Autonomous and Rechargeable Microneurostimulator Endoscopically Implantable into the Submucosa

Summary

The application of high-frequency low-energetic stimulation can alleviate the symptoms of gastric dysmotility. In this research, a miniature, endoscopically implantable and wirelessly rechargeable device which is implanted into a submucosal pocket is presented. Successful both-way communication and stimulation control were achieved during an experiment on live pig.

Abstract

Gastric dysmotility can be a sign of common diseases such as longstanding diabetes mellitus. It is known that the application of high-frequency low-energetic stimulation can help to effectively moderate and alleviate the symptoms of gastric dysmotility. The goal of the research was the development of a miniature, endoscopically implantable device to a submucosal pocket. The implantable device is a fully customized electronic package which was specifically designed for the purpose of experiments in the submucosa. The device is equipped with a lithium-ion battery which can be recharged wirelessly by receiving an incident magnetic field from the charging/transmitting coil. The uplink communication is achieved in a MedRadio band at 432 MHz. The device was endoscopically inserted into the submucosal pocket of a live domestic pig used as an in vivo model, specifically in the stomach antrum. The experiment confirmed that the designed device can be implanted into the submucosa and is capable of bidirectional communication. The device can perform bipolar stimulation of muscle tissue.

Introduction

Gastric dysmotility can be a sign of several relatively common diseases such as gastroparesis, which is usually characterized by a chronic progression and imposes rather severe consequences on the social, work-related, and physical status of the patient. Most cases of gastroparesis are usually diabetic or idiopathic in origin and are often resistant to available medication¹. Patients afflicted with this condition most commonly present with nausea and repeated vomiting. Based on previous research, it is known that the application of high-frequency low-energetic electrical stimulation can help to effectively moderate and alleviate the symptoms of gastric dysmotility^1,2.

Based on previous studies, it is proven that high-frequency gastric electrical stimulation can significantly improve the symptoms and gastric emptying³. It has also been shown that lower esophageal sphincter neurostimulator therapy is safe and effective for the treatment of gastroesophageal reflux disease (GERD), reducing the acid exposure and eliminating daily proton-pump inhibitor (PPI) usage without stimulation related adverse effects⁴. Before human trials, first studies were performed in animal models (canine models⁵). Based on these studies, electrical stimulation of the lower esophageal sphincter (LES, 20 Hz, pulse width of 3 ms) caused a prolonged contraction of the LES⁵. Similar effects of high (20 Hz, pulse width of 200 μs) and low (6 cycles/min, pulse width of 375 ms) frequency electrical stimulation on LES in GERD patients were investigated. Both high and low frequency stimulation were effective⁶. However, currently, there are only two neurostimulation devices for gastric or esophageal stimulation available on the market^7,8. In those devices, the electrodes can be implanted surgically, laparoscopically or robotically. The device itself is implanted subcutaneously. This requires general anaesthesia and have a bulky device fitted, using intramuscular catheters which allow for the stimulation of the gastric or esophageal muscle tissue. So, the option of using a wirelessly communicating device implanted into the gastric submucosal layer would represent a definite advantage and improvement in patient comfort. As stated in the previous research^9,10, it was proven that an implantation of a miniature neurostimulator into submucosa is possible. For the endoscopic submucosal implantation, we use a technique called endoscopic submucosal pocketing (ESP), based on endoscopic submucosal tunnel dissection¹⁰. The goal of this research is to further improve this concept of an implantable neurostimulator, primarily in the scope of power management (specifically the wireless recharging capability), conformity with respective laws and regulations for wireless communication links in medical implantable devices and possibility of bipolar neurostimulation. Next, the presented microneurostimulator is capable of bidirectional communication and the stimulation parameters can be changed in real-time, even while the device is implanted.

This technique is suitable for teams with a therapeutic endoscopist experienced in endoscopic pocketing or tunnel dissections. Next, a hardware and embedded software designer with experience in building hardware prototypes with microcontrollers and radio frequency circuits using surface mount technology is needed. For building the hardware prototypes, a lab equipped with a reflow soldering station and basic equipment for electrical measurements (at least a digital multimeter, an oscilloscope, a spectrum analyzer and PICkit3 programmer) is required.

Protocol

All endoscopic procedures including animal subjects have been approved at the Institute of Animal Physiology and Genetics, Academy of Science Czech Republic (Biomedical Center PIGMOD), Libechov, Czech Republic (project Experiments in implantation of battery-less and battery devices into submucosa of the esophagus and stomach — experimental study). All experiments are done in compliance with Czech law 246/1992 Sb. "On the protection of animals against maltreatment, as amended". Transmitter device is not required to be sterilized, because it is an external device that is not in direct contact with the animal.

1. Implantable Device Design

1. Prepare the PCB using a third-party PCB manufacturing service. The complete printed circuit board design is provided in the supplementary file "gerber_implant.7z". The schematic diagram is provided in Figure 1.
2. Place the PCBs on a flat surface (Figure 2a). Use a solder paste dispenser with 0.6 mm needle and 60 psi pressure to manually dispense the soldering paste onto every metallic pad on the PCB. Begin with the top side of the PCB (Figure 2b). The total amount of soldering paste for both sides of the PCB should not exceed 15 μL.
3. With a pair of antistatic tweezers, place all components on the top layer of the PCB (Figure 2e). Use Figure 3 for component position and supplementary file "bom_implantabledevice.csv" for the assignment of components to their numbers.
4. Use a PCB hot air gun station at 260 °C to solder all components (Figure 4a). Wait until all the solder paste melts, then put away the hot air gun and allow the board cool to room temperature.
5. Turn the PCB over and dispense solder paste on the other side. Use the same needle and pressure as stated in 1.2 (Figure 2d).
6. As in step 1.3., place all components of the bottom layer of the PCB. Refer to Figure 3 for component position and the supplementary file "bom_implantabledevice.csv" for the assignment of components to their numbers.
7. Repeat the heating of the PCB with a hot air gun to solder all components on the bottom side. Use the same process as in step 1.4.
8. Check the PCB for any short circuits visually. If any short circuit is found, remove it with a soldering iron.
9. Manufacture the wireless charging/communication coil. Use 17 turns of AWG42 wire. The size of the coil is 26 x 13.5 mm² (Figure 4d). Twist the two output wires.
10. Design and manufacture the electrode. The electrode design is provided in the supplementary file "gerber_electrodes.7z". Use the same manufacturing process as in step 1.1. This PCB is fully completed after manufacturing, and no components are required to be soldered onto it. Solder two AWG42 wires to the small rectangular contacts (Figure 4f)
11. Prepare the antenna by using 7 cm of enameled wire and scraping off 3 mm of the enamel from one end (Figure 4e)
12. Connect the PICkit 3 programmer to the PCB (Figure 4b-c)
    1. Connect pads 6 and 7, according to Figure 5, to pins 2 and 3 of the PICkit programmer, respectively.
    2. Connect pads TP1, TP2 and TP3 (refer to Figure 3) to pins 1, 5 and 4 of the PICkit programmer, respectively
13. Plug in the PICkit 3 programmer into the USB port of a computer with MPLAB IPE software installed.
14. Run the MPLAB IPE software and program the firmware into the microcontroller.
    1. Run the MPLAB IPE v3.61. Select "Settings | Advanced Mode"
    2. Into the Password field, enter the default password which is 'microchip'. Click "Log on". A tab with different panels on the left will appear.
    3. On the top left, click "Operate", then in top middle part of the screen, click "Device field" and type in "PIC16LF1783". Click "Apply".
    4. Select panel "Power" on the left (Figure 6).
    5. Change the VDD voltage value to 2.55. This step is critical.
       Caution: Setting this value above 2.8 V will damage the board (Figure 7).
    6. Click the checkbox "Power Target Circuit" from "Tool" (Figure 7).
    7. Click the "Operate" tab on the left (Figure 6).
    8. Click "Connect".
    9. Download the supplementary file "IMPLANTABLE_V2.X.production.hex" and note its location on the hard drive. In the IPE software, find the Source line and click the "Browse" button near it (Figure 8).
    10. Click Program. Wait till the software says that the software has been successfully downloaded to the microcontroller (Figure 9).
15. Desolder the wires soldered to pads TP1, TP2 and TP3 (Figure 3) as well as wires soldered to pads 6 and 7 (Figure 5).
16. Connect the PCB to all other electrical components except for the battery (Figure 10a).
    1. Solder the wireless charging/communication coil to pads 2 and 3 according to Figure 8. The polarity is not important.
    2. Connect the antenna to pad 1 according to Figure 5. Connect the PCB electrodes to pads number 4 and 5 according to Figure 5. The polarity is not important.
17. Solder the CG-320 battery to pads 6 and 7 (Figure 5). The negative terminal of the battery must be soldered onto pad 7. Be careful while performing the next steps. The device is now powered and is sensitive to short circuits and contact with metallic objects.
18. To test the functionality of the wireless charging circuitry, all steps in part 2 need to be completed. After that, place the wireless charger/transmitter in close proximity of the device. Use a multimeter to measure the voltage of the battery. If the battery voltage is slowly rising (several mV per min), the charging function is working.
19. Wind the antenna around the device in a spiral (Figure 10b)
20. Cut a 32 mm long piece of a heat-shrinkable tubing with an internal diameter of 9.5 mm.
21. Place the coil on the PCB. Refer to Figure 7b for the correct placement.
22. Put the heat-shrinkable tubing over the device, coil and antenna. Only the electrodes should protrude from the tubing. Refer to Figure 7c for correct placement.
23. Heat the tubing with a hot air gun to 150 °C to shrink and then allow it to cool (Figure 10d).
24. Apply epoxy glue to the left end to seal one side of the tubing (Figure 10e).
25. Glue the electrode to the back side of the PCB with tubing. Also glue the other end of the tubing. Refer to Figure 10f for correct placement.
26. Wait for at least 24 h for the glue to harden and fully cure.
27. After the completion of the wireless charger/transmitter device, test the implantable device for water leaks by placing it into a 30 cm high column of saturated saline solution for 1 h. Any major leak can be spotted as a sudden drop of the battery voltage or the malfunction of the device caused by the saline solution shorting the electronics. After the test, the device is fully prepared to be implanted.
28. Test the stimulation function of the implant using an oscilloscope. Connect two measurement electrodes of the oscilloscope to the tin metal plated contact pads of the electrode on the implantable device. Observe the stimulation pattern on the oscilloscope screen. The correct stimulation pattern is given in Figure 11.

2. Wireless Charger/Transmitter Design

1. The PCB design is provided in the supplementary file "gerber_transmitter.7z". Use the same manufacturing process as for the implantable device. The schematic diagram is provided in Figure 12.
2. Place the PCBs on a flat surface. Use a solder paste dispenser with 0.6 mm needle and 60 psi pressure to manually dispense the soldering paste onto every metallic pad on the PCB. The total amount of solder paste dispensed on the PCB should not exceed 50 μL.
3. With a pair of antistatic tweezers, place all components on the top layer of the PCB. Consult Figure 13 for the component position and the supplementary file "bom_transmitterdevice.csv" for the assignment of components to their numbers.
4. Use a PCB hot air gun station preset to 260 °C to solder all components. Wait until all the solder paste melts, put away the hot air gun and allow the board to cool to room temperature.
5. Repeat the steps 2.3–2.4 for the bottom side of the device. Follow a similar procedure as during the manufacturing of the implantable device.
6. Create a coil with 3 turns of AWG18 enameled wire (Figure 14c) and connect it to pads COIL1 and COIL2 (Figure 13).
7. Make an aluminum heatsink for the power transistors (Figure 13, Q1 and Q2). The exact shape of the heatsink is not critical. One of the possible embodiments is shown in Figure 9d. In this case, the heatsink also forms an enclosure for the device.
8. Connect the PICkit 3 programmer to the assembled PCB. Connect pads TP1 to TP5 (Figure 13) with pins 1 to 5 of the PICkit programmer, respectively.
9. Plug in the PICkit 3 programmer into the USB port of a computer with MPLAB IPE software installed.
10. Run the MPLAB IPE software and program the firmware into the microcontroller. The process is the same as for the implantable device, except for the VDD voltage and file uploaded.
    1. Run the MPLAB IPE v3.61. Select "Settings | Advanced Mode".
    2. Into password box, enter the default password which is 'microchip'. Click "Log on". A tab with different panels on the left will appear.
    3. On the top left, click "Operate", then in the top middle part of the screen, click the "Device" and type in "PIC16LF1783". Click "Apply".
    4. Select panel "Power" on the left
    5. Change the VDD voltage value to 3.3.
    6. Click the checkbox "Power Target Circuit" from "Tool".
    7. Click the "Operate" tab on the left.
    8. Click "Connect".
    9. Download the supplementary file "IMPLANTABLE_V2_TRANSMITTER.X.production.hex" and note its location on the hard drive. In the IPE software, find the Source line and click the "Browse" button near to it.
    10. Click "Program". Wait till the software says that the software was downloaded to the microcontroller successfully.
11. Desolder the wires soldered to pads TP1 to TP5
12. Connect a 12 V power supply to the V- and V+ pads (Figure 5). The negative terminal has to be connected to the V- pad.
13. Plug in a mini-USB to USB-A cable to the X1 connector (Figure 5) and connect to a computer with PuTTy software pre-installed.
14. Open the PuTTY software and set it up (Figure 15).
    1. Open the PuTTY software. Select "Serial" as connection type.
    2. Enter COMx as a Serial line, where x is the number of the COM port of the device. If no other COM port device was installed, this number will be 1.
    3. Enter "38400" as Speed. Click "Open". The charger/transmitter device is now ready to be used. Press H key for help.

3. Endoscopic Implantation

1. Use a live mini pig as an in vivo model, adult (8-36 months), 20-30 kg weight.
   1. Let the pig fast for 24 h prior to the procedure.
   2. Allow clear liquids ad libitum.
   3. Administer intramuscular tiletamine (2 mg/kg), zolazepam (2 mg/kg) and ketamine (11 mg/kg) as a premedication.
   4. Apply intravenous thiopental ad effectum (5% solution) and inhalation anesthesia with isoflurane, N₂O and propofol injection. Proper anesthesia is confirmed by reflexes and muscle tone, eye position, palpebral reflex and pupillary reflex. Circulation, oxygenation, ventilation and body temperature are continuously monitored.
2. In order to perform the implantation and visualization, use an animal model dedicated endoscope. Insert it using the standard way into the in vivo model.
3. Grasp the device externally with a snare. After that, insert it into the stomach, then release it.
4. Extract the endoscope, equip it with a dissection cap (15.5 mm), and then re-insert it to the stomach.
5. In order to implant the device to submucosa, apply saline solution mixed with methylene blue into the submucosal layer using an injection therapy needle catheter (25 G).
6. Make a horizontal incision to create an opening in the submucosa using an electrosurgical knife with a knob-shaped tip.
7. Using the affixed cap, insert the cap into the newly created space, and with the use of an electrosurgical knife, continue disrupting, dilating, and dissecting the submucosal layer, creating a sufficiently large-enough pocket to insert the stimulation device.
8. Grasp the device which is lying freely inside the stomach with insertion and extraction loops and, using grasping forceps, navigate it into the submucosal pocket. Place the stimulation electrodes in contact with the muscularis propria using grasp forceps.
9. Use an over the scope clip to secure the device in place inside the submucosal pocket and prevent any migration or dislodging.

4. Experiment — After Implantation

1. After successful implantation, place the charger/transmitter coil in proximity of the implanted device.
2. Plug in the RTL2832 dongle in the PC.
3. Run the HDSDR software and set the center frequency to 432 MHz.
   1. Open the HDSDR software (Figure 15) for correct settings and PuTTY software (Figure 16). In the HDSDR software, click "Options | Select Input | ExtIO".
   2. Select Bandwidth — "960000". Select the LO frequency to 431.95 MHz. Select the Tune frequency to 432.00 MHz.
4. Transmit a Manchester coded sequence from the charger/transmitter by pressing the R key in the PuTTY terminal and receive the OOK modulated reply from the implant by observation of the main HDSDR window ( Figure 17e-f).

5. Euthanasia after the Experiment

1. Use an anesthetic overdose for euthanasia (lethal dose of thiopental and KCl).

Results

Figure 17 shows that an endoscopic placement of the gastric neurostimulator into a pocket in submucosa as well as proper placement of the electrodes to the muscular layer was successful. The dimensions of the device (Figure 10) are 35 x 15 x 5 mm³ while the weight is 2.15 g. Figure 17 shows the circuit diagram of the device showing that the device comprises of 6 different modules whic...

Discussion

The design of the implantable device should primarily focus on the overall size of the device, achievable stimulation profiles (maximum voltage, maximum deliverable current, length of pulses and pulse frequency). Main limitation from the hardware perspective is the size and availability of suitable components. To minimize the overall size, surface mount components are preferred because of their compact packaging. The best solution would be to integrate bare chip dies on the substrate. However, this is limited by both the...

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
EIA 0402 ceramic capacitor 1.8 pF	AVX	04025U1R8BAT2A	1 pc
EIA 0402 ceramic capacitor 100 nF	TDK	CGA2B3X7R1H104K050BB	7 pcs
EIA 0402 ceramic capacitor 100 pF	Murata Electronics	GRM1555C1H101JA01D	1 pc
EIA 0402 thick film resistor 10 kΩ	Vishay	CRCW040210K7FKED	1 pc
EIA 0402 ceramic capacitor 10 nF	Murata Electronics	GRM155R71C103KA01D	3 pcs
EIA 0402 ceramic capacitor 10 pF	Murata Electronics	GJM1555C1H100JB01D	3 pc
EIA 0402 ceramic capacitor 12 pF	Murata Electronics	GJM1555C1H120JB01D	2 pcs
EIA 0402 ceramic capacitor 18 pF	KEMET	C0402C180J3GACAUTO	2 pcs
EIA 0402 resistor 1 mΩ	Vishay	MCS04020C1004FE000	2 pcs
EIA 0402 resistor 1 kΩ	Yageo	RC0402FR-071KL	1 pc
EIA 0402 ceramic capacitor 1 nF	Murata Electronics	GRM1555C1H102JA01D	3 pcs
EIA 0603 ceramic capacitor 2.2 uF	Murata Electronics	GCM188R70J225KE22D	2 pcs
EIA 0402 resistor 220 kΩ	Vishay	CRCW0402220KJNED	5 pcs
0805 22 uH inductor	TDK	MLZ2012N220LT000	1 pc
EIA 0402 resistor 330 kΩ	Vishay	CRCW0402330KFKED	1 pc
EIA 0603 ceramic capacitor 4.7 uF	TDK	C1608X6S1C475K080AC	1 pc
EIA 0402 resistor 470 Ω	Vishay	RCG0402470RJNED	1 pc
EIA 0402 resistor 470 kΩ	Vishay	CRCW0402470KJNED	1 pc
EIA 0603 inductor 470 nH	Murata Electronics	LQW18ANR47G00D	1 pc
EIA 0402 resistor 47 kΩ	Murata Electronics	CRCW040247K0JNED	2 pcs
27.0000 MHz crystal 5032	AVX / Kyocera	KC5032A27.0000CMGE00	1 pc
EIA 0402 capacitor 6.8 pF	Murata Electronics	GJM1555C1H6R8CB01D	1 pc
EIA 0402 inductor 82 nH	EPCOS / TDK	B82498F3471J	1 pc
ABS05 32.768 kHz crystal	ABRACON	ABS05-32.768KHZ-T	1 pc
CDBU00340-HF schottky diode	COMCHIP technology	CDBU00340-HF	2 pcs
CG-320S Li-Ion pinpoint battery	Panasonic	CG-320S	1 pc
HSMS282P schottky diode rectifier	Broadcom / Avago	HSMS-282P-TR1G	1 pc
MAX8570 step-up converter	Maxim Integrated	MAX8570EUT+T	1 pc
MICRF113 RF transmitter	Microchip Technology	MICRF113YM6-TR	1 pc
4.3 V Zener diode	ON Semiconductor	MM3Z4V3ST1G	1 pc
OPA237 operational amplifier	Texas Instruments	OPA237N	1 pc
PIC16LF1783 8-bit microcontroller	Microchip Technology	PIC16LF1783-I/ML	1 pc
TPS70628 low-drop regulator	Texas Instruments	TPS70628DBVT	1 pc
EIA 1206 thick film resistor 0 Ω	Yageo	RC1206JR-070RL	2 pcs
EIA 0603 thick film resistor 0 Ω	Yageo	RC0603JR-070RL	1 pc
EIA 0402 thick film resistor 100 kΩ	Yageo	RC0402FR-07100KL	1 pc
EIA 0603 thick film resistor 100 kΩ	Yageo	RC0603FR-07100KL	1 pc
EIA 0805 ceramic capacitor 100 nF	KEMET	C0805C104K5RAC7210	2 pcs
EIA 0402 thick film resistor 10 kΩ	Yageo	RC0402JR-0710KL	1 pc
EIA 1206 ceramic capacitor 10 nF	Samsung	CL31B103KHFSW6E	2 pcs
EIA 0402 thick film resistor 1 kΩ	Yageo	RC0402JR-071KL	2 pcs
EIA 0402 thick film resistor 220 Ω	Yageo	RC0402JR-07220RL	2 pcs
EIA 0402 ceramic capacitor 220 nF	TDK	C1005X5R1C224K050BB	1 pc
EIA 1206 ceramic capacitor 22 nF	TDK	C3216X7R2J223K130AA	2 pcs
SMC B tantalum capacitor 22 uF	AVX	TPSB226K010T0700	1 pc
EIA 0402 thick film resistor 27 Ω	Yageo	RC0402FR-0727RL	2 pcs
EIA 1206 thick film resistor 3.3 Ω	Yageo	RC1206JR-073K3L	3 pcs
SOT23 3.3V zener diode	ON Semiconductor	BZX84C3V3LT1G	1 pc
SMC A tantalum capacitor 4.7uF	KEMET	T491A475M016AT	2 pcs
EIA 0603 thick film resistor 470 Ω	Yageo	RC0603JR-07470RL	2 pcs
EIA 1206 ceramic capacitor 470 nF	KEMET	C1206C471J5GACTU	3 pcs
Electrolytic capacitor 470 uF	Panasonic	EEE-1CA471UP	3 pcs
EIA 0402 ceramic capacitor 47 pF	AVX	04025A470JAT2A	2 pcs
0603 GREEN LED	Lite-On Inc.	LTST-C191KGKT	1 pc
0603 RED LED	Lite-On Inc.	LTST-C191KRKT	1 pc
16 MHz CX3225 crystal	EPSON	FA-238 16.0000MB-C3	1 pc
0805 ferrite bead	Wurth Electronics Inc.	742792040	1 pc
IR2110SO FET driver	Infineon Technologies	IR2110SPBF	1 pc
FT230XS USB to seriál converter	FTDI Ltd.	FT230XS-R	1 pc
Mini USB connector	EDAC Inc.	690-005-299-043	1 pc
PIC16F1783 8-bit microcontroller	Microchip Technology	PIC16F1783-I/ML	1 pc
REG1117 3.3 V regulator SOT223	Texas Instruments	REG1117-3.3/2K5	1 pc
Schottky SMB diode rectifier	STMicroelectronics	STPS3H100UF	1 pc
SMB package TVS diode	Littelfuse Inc.	1KSMBJ6V8	1 pc
IRLZ44NPBF N-channel MOSFET	Infineon Technologies	IRLZ44NPBF	2 pcs
RTL2832U receiver dongle	EVOLVEO	Mars	1 pc
PICkit 3	Microchip Technology	PICkit 3	1 pc
Mini USB to USB A cable	OEM	Mini USB to USB-A	1 pc
Printed circuit board, implantable device	---	Manufacture with the provided supplementary file	1 pc
Printed circuit board, transmitter/receiver device	---	Manufacture with the provided supplementary file	1 pc
Printed circuit board, implantable device	---	Manufacture with the provided supplementary file	1 pc
AWG18 wire	Alpha Wire	3055 BK001	2 m
AWG42 wire	Daburn Electronics	2420/42 BK-100	1 m
Olympus GIFQ-160	Olympus	N/A (part is obsoleted)	1 pc
Single-use electrosurgical knife with knob-shaped tip and integrated jet function	Olympus	KD-655L	1 pc
Single-use oval electrosurgical snare	Olympus	SD-210U-15	1 pc
15.5 mm lens hood	FujiFilm	DH-28GR	1 pc
Injection therapy needle catheter	Boston Scientific	25G	1 pc
Alligator law grasping forceps	Olympus	FG-6L-1	1 pc
Instant Mix 5 min epoxy	Loctite	N/A	1 pc
Heat shrinkable tubing, inside diameter 9.5 mm	TE Connectivity	RNF-100-3/8-X-STK	1 pc
ChipQuik solder paste	Chip Quik	SMD4300AX10	1 pc