wire marking the position at pH 7. The sensor has a linear and repeatable response within 30 minutes in the range of pH 6.5 and 7.5 in bovine synovial fluid solutions and a pH accuracy of 0.08 pH units. An interobserver study of a randomized series of radiographs of sensor demonstrated an interobserver precision of 0.03 pH units. In future, the sensor will be tested in a sheep model to test the sensor performance in vivo.

Identification of hip infections by a X-ray based synovial fluid pH sensor

ACS Fall 2021

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