Synovial Fluid pH Sensor for Early Detection of Prosthetic Hip Infections

Abstract

An implantable sensor developed to measure synovial fluid pH for noninvasive early detection and monitoring of hip infections using standard‐of‐care plain radiography is described. The sensor is made of a pH responsive polyacrylic acid‐based hydrogel, which expands at high pH and contracts at low pH. A radiodense tantalum bead and a tungsten wire are embedded in the two ends of the hydrogel to monitor the change in length of the hydrogel sensor in response to pH via plain radiography. The effective acid dissociation constant (pKa) of the hydrogel‐based pH sensor is 5.6 with a sensitivity of 3 mm/pH unit between pH 4 and 8. The sensor shows a linear response and reversibility in the physiologically relevant pH range of pH 6.5 and 7.5 in both buffer and bovine synovial fluid solutions with a 30‐minute time constant. The sensor is attached to an explanted prosthetic hip, and the pH response is determined from the X‐ray images by measuring the length between the tantalum bead and the radiopaque wire. Therefore, the developed sensor will enable noninvasive detection and studying of implant hip infection using plain radiography.

Multimodal Hydrogel‐Based Respiratory Monitoring System for Diagnosing Obstructive Sleep Apnea Syndrome

“…Wearable electronics have aroused great attention in personal healthcare, artificial intelligence, and electronical skins, [8][9][10][11][12] which greatly promote the development of portable and flexible sensors for monitoring individual health. Electronical sensors could transform the mechanical, [13][14][15][16][17][18][19] thermal, [20][21][22][23][24] humidity, [2,[25][26] or other stimulus [27][28] to visual electronic signals that could be monitored in situ. A great amount of efforts have been devoted to monitoring respiratory related signals through pressure, temperature, or humidity from nostril airflow, [1,20,25,[29][30] as well as the up-and-down movement of chest or abdomen, [15,16,[31][32][33] including the heart rate or arterial pulse.…”

Recent progress in conductive self‐healing hydrogels for flexible sensors

“… 130 Besides, hydrogel sensors have been developed in a variety of applications in vivo . For example, Anker's group 134 developed hydrogel‐based pH sensor to measure synovial fluid pH for noninvasive early detection and monitoring of hip infections. Strano's group 135 developed a nanoparticle hydrogel sensor for the recognition of cortisol, progesterone, and steroids, which would be employed for the dynamic measurement of steroid hormones in vivo .…”

pH variation in medical implant biofilms: Causes, measurements, and its implications for antibiotic resistance

“…(O) Schematic of the prosthetic hip implant with attached pH sensor. Inset shows the mechanism of pH sensing ( Wijayaratna et al, 2021 ). (P) X-ray images of pH sensor at pH 6.5 and 7.5 in bovine synovial fluid ( Wijayaratna et al, 2021 ).…”

“…These figures were reproduced with permission from Hu et al (2013) , Shaibani et al (2016) , Wang et al (2013) , Wang et al (2015) , Florence and Attwood (2007) , and Wijayaratna et al (2021) .…”

“…Both these sensors enabled noninvasive mapping of local pH, with high spectral resolution ( Wang et al, 2015 ; Uzair et al, 2019 , 2020 ). A hydrogel sensor that can be attached to a prosthetic hip implant is able to measure synovial fluid pH using plain radiography ( Wijayaratna et al, 2021 ). The sensor consists of a pH-responsive hydrogel with a radiodense tantalum bead and a metal wire at the two ends.…”