Miniaturized Capsule System Toward Real-Time Electrochemical Detection of H2 S in the Gastrointestinal Tract

Hydrogen sulfide (H2 S) is a gaseous inflammatory mediator and important signaling molecule for maintaining gastrointestinal (GI) homeostasis. Excess intraluminal H2 S in the GI tract has been implicated in inflammatory bowel disease and neurodegenerative disorders; however, the role of H2 S in disease pathogenesis and progression is unclear. Herein, an electrochemical gas-sensing ingestible capsule is developed to enable real-time, wireless amperometric measurement of H2 S in GI conditions. A gold (Au) three-electrode sensor is modified with a Nafion solid-polymer electrolyte (Nafion-Au) to enhance selectivity toward H2 S in humid environments. The Nafion-Au sensor-integrated capsule shows a linear current response in H2 S concentration ranging from 0.21 to 4.5 ppm (R2 = 0.954) with a normalized sensitivity of 12.4% ppm-1 when evaluated in a benchtop setting. The sensor proves highly selective toward H2 S in the presence of known interferent gases, such as hydrogen (H2 ), with a selectivity ratio of H2 S:H2 = 1340, as well as toward methane (CH4 ) and carbon dioxide (CO2 ). The packaged capsule demonstrates reliable wireless communication through abdominal tissue analogues, comparable to GI dielectric properties. Also, an assessment of sensor drift and threshold-based notification is investigated, showing potential for in vivo application. Thus, the developed H2 S capsule platform provides an analytical tool to uncover the complex biology-modulating effects of intraluminal H2 S.

Sensorized Endovascular Technologies: Additional Data to Enhance Decision-Making

BACKGROUND

Current endovascular procedures rely mostly on anatomic information, guided by fluoroscopy, to perform interventions (i.e. angioplasty, stent placement, coils). However, the structural parameters provided by these imaging technologies do not provide any physiological data on either the disease state or efficacy of intervention. Additional endovascular tools are needed to collect physiologic and other both anatomic and nonanatomic data to further individualize endovascular interventions with the ultimate goal of improving patient outcomes. This review details the current state of the art for these sensorized endovascular technologies and details systems under development with the aim of identifying gaps and new directions. The objective of this review was to survey the Vascular Surgery literature, engineering literature, and commercially available products to determine what exists in terms of sensor-enabled endovascular devices and where gaps and opportunities exist for further sensor integration.

METHODS

Search terms were entered into search engines such as Google and Google Scholar to identify endovascular devices containing sensors. A variety of terms were used including directly search for items such as "sensor-enabled endovascular devices" and then also completing more refined searches bases on areas of interest (i.e. fractional flow reserve, navigation, retrograde endovascular balloon occlusion of the aorta, etc.). For the most part, systems were included where the sensor was mounted directly onto the catheter and implantable sensors such as those that have been investigated for use with stents have been excluded.

RESULTS

The authors were able to identify a body of literature in the area of endovascular devices that contain sensors to measure physiologic information. However, areas where additional sensing capabilities may be useful were identified.

CONCLUSIONS

Several different types of sensors and sensing systems were identified that have been integrated with endovascular catheters. Although a great deal of work has been done in this field, there are additional useful data that could be obtained from additional novel sensing technologies. Furthermore, significant effort needs to be allocated to carefully studying how these new technologies can be employed to actually improve patient outcomes.

Recreating the Trabecular Outflow Tissue on Implantable, Micropatterned, Ultrathin, Porous Polycaprolactone Scaffolds

Glaucoma, where increased intraocular pressure (IOP) leads to damage to the optic nerve and loss of sight, is amongst the foremost causes of irreversible blindness worldwide. In primary open angle glaucoma, the increased IOP is a result of the malfunctioning human trabecular meshwork (HTM) cells' inability to properly regulate the outflow of aqueous humor from the eye. A potential future treatment for glaucoma is to replace damaged HTM cells with a tissue-engineered substitute, thus restoring proper fluid outflow. Polycaprolactone (PCL) is a versatile, biodegradable, and implantable material that is widely used for cell culture and tissue engineering. In this work, PCL scaffolds were lithographically fabricated using a sacrificial process to produce submicron-thick scaffolds with openings of specific sizes and shapes (e.g., grid, hexagonal pattern). The HTM cell growth on gelatin-coated PCL scaffolds was assessed by scanning electron microscopy, tetrazolium metabolic activity assay, and cytoskeletal organization of F-actin. Expression of HTM-specific markers and ECM deposition were assessed by immunocytochemistry and qPCR analysis. Gelatin-coated, micropatterned, ultrathin, porous PCL scaffolds with a grid pattern supported proper HTM cell growth, cytoskeleton organization, HTM-marker expression, and ECM deposition, demonstrating the feasibility of using these PCL scaffolds to tissue-engineer implantable, healthy ocular outflow tissue.

Freestanding region-responsive bilayer for functional packaging of ingestible devices

Ingestible capsules have the potential to become an attractive alternative to traditional means of treating and detecting gastrointestinal (GI) disease. As device complexity increases, so too does the demand for more effective capsule packaging technologies to elegantly target specific GI locations. While pH-responsive coatings have been traditionally used for the passive targeting of specific GI regions, their application is limited due to the geometric restrictions imposed by standard coating methods. Dip, pan, and spray coating methods only enable the protection of microscale unsupported openings against the harsh GI environment. However, some emerging technologies have millimeter-scale components for performing functions such as sensing and drug delivery. To this end, we present the freestanding region-responsive bilayer (FRRB), a packaging technology for ingestible capsules that can be readily applied for various functional ingestible capsule components. The bilayer is composed of rigid polyethylene glycol (PEG) under a flexible pH-responsive Eudragit® FL 30 D 55, which protects the contents of the capsule until it arrives in the targeted intestinal environment. The FRRB can be fabricated in a multitude of shapes that facilitate various functional packaging mechanisms, some of which are demonstrated here. In this paper, we characterize and validate the use of this technology in a simulated intestinal environment, confirming that the FRRB can be tuned for small intestinal release. We also show a case example where the FRRB is used to protect and expose a thermomechanical actuator for targeted drug delivery.

Integrated System for Bacterial Detection and Biofilm Treatment On Indwelling Urinary Catheters

GOAL

This work introduces an integrated system incorporated seamlessly with a commercial Foley urinary catheter for bacterial growth sensing and biofilm treatment.

METHODS

The system is comprised of flexible, interdigitated electrodes incorporated with a urinary catheter via a 3D-printed insert for impedance sensing and bioelectric effect-based treatment. Each of the functions were wirelessly controlled using a custom application that provides a user-friendly interface for communicating with a custom PCB via Bluetooth to facilitate implementation in practice.

RESULTS

The integrated catheter system maintains the primary functions of indwelling catheters - urine drainage, balloon inflation - while being capable of detecting the growth of Escherichia coli, with an average decrease in impedance of 13.0% after 24 hours, tested in a newly-developed simulated bladder environment. Furthermore, the system enables bioelectric effect-based biofilm reduction, which is performed by applying a low-intensity electric field that increases the susceptibility of biofilm bacteria to antimicrobials, ultimately reducing the required antibiotic dosage.

CONCLUSION

Overall, this modified catheter system represents a significant step forward for catheter-associated urinary tract infection (CAUTI) management using device-based approaches, integrating flexible electrodes with an actual Foley catheter along with the control electronics and mobile application.

SIGNIFICANCE

CAUTIs, exacerbated by the emergence of antibiotic-resistant pathogens, represent a significant challenge as one of the most prevalent healthcare-acquired infections. These infections are driven by the colonization of indwelling catheters by bacterial biofilms.

Submarine medicine: An overview of the unique challenges, medical concerns, and gaps

Submariners face many challenges. For example, they "live where they work" and can be called to duty anytime. They have limited access to open space, natural settings, fresh air, fresh food, sunlight, privacy, exercise, and outside communication. They support a wider range of missions than occur aboard most other Navy vessels. At sea or on shore, submariners work long hours under conditions with little margin for error. They may traverse remote or disputed areas of the ocean far from rescue assets, and must remain vigilant for potential encounters with hostile forces, onboard fires, anomalies in the breathing atmosphere, leaks, undersea collisions, or radiation exposures. If any of these factors cause casualties, the Independent Duty Corpsman (with intermittent advice from shore-based medical personnel), must be ready to provide aid as long as necessary. The challenges of submarine service led to the growth of the unique field of submarine medicine, which has maintained an excellent record of health and safety. This review introduces the field of submarine medicine as practiced in the U.S. Navy, describing its major concerns, giving an overview of the operation of a submarine medical department, and identifying several medical gaps that researchers are working to fill. Submarine medicine already has a stellar record in terms of radiation and atmospheric safety and has made strides in fatigue management. Ongoing work will deliver improved psychological screening and support tools. This report summarizes developments in these and other areas of submarine medicine.

Capacitive sensing of triglyceride film reactions: a proof-of-concept demonstration for sensing in simulated duodenal contents with gastrointestinal targeting capsule system

Ingestible capsule systems continue to evolve to overcome drawbacks associated with traditional gastrointestinal (GI) diagnostic and therapeutic processes, such as limitations on which sections of the GI tract can be accessed or the inability to measure local biomarker concentrations. We report an integrated capsule sensing system, utilizing a hybrid packaging scheme coupled with triglyceride film-coated capacitive sensors, for measuring biochemical species present in the duodenum, such as pancreatic lipase and bile acids. The system uses microfabricated capacitive sensors interfaced with a Bluetooth low-energy (BLE)-microcontroller, allowing wireless connectivity to a mobile app. The triglyceride films insulate the sensor surface and react either with 0.01-1 mM lipase via hydrolysis or 0.07-7% w/v bile acids via emulsification in simulated fluids, leading to measurable changes in capacitance. Cross reactivity of the triglyceride films is evaluated in both phosphate buffered saline (PBS) as well as pancreatic trypsin solutions. The film morphology is observed after exposure to each stimulus to better understand how these changes alter the sensor capacitance. The capsule utilizes a 3D-printed package coated with polymers that remain intact in acid solution (mimicking gastric conditions), then dissolve at a duodenum-mimicking neutral pH for triggered opening of the sensing chamber from which we can subsequently detect the presence of pancreatic lipase. This device strategy represents a significant step towards using embedded packaging and triglyceride-based materials to target specific regions of the GI tract and sensing biochemical contents for evaluating gastrointestinal health.

Ingestible Sensors and Sensing Systems for Minimally Invasive Diagnosis and Monitoring: The Next Frontier in Minimally Invasive Screening

Ingestible electronic systems that are capable of embedded sensing, particularly within the gastrointestinal (GI) tract and its accessory organs, have the potential to screen for diseases that are difficult if not impossible to detect at an early stage using other means. Furthermore, these devices have the potential to (1) reduce labor and facility costs for a variety of procedures, (2) promote research for discovering new biomarker targets for associated pathologies, (3) promote the development of autonomous or semiautonomous diagnostic aids for consumers, and (4) provide a foundation for epithelially targeted therapeutic interventions. These technological advances have the potential to make disease surveillance and treatment far more effective for a variety of conditions, allowing patients to lead longer and more productive lives. This review will examine the conventional techniques, as well as ingestible sensors and sensing systems that are currently under development for use in disease screening and diagnosis for GI disorders. Design considerations, fabrication, and applications will be discussed.

In-Plane Vibration of Hammerhead Resonators for Chemical Sensing Applications

Thermally excited and piezoresistively detected in-plane cantilever resonators have been previously demonstrated for gas- and liquid-phase chemical and biosensing applications. In this work, the hammerhead resonator geometry, consisting of a cantilever beam supporting a wider semicircular "head", vibrating in an in-plane vibration mode, is shown to be particularly effective for gas-phase sensing with estimated limits of detection in the sub-ppm range for volatile organic compounds. This paper discusses the hammerhead resonator design and the particular advantages of the hammerhead geometry, while also presenting mechanical characterization, optical characterization, and chemical sensing results. These data highlight the distinct advantages of the hammerhead geometry over other cantilever designs.

Flexible Platform for In Situ Impedimetric Detection and Bioelectric Effect Treatment of Escherichia Coli Biofilms

GOAL

This paper reports a platform for real-time monitoring and treatment of biofilm formation on three-dimensional biomedical device surfaces.

METHODS

We utilize a flexible platform consisting of gold interdigitated electrodes patterned on a polyimide substrate. The device was integrated onto the interior of a urinary catheter and characterization was performed in a custom-developed flow system. Biofilm growth was monitored via impedance change at 100 Hz ac with a 50 mV signal amplitude.

RESULTS

A 30% impedance decrease over 24 h corresponded to Escherichia coli biofilm formation. The platform also enabled removal of the biofilm through the bioelectric effect; a low concentration of antibiotic combined with the applied ac voltage signal led to a synergistic reduction in biofilm resulting in a 12% increase in impedance. Biomass characterization via crystal violet staining confirmed that the impedance detection results correlate with changes in the amount of biofilm biomass on the sensor. We also demonstrated integration with a chip-based impedance converter to enable miniaturization and allow in situ wireless implementation. A 5% impedance decrease measured with the impedance converter corresponded to biofilm growth, replicating the trend measured with the potentiostat.

CONCLUSION

This platform represents a promising solution for biofilm infection management in diverse vulnerable environments.

SIGNIFICANCE

Biofilms are the dominant mode of growth for microorganisms, where bacterial cells colonize hydrated surfaces and lead to recurring infections. Due to the inaccessible nature of the environments where biofilms grow and their increased tolerance of antimicrobials, identification, and removal on medical devices poses a challenge.

A simple sensing mechanism for wireless, passive pressure sensors

We have developed a simple wireless pressure sensor that consists of only three electrically isolated components. Two conductive spirals are separated by a closed cell foam that deforms when exposed to changing pressures. This deformation changes the capacitance and thus the resonant frequency of the sensors. Prototype sensors were submerged and wirelessly interrogated while being exposed to physiologically relevant pressures from 10 to 130 mmHg. Sensors consistently exhibited a sensitivity of 4.35 kHz/mmHg which is sufficient for resolving physiologically relevant pressure changes in vivo. These simple sensors have the potential for in vivo pressure sensing.

Reducing the effect of parasitic capacitance on implantable passive resonant sensors

Passive, LC resonators have the potential to serve as small, robust, low cost, implantable sensors to wirelessly monitor implants following orthopedic surgery. One significant barrier to using LC sensors is the influence on the sensor's resonance of the surrounding conductive high permittivity media in vivo. The surrounding media can detune the resonant frequency of the LC sensor resulting in a bias. To mitigate the effects of the surrounding media, we added a "capping layer" to LC sensors to isolate them from the surrounding media. Several capping materials and thicknesses were tested to determine effectiveness at reducing the sensor's interaction with the surrounding media. Results show that a 1 mm glass capping layer on the outer surfaces of the sensor was sufficient to reduce the effects of the media on sensor signal to less than 1%.

A sacrificial process for fabrication of biodegradable polymer membranes with submicron thickness

A new sacrificial molding process using a single mask has been developed to fabricate ultrathin 2-dimensional membranes from several biocompatible polymeric materials. The fabrication process is similar to a sacrificial microelectromechanical systems (MEMS) process flow, where a mold is created from a material that can be coated with a biodegradable polymer and subsequently etched away, leaving behind a very thin polymer membrane. In this work, two different sacrificial mold materials, silicon dioxide (SiO2 ) and Liftoff Resist (LOR) were used. Three different biodegradable materials; polycaprolactone (PCL), poly(lactic-co-glycolic acid) (PLGA), and polyglycidyl methacrylate (PGMA), were chosen as model polymers. We demonstrate that this process is capable of fabricating 200-500 nm thin, through-hole polymer membranes with various geometries, pore-sizes and spatial features approaching 2.5 µm using a mold fabricated via a single contact photolithography exposure. In addition, the membranes can be mounted to support rings made from either SU8 or PCL for easy handling after release. Cell culture compatibility of the fabricated membranes was evaluated with human dermal microvascular endothelial cells (HDMECs) seeded onto the ultrathin porous membranes, where the cells grew and formed confluent layers with well-established cell-cell contacts. Furthermore, human trabecular meshwork cells (HTMCs) cultured on these scaffolds showed similar proliferation as on flat PCL substrates, further validating its compatibility. All together, these results demonstrated the feasibility of our sacrificial fabrication process to produce biocompatible, ultra-thin membranes with defined microstructures (i.e., pores) with the potential to be used as substrates for tissue engineering applications. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 104B: 1192-1201, 2016.

Mass-sensitive detection of gas-phase volatile organics using disk microresonators

The detection of volatile organic compounds (VOCs) in the gas phase by mass-sensitive disk microresonators is reported. The disk resonators were fabricated using a CMOS-compatible silicon micromachining process and subsequently placed in an amplifying feedback loop to sustain oscillation. Sensing of benzene, toluene, and xylene was conducted after applying controlled coatings of an analyte-absorbing polymer. An analytical model of the resonator's chemical sensing performance was developed and verified by the experimental data. Limits of detection for the analytes tested were obtained, modeled, and compared to values obtained from other mass-sensitive resonant gas sensors.

Liquid-phase chemical sensing using lateral mode resonant cantilevers

Liquid-phase operation of resonant cantilevers vibrating in an out-of-plane flexural mode has to date been limited by the considerable fluid damping and the resulting low quality factors (Q factors). To reduce fluid damping in liquids and to improve the detection limit for liquid-phase sensing applications, resonant cantilever transducers vibrating in their in-plane rather than their out-of-plane flexural resonant mode have been fabricated and shown to have Q factors up to 67 in water (up to 4300 in air). In the present work, resonant cantilevers, thermally excited in an in-plane flexural mode, are investigated and applied as sensors for volatile organic compounds in water. The cantilevers are fabricated using a complementary metal oxide semiconductor (CMOS) compatible fabrication process based on bulk micromachining. The devices were coated with chemically sensitive polymers allowing for analyte sorption into the polymer. Poly(isobutylene) (PIB) and poly(ethylene-co-propylene) (EPCO) were investigated as sensitive layers with seven different analytes screened with PIB and 12 analytes tested with EPCO. Analyte concentrations in the range of 1-100 ppm have been measured in the present experiments, and detection limits in the parts per billion concentration range have been estimated for the polymer-coated cantilevers exposed to volatile organics in water. These results demonstrate significantly improved sensing properties in liquids and indicate the potential of cantilever-type mass-sensitive chemical sensors operating in their in-plane rather than out-of-plane flexural modes.