A subscription to JoVE is required to view this content. Sign in or start your free trial.
The manuscript presents a miniature implantable pH sensor with ASK modulated wireless output together with a fully passive receiver circuit based on zero-bias Schottky diodes. This solution can be used as a basis in the development of in vivo calibrated electrostimulation therapy devices and for ambulatory pH monitoring.
Ambulatory pH monitoring of pathological reflux is an opportunity to observe the relationship between symptoms and exposure of the esophagus to acidic or non-acidic refluxate. This paper describes a method for the development, manufacturing, and implantation of a miniature wireless-enabled pH sensor. The sensor is designed to be implanted endoscopically with a single hemostatic clip. A fully passive rectenna-based receiver based on a zero-bias Schottky diode is also constructed and tested. To construct the device, a two-layer printed circuit board and off-the-shelf components were used. A miniature microcontroller with integrated analog peripherals is used as an analog front end for the ion-sensitive field-effect transistor (ISFET) sensor and to generate a digital signal which is transmitted with an amplitude shift keying transmitter chip. The device is powered by two primary alkaline cells. The implantable device has a total volume of 0.6 cm3 and a weight of 1.2 grams, and its performance was verified in an ex vivo model (porcine esophagus and stomach). Next, a small footprint passive rectenna-based receiver which can be easily integrated either into an external receiver or the implantable neurostimulator, was constructed and proven to receive the RF signal from the implant when in proximity (20 cm) to it. The small size of the sensor provides continuous pH monitoring with minimal obstruction of the esophagus. The sensor could be used in routine clinical practice for 24/96 h esophageal pH monitoring without the need to insert a nasal catheter. The "zero-power" nature of the receiver also enables the use of the sensor for automatic in-vivo calibration of miniature lower esophageal sphincter neurostimulation devices. An active sensor-based control enables the development of advanced algorithms to minimize the used energy to achieve a desirable clinical outcome. One of the examples of such an algorithm would be a closed-loop system for on-demand neurostimulation therapy of gastroesophageal reflux disease (GERD).
The Montreal Consensus defines gastroesophageal reflux disease (GERD) as "a condition that develops when refluxing the contents of the stomach causes unpleasant symptoms and/or complications". It may be associated with other specific complications such as esophageal strictures, Barrett's esophagus, or esophageal adenocarcinoma. GERD affects approximately 20% of the adult population, mainly in countries with high economic status1.
Ambulatory pH monitoring of pathological reflux (acid exposure time of more than 6%) allows us to distinguish the relationship between symptoms and acidic or non-acidic gastroeso....
No living animals were involved in this study. The experiment was performed on an ex vivo model consisting of a porcine esophagus and stomach. The stomach and esophagus were purchased from a local butchery as their standard product. This procedure is in accordance with Czech laws, and we prefer it because of the "3R" principle (Replacement, Reduction, and Refinement).
1. Fabrication of the pH sensor assembly
NOTE: Observe precautions for handling elec.......
A device capable of autonomous pH sensing and wireless transmitting of the pH value was successfully constructed, as shown in Figure 8. The constructed device is a miniature model; it weighs 1.2 g and has a volume of 0.6 cm3. The approximate dimensions are 18 mm x 8.5 mm x 4.5 mm. As shown in Figure 15, Figure 16, and Figure 17, it can be implanted to the proxi.......
This method is suitable for researchers who work on the development of novel active implantable medical devices. It requires a level of proficiency in the manufacturing of electronic prototypes with surface mount components. The critical steps in the protocol are related to the manufacturing of the electronics, especially populating the PCBs, which is prone to operator error in placement and soldering of small components. Then, correct encapsulation is crucial to prolong the lifetime of the device when exposed to moistur.......
The authors gratefully acknowledge Charles University (project GA UK No 176119) for supporting this study. This work was supported by the Charles University research program PROGRES Q 28 (Oncology).
....Name | Company | Catalog Number | Comments |
AG1 battery | Panasonic | SR621SW | Two batteries per one implant |
Battery holder | MYOUNG | MY-521-01 | |
Copper enamel wire for the antenna | pro-POWER | QSE Wire - 0.15 mm diameter, 38 SWG | |
Epoxy for encapsulation | Loctite | EA M-31 CL | Two-part medical-grade ISO10993 compliant epoxy |
FEP cable for pH sensor | Molex / Temp-Flex | 100057-0273 | |
Flux cleaner | Shesto | UTFLLU05 | Prepare 5% solution in deionized water for cleaning by sonication |
Hemostatic clip | Boston Scientific | Resolution | |
Hot air gun + soldering iron | W.E.P. | Model 706 | Any soldering iron capable of soldering with tin and hot-air gun capable of maintaining 260 °C can be used |
Impedance matching software | Iowa Hills Software | Smith Chart | Can be downloaded from http://www.iowahills.com/9SmithChartPage.html - alternatively, any RF design software supports calculation of impedance matching components |
ISFET pH sensor on a PCB | WinSense | WIPS | Order a model pre-mounted on a PCB with on-chip gold reference electrode |
Laboratory pH meter | Hanna Instruments | HI2210-02 | Used with HI1131B glass probe |
Microcontorller programmer | Microchip | PICkit 3 | Other PIC16 compatible programmers can be also used |
Pig stomach with esophagus | Local pig farm | Obtained from approx. 40–50 kg pig | It is important that the stomach includes a full length of the esophagus. |
Printed circuit board - receiver | Choose preferred PCB supplier | According to pcb2.zip data | One layer, 0.8 mm thickness, FR4, no mask |
Printed circuit board - sensor | Choose preferred PCB supplier | According to pcb1.zip data | Two-layer with PTH, 0.6 mm thickness, FR4, 2x mask |
Receiver - 0R | Vishay | CRCW04020000Z0EDC | See Figure 12 and Figure 13 for placement |
Receiver - 1.5 pF | Murata | GRM0225C1C1R5CA03L | See Figure 12 and Figure 13 for placement |
Receiver - 100 pF | Murata | GRM0225C1E101JA02L | See Figure 12 and Figure 13 for placement |
Receiver - 33 nH | Pulse Electronics | PE-0402CL330JTT | See Figure 12 and Figure13 for placement |
Receiver - RF schottky diodes | MACOM | MA4E2200B1-287T | See Figure 12 and Figure 13 for placement |
Receiver - SMA antenna | LPRS | ANT-433MS | |
Receiver - SMA connector | Linx Technologies | CONSMA001 | See Figure 12 and Figure 13 for placement |
Sensor - C1 | Murata | GRM0225C1H8R0DA03L | 8 pF 0402 capacitor |
Sensor - C2 | Murata | GRM0225C1H8R0DA03L | 8 pF 0402 capacitor |
Sensor - C3 | Murata | GCM155R71H102KA37D | 1 nF 0402 capacitor |
Sensor - C4 | Murata | GRM0225C1H1R8BA03L | 1.8 pF |
Sensor - C5 | Vishay | CRCW04020000Z0EDC | Place 0R 0402 resistor or use to match the antenna |
Sensor - C6 | Murata | GRM155C81C105KE11J | 1 uF 0402 capacitor |
Sensor - C7 | Murata | GRM155C81C105KE11J | 1 uF 0402 capacitor |
Sensor - C8 | Murata | GRM022R61A104ME01L | 100 nF 0402 capacitor |
Sensor - IC1 | Microchip | MICRF113YM6-TR | MICRF113 RF transmitter |
Sensor - IC2 | Microchip | PIC16LF1704-I/ML | PIC16LF1704 low-power microcontroller |
Sensor - R1 | Vishay | CRCW040210K0FKEDC | 10 kOhm 0402 resistor |
Sensor - R2 | Vishay | CRCW040233K0FKEDC | 33 kOhm 0402 resistor |
Sensor - R3 | Vishay | CRCW04021K00FKEDC | 1 kOhm 0402 resistor |
Sensor - R5 | Vishay | CRCW040210K0FKEDC | 10 kOhm 0402 resistor |
Sensor - X1 | ABRACON | ABM8W-13.4916MHZ-8-J2Z-T3 | 3.2 x 2.5 mm 13.4916 MHz 8 pF crystal |
Titanium wire | Sigma-Aldrich | GF36846434 | 0.125 mm titanium wire |
Vector network analyzer | mini RADIO SOLUTIONS | miniVNA Tiny | Other vector network analyzers can be used - the required operation frequency is 300–500 MHz, resolution bandwidth equal or lower than 1 MHz, output power of no more than 0 dBm and dynamic range preferably better than 60 dB for the receiving front-end |
This article has been published
Video Coming Soon
ABOUT JoVE
Copyright © 2024 MyJoVE Corporation. All rights reserved