An implanted pH sensor read using radiography

Arifuzzaman, Md; Millhouse, Paul W.; Raval, Yash S.; Pace, Thomas B.; Behrend, Caleb; Behbahani, Shayesteh Beladi; DesJardins, John D.; Tzeng, Tzuen‐Rong; Anker, Jeffrey N.

doi:10.1039/c8an02337a

Cited by 21 publications

(25 citation statements)

References 44 publications

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“…Since the readings do not appear to systematically drift in time, noise is likely the main source of variation, and assuming the variation is noise sets an upper limit to the noise level. A precision of 80 μm is similar to the 100 μm interobserver variation we found in measuring displacement of radiopaque tungsten wires in a pH sensor based on pH-responsive hydrogels swelling[41]. It is somewhat worse than RSA analysis of tantalum beads (20-50 μm), but an order of magnitude better than direct fracture gap motion analysis with plain film X-rays.…”

Section: Discussionsupporting

confidence: 57%

Measuring Orthopedic Plate Strain to Track Bone Healing Using a Fluidic Sensor Read via Plain Radiography

Rajamanthrilage

Arifuzzaman

Millhouse

et al. 2020

Preprint

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We describe a fluidic X-ray visualized strain indicator under applied load (X-VISUAL) to quantify orthopedic plate strain and inform rehabilitative care. This sensor uses a liquid-level gauge with hydro-mechanical amplification and is visualized in plain radiographs which are routinely acquired during patient recovery to find pathologies but are usually insufficient to quantify fracture stiffness. The sensor has two components: a stainless-steel lever which attaches to the plate, and an acrylic fluidic component which sits between the plate and lever. The fluidic component has a reservoir filled with radio-dense solution and an adjoining capillary wherein the fluid level is measured. When the plate bends under load, the lever squeezes the reservoir, which pushes the fluid along the channel. A tibial osteotomy model (5 mm gap) was used to simulate an unstable fracture, and allograft repair used to simulate a stiffer healed fracture. A cadaveric tibia and a mechanically equivalent composite tibia mimic were cyclically loaded five times (0 – 400 N axial force) while fluid displacement was measured from radiographs. The sensor displayed reversible and repeatable behavior with a slope of 0.096 mm/kg and fluid level noise of 50 to 80 micrometers (equivalent to 5-10 N). The allograft-repaired composite fracture was 13 times stiffer than the unstable fracture. An analysis of prior external fracture fixation studies and fatigue curves for internal plates indicates that the threshold for safe weight bearing should be 1/5th −1/10th of the initial bending for an unstable fracture. The precision of our device (<2% body weight) should thus be sufficient to track fracture healing from unstable through safe weight bearing.

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Section: Discussionsupporting

confidence: 57%

Measuring Orthopedic Plate Strain to Track Bone Healing Using a Fluidic Sensor Read via Plain Radiography

Rajamanthrilage

Arifuzzaman

Millhouse

et al. 2020

Preprint

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“…We also previously showed that the same hydrogel swelling was minimally affected by physiological variation in buffer and tryptic soy broth bacterial culture ionic strength, temperature (25–40 °C), or long term incubation in a highly oxidative environment with hydrogen peroxide and copper ions. [ 41 ]…”

Section: Resultsmentioning

confidence: 99%

“…First, it was performed only in ex vivo bovine synovial fluid with added HCl and NaOH to adjust the pH (and previously in buffers and bacterial cultures with varying temperature, sodium chloride concentration, and oxidative environment). [ 41 ] The in vivo response may be different, especially after long term implantation.…”

Section: Resultsmentioning

confidence: 99%

Synovial Fluid pH Sensor for Early Detection of Prosthetic Hip Infections

Wijayaratna

Kiridena

Adams

et al. 2021

Adv Funct Materials

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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.

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“…Upcoming smart implants will likely integrate different measurement parameters beyond the here outlined devices assessing the mechanical competence of a fracture. Other groups for example investigate the use of electrochemical sensors to measure oxygen saturation [33] or target detection of implant associated infection by implantable pH sensors [34] . Callus formation sequence from weekly X-rays correlates with the curve drop.…”

Section: The Future -Closing the Loop With Active Implantsmentioning

confidence: 99%

Smart implants in fracture care – only buzzword or real opportunity?

Ernst

Richards

Windolf

2021

Injury

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The assessment of fracture healing is still marked by a subjective and diffuse outcome due to the lack of clinically available quantitative measures. Without reliable information on the progression of healing and uniform criteria for union and non-union, therapeutic decision making, e.g. regarding the allowed weight bearing, hinges on the experience and the subjective evaluation of physicians. Already decades ago, fracture stiffness has been identified as a valid outcome measure for the maturity of the repair tissue. Despite early promising results, so far no method has made its way into practice beyond clinical studies. However, with current technological advancements and a general trend towards digital health care, measuring fracture healing seems to regain momentum. New generations of instrumented implants with sensoring capabilities, often termed as "smart implants", are under development. They target X-ray free and timely provision of reliable feedback upon the mechanical competence of the repair tissue and the healing environment to support therapeutic decision making and individualized after-care. With the gained experience from these devices, the next generations of smart implants may become increasingly sophisticated by internally analyzing the measured data and suggesting adequate therapeutic actions on their own.

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An implanted pH sensor read using radiography

Abstract: The constructed biosensor enhances the capability of traditional plain film radiography, enabling the noninvasive measurement of postoperative infection indicating chemical concentration such as pH on the implant surfaces.

Cited by 21 publications

References 44 publications

Measuring Orthopedic Plate Strain to Track Bone Healing Using a Fluidic Sensor Read via Plain Radiography

Measuring Orthopedic Plate Strain to Track Bone Healing Using a Fluidic Sensor Read via Plain Radiography

Synovial Fluid pH Sensor for Early Detection of Prosthetic Hip Infections

Smart implants in fracture care – only buzzword or real opportunity?

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