Wirelessly Powered Electrical Stimulation System and Related Methods

Abstract

A system, device, and related implant method for a wirelessly rechargeable electrical stimulation device are generally provided. A typical system includes a wearable transmitter for wireless power transmission and an implantable electrical stimulation device. Specifically, the electrical stimulation device includes a power management module, a pulse generator, and one or more electrodes. In some embodiments, the electrical stimulation device may include a microcontroller and some sensors for detecting related physiological signals of the target muscle group for closed-loop electrotherapy. Further, a minimally invasive implant procedure for electrotherapy through a natural opening such as the gastrointestinal tract is also disclosed. In some embodiments, the electrical stimulation is applied continuously to restore the normal function of the target muscle group.

Description

Technical Field

[0001] The present invention generally relates to a wirelessly powered medical device for minimally invasive electrical stimulation therapy to restore the normal function of typical muscle groups such as the gastrointestinal tract.

Background Art

[0002] Functional electrical stimulation (FES), a method of using electrical stimulation to restore the degenerated function of typical muscle groups, is commonly used clinically. Various systems, sensors, and algorithms have been investigated to improve clinical effectiveness. Transcutaneous electrical stimulation is a non-invasive method but requires high voltage or high current to apply effective stimulation across the skin. On the other hand, implantable stimulation devices apply direct electrical pulses to control the target muscle group. However, the operating time of implantable devices is limited by the battery capacity, which is directly related to the battery size. Large and rigid batteries require invasive implantation with large incisions, while small batteries require frequent replacement, which would increase the risk of infection and other side effects.

[0003] Wireless power transmission is a promising solution for implantable medical devices and avoids the above-mentioned drawbacks. However, the efficiency of wireless power transmission strongly depends on the coupling coefficient related to the orientation, position, and geometric configuration of the receiving coil and the transmitting coil. Furthermore, efficient power transmission through deep tissues remains difficult because the magnetic field strength rapidly decays as the distance increases.

[0004] This specification provides a system, device, and related implantation procedure for wireless electrical stimulation. In one aspect, the invention includes a wearable power transmitter for wireless power transmission in daily operations. In one aspect, the invention includes an implantable electrical stimulation device that is wirelessly powered or wirelessly charged based on magnetic resonance coupling, extends battery life, and eliminates the need for battery replacement and related potential risks. In some embodiments, the electrical stimulation device includes a microcontroller and several sensors for closed-loop electrical stimulation therapy. In one aspect, a minimally invasive implantation method is also disclosed. In some embodiments, an endoscopic implantation procedure through a natural orifice is provided. This avoids invasive surgery for implantation and thus reduces the risk of infection during recovery. SUMMARY OF THE INVENTION

[0005] A system, device, material, and related implantation method for a wireless electrical stimulation system are disclosed. The system consists of a wearable power transmitter for wireless power transmission and an implantable electrical stimulation device having a receiving coil. The transmitting coil is disposed outside the body and generates an alternating magnetic field for wireless power transmission through deep tissue. The electrical stimulation device includes a receiving coil, a power management module, a pulse generator, and one or more pairs of electrodes. In some embodiments, the electrical stimulation device further includes a sensor for detecting relevant physiological signals of a target group and a microcontroller for data processing and wireless communication. Additionally, a related minimally invasive delivery method is provided. The electrical stimulation device is delivered through a natural orifice by endoscopy without the need for invasive therapy or implanted into the abdominal cavity through a laparotomy with an incision less than 15 mm.

[0006] In one aspect, a wearable power transmitter is provided. Generally, the power transmitter includes a transmitting coil driven by an alternating current or voltage generated by a portable control board. Based on Faraday's law, the transmitting coil generates an alternating magnetic field. Further, the transmitting coil is matched with a capacitor operating at a resonance frequency in the range of 100 kHz to 1 GHz. In some embodiments, the input power and operating frequency of the transmitting coil are controlled by a portable control box. The control box has a rechargeable battery, and the power source generates a constant current that is converted to an alternating current by a full-bridge inverter. Its switching frequency determines the operating frequency controlled by a rectangular wave signal generated by a control circuit. And the strength of the magnetic field shows a linear relationship with the driving current.

[0007] In some embodiments, to achieve maximum efficiency, the transmitting coil is operated at a frequency having a peak quality factor mainly related to the geometric configuration of the transmitting coil. In some embodiments, the transmitting coil is configured in a pair of solenoid shapes that generate a strong and uniform magnetic field within the area surrounded by the coil. In some embodiments, the coil is a pair of Helmholtz coils. In some embodiments, the coil is woven into a planar pad, and its magnetic field rapidly decays as the distance increases.

[0008] In some embodiments, the transmitting coil operates at a fixed frequency within the industrial, scientific, and medical (ISM) radio band. The signal generator generates an alternating voltage having the operating frequency, and the input power is controlled by a power amplifier. To achieve maximum power transmission efficiency, the impedance of the power transmitter is adjusted to reduce the amount of reflection attenuation caused by impedance mismatch. In some embodiments, an antenna tuner consisting of a set of capacitors and inductors is implemented to automatically adjust the impedance of the transmitting coil.

[0009] In one aspect, an implantable electrical stimulation device is provided. It includes a receiving coil that surrounds a closed area. While an alternating magnetic field is transmitted through a closed loop, an alternating voltage is induced in the receiving coil. Subsequently, the alternating voltage is converted to a direct current voltage by a full-bridge rectifier. Then, a voltage with high amplitude and noise is regulated to a stable voltage by a power management module. Finally, a pulse generator generates voltage pulses with programmable frequency, amplitude, and pulse width. In some embodiments, a constant current module follows the pulse generator. This converts the voltage pulses to current pulses with a constant amplitude while applied to various loads. In some embodiments, the electrical stimulation device may also include on-board antenna operation and a microcontroller unit (MCU) to set these parameters by a wireless communication module.

[0010] In some embodiments, the electrical stimulation device includes sensors that detect physiological signals related to the target muscle group, including but not limited to electromyogram examinations related to the electrical activity of the muscle group, pressure sensors, and strain sensors related to the motility of the target muscle.

[0011] In some embodiments, a closed-loop stimulation algorithm is executed. Specifically, the microcontroller periodically measures the physiological signals of the target muscle group by sensors. When an abnormal signal is detected, the microcontroller generates an electrical pulse train for a typical period to restore the normal function of the muscle group. When the physiological signal returns to a normal value, the microcontroller terminates the electrical stimulation.

[0012] In some embodiments, the power management module includes a full-bridge rectifier and a linear low-dropout regulator (LDO). In some embodiments, the power management module further includes an inverter converter that generates a negative voltage for the pulse generator to synthesize a biphasic stimulation signal. In some embodiments, the power management module may further include a buck converter for more efficient power management.

[0013] Generally, a method of fabricating an electrode is provided. In some embodiments, the electrode is fabricated in the form of a microneedle that penetrates tissue. In some embodiments, the electrode is a planar metal plate made of platinum, gold, iridium, etc. In some embodiments, the surface of the electrode is modified by electrodeposition to improve their charge injection ability, anti-biofouling ability, and biocompatibility.

[0014] A method of fabricating a wireless electrical stimulation device and a receiving coil is disclosed. To adapt to the movement of the target muscle during electrical stimulation, the wireless electrical stimulation device is fabricated on a flexible substrate such as PDMS, PI, PET, PU, etc. In some embodiments, the circuit traces are fabricated by conductive materials including, but not limited to, eutectic gallium and indium (EGaIn), and copper. In some embodiments, the device is encapsulated by a coating material having good biocompatibility and waterproofness such as parylene.

[0015] In one aspect, a minimally invasive implantation method and related uses are provided. Natural orifices such as the gastrointestinal tract, urinary tract, etc. are accessible by endoscopy, which provides a minimally invasive method for the implantation or delivery of an electrical stimulation device.

[0016] In some embodiments, a tunnel is formed between the mucosal layer and the muscular layer of the gastrointestinal tract. Thereafter, the wireless electrical stimulation device is implanted through the tunnel. Thereafter, the tunnel is sutured or closed by several endoclips.

[0017] In some embodiments, the electrical stimulation device is integrated with a medical device such as a stent. They are delivered through a natural orifice by a thin catheter. After the stent is released, the electrical stimulation device is retained inside the body lumen for a duration.

[0018] In some embodiments, the electrical stimulation device is applied to the gastrointestinal tract to regulate GI disorders such as irritable bowel disease, gastroesophageal reflux disease, or fecal incontinence.

[0019] In some embodiments, the electrical stimulation device is used in the bladder or urinary tract to manage urinary incontinence.

[0020] In some embodiments, the electrical stimulation device is used to restore the normal function of the pelvic floor muscles. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Non-limiting embodiments of the present invention are illustrated by examples in combination with figures that are schematic and not intended to be drawn to scale. In the drawings, the same or substantially the same components shown are typically represented by a single number. For clarity, not every component in every figure is labeled, nor are all components of each embodiment of the present invention shown where illustration is not necessary for one of ordinary skill in the art to understand the present invention.

[0022]

Figure 1

Figure 2a

Figure 2b

Figure 2c

Figure 3a

Figure 3b

Figure 4a

Figure 4b

Figure 5a

Figure 5b

Figure 6

Figure 7a

Figure 7b

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13a

Figure 13b

Figure 14a

Figure 14b

Figure 14c

Figure 15a

Figure 15b

Figure 16

Figure 17

Figure 18

DETAILED DESCRIPTION OF THE INVENTION

[0023] The present invention provides a system for wireless electrical stimulation. In one embodiment, the system includes: i) a portable control board, and ii) a wearable power transmitter including a transmission coil for generating an alternating magnetic field having an operating frequency in the range of 100 kHz to 1 GHz for wireless power transmission, and an implantable wireless electrical stimulation device including: i) one or more receiving coils for receiving the alternating magnetic field from the wearable power transmitter and generating an alternating voltage, ii) a power management module for rectifying the alternating voltage to provide a stable voltage in the range of -15 V to 15 V, iii) a pulse generator for generating a current pulse signal having programmable amplitude, frequency, and pulse width, iv) one or more electrodes configured to contact a target muscle group to deliver the current pulse signal, and v) a microcontroller for data processing and wireless communication.

[0024] In one embodiment, the portable control board includes a control circuit including: i) a rechargeable battery, ii) a power management circuit providing a constant current in the range of 0.1 A to 3 A and different voltages including 5 V and 15 V, iii) a rectangular wave signal generator having a frequency in the range of 100 kHz to 1 MHz, a metal oxide semiconductor field effect transistor (MOSFET) driver, a full bridge inverter composed of four MOSFETs, and one or more matching capacitors.

[0025] In one embodiment, the portable control board includes: i) a rechargeable battery, ii) a power management circuit, iii) a signal generator for generating an alternating signal having a frequency in the range of 1 MHz to 1 GHz, iv) a power amplifier configured with an output power in the range of 1 watt to 20 watts, and v) an antenna tuner including a set of capacitors and inductors that automatically minimizes the reflection attenuation of the transmission coil at the operating frequency.

[0026] In one embodiment, the geometric configuration of the transmission coil includes a planar Helmholtz pair having a diameter in the range of 5 cm to 80 cm, a single solenoid, or a pair of solenoids.

[0027] In one embodiment, the implantable wireless electrical stimulation device further includes a wireless charging circuit having a charging current in the range of 5 mA to 100 mA, and a rechargeable battery having a diameter of less than 15 mm, a thickness of less than 10 mm, and a capacity in the range of 5 mAh to 200 mAh.

[0028] In one embodiment, the implantable wireless electrical stimulation device further includes a sensor for detecting one or more physiological signals selected from the group consisting of compression, tension, and electromyogram signals of a target muscle group.

[0029] In one embodiment, the frequency of the current pulse signal is in the range of 1 Hz to 1 kHz.

[0030] In one embodiment, the amplitude of the current pulse signal is in the range of 3 mA to 15 mA.

[0031] In one embodiment, the pulse width of the current pulse signal is in the range of 100 microseconds to 200 milliseconds.

[0032] In one embodiment, the receiving coil is made of a single-strand conductive wire, and the single-strand conductive wire is made of i) a material selected from the group consisting of copper, gold, platinum, and nitinol alloy, or ii) a silicone tube filled with liquid metal.

[0033] In one embodiment, the liquid metal is gallium-indium eutectic (EGaIn).

[0034] In one embodiment, the receiving coil is fabricated in the form of a stent having a stretchability in the range of 50% to 200%, a diameter in the range of 16 mm to 28 mm, and a length in the range of 80 mm to 120 mm.

[0035] In one embodiment, the receiving coil includes a ferrite core having a relative permeability in the range of 500 to 300, and is configured in a miniaturized size with a length of less than 10 mm and a diameter of less than 10 mm.

[0036] In one embodiment, the receiving coil is configured in a planar shape with a length of less than 100 mm and a width of less than 50 mm.

[0037] In one embodiment, the electrode is fabricated in a needle shape with a length in the range of 100 micrometers to 1 mm and is configured in a shape including a cone, a prism, or a spine.

[0038] In one embodiment, the electrode is fabricated from a conductive material including copper, and the surface of the electrode is modified by gold, platinum, and iridium oxide.

[0039] In one embodiment, the wireless electrical stimulation device is made of a soft material including polydimethylsiloxane (PDMS), styrene ethylene butylene styrene (SEBS), polyurethane (PU), or hydrogel as a base material and an encapsulant, and a novel conductive material including one or more of silver nanowires, carbon nanotubes, gold nanowires, poly(3,4-ethylenedioxythiophene) polystyrene sulfonic acid (PEDOT:PSS), or EGaIn.

[0040] In one embodiment, the present invention further provides an algorithm for closed-loop electrical stimulation therapy executed in a microcontroller of the wireless electrical stimulation device. When the sensor detects an abnormal physiological signal, the microcontroller starts electrical stimulation, and when the physiological signal returns to a normal value, the electrical stimulation is terminated after a period of at least 20 minutes.

[0041] In one embodiment, the present invention further provides a minimally invasive method assisted by an endoscope through a natural orifice for implanting the system of the present invention into a tissue having a mucosal layer, a muscular layer, and a submucosal layer. The implantation procedure includes: (a) creating a submucosal tunnel by incising the mucosal layer with an incision of less than 15 mm; (b) implanting the wireless electrical stimulation device into the submucosal tunnel between the muscular layer and the submucosal layer; and (c) closing the submucosal tunnel with a set of clips that automatically separate after a period of less than 10 days.

[0042] In one embodiment, the endoscope passing through the natural orifice is for the gastrointestinal tract.

[0043] In one embodiment, the present invention provides a minimally invasive method for implanting the system of the present invention, wherein the receiving coil is fabricated in the form of a stent and delivered through a natural orifice by a delivery device including a flexible shell, a flexible tip, a block ring, and a balloon catheter. The implantation procedure includes: (a) stretching a radioelectric stimulation device onto the stent and inserting it into the delivery device; (b) inserting the delivery device for delivering the implantable radioelectric stimulation device through the natural orifice; (c) releasing the electric stimulation device integrated onto the stent by pulling the flexible shell of the delivery device; (d) inserting the electrodes of the radioelectric stimulation device through the mucosal layer and into the muscle tissue by inflating the balloon catheter of the delivery device; and (e) deflating the balloon catheter and retracting the delivery device through the natural orifice.

[0044] In one embodiment, the present invention provides a minimally invasive method for implanting the system of the present invention into the abdominal cavity by laparoscopy. The implantation procedure includes: (a) incising the abdominal cavity through an incision less than 15 mm; (b) contacting the electrodes of the radioelectric stimulation device with the target muscle group; and (c) fixing the radioelectric stimulation device with a set of surgical sutures and closing the abdominal cavity with a series of surgical sutures.

[0045] In one embodiment, the target muscle group includes the lower esophageal sphincter, the anal sphincter, or the gastric fundus.

[0046] The present invention will be better understood by reference to the following detailed experiments. Those skilled in the art will readily understand that the specific experiments described are for illustrative purposes only and are not meant to limit the invention described herein, which is defined by the claims that follow.

[0047] Throughout this application, various references or publications are cited. The disclosures of these references or publications are hereby incorporated by reference in their entirety to more fully describe the state of the art to which the present invention pertains. It should be noted that the transitional term "comprising", which is synonymous with "including", "containing", or "characterized by", is inclusive or non-limiting and does not exclude additional, unrecited elements or method steps.

[0048] The present invention provides a wireless electrical stimulation system for long-term in vivo electrical stimulation therapy. Referring to FIG. 1, the present invention includes two components: a wearable transmitter having a portable control board for wireless power transmission, and a wireless electrical stimulation device that applies electrical pulses to restore the normal function of a target muscle group. Alternating current flows through a transmitting coil that generates an alternating magnetic field. However, the intensity of the magnetic field generated by a planar coil rapidly decays as the distance increases. Furthermore, the geometric configuration of the transmitting coil greatly affects the feasibility of in vivo wireless power transmission. Therefore, a transmitting coil with a proper configuration is important for wireless power transmission in deep tissues.

Example

[0049] Example 1 Typical Design of a Wearable Power Transmitter Referring to FIG. 2a, the transmitting coil is a pair of solenoid coils braided by a single conductive wire including but not limited to copper wire. In some embodiments, the transmitting coil has a diameter in the range of 30 cm to 80 cm, which can accommodate various body shapes. Each side of the solenoid has an equal number of turns in the range of 5 turns to 40 turns. The distance between the two solenoids is equal to the radius of the power transmitter. Referring to FIG. 2b, this geometric configuration generates a uniform and relatively strong magnetic field within the coil, which is essential for powering devices embedded within deep tissues.

[0050] For daily operations, the power transmission coil is fabricated in the form of a jacket or a wearable connection. In some embodiments, the power transmission coil is fabricated on a rigid substrate to avoid shape changes, including but not limited to a polyvinyl chloride (PVC) tube and a 3D printed polylactic acid (PLA) shell. In some embodiments, the transmission coil is configured in an elliptical shape to accommodate various body shapes.

[0051] The input power of the transmission coil is mainly limited by the specific absorption rate (SAR), which is a safety evaluation criterion for wireless power transmission. To minimize the power loss due to the internal impedance of the transmission coil, the power transmitter is operated near a frequency having a peak quality factor related to the geometric configuration of the power transmitter. Referring to Figure 2c, the peak quality factor is found by sweeping the frequencies within the operating range.

[0052] Example 2 Typical Design of a Portable Control Board Referring to Figure 3a, the portable control board includes a rechargeable battery, a power management module, a control circuit, and an adjustable matching capacitor. The control circuit includes a pulse width modulation (PWM) generator that provides a rectangular wave signal having an adjustable frequency in the range of 100 kHz to 1 MHz, controls the switching frequency of the full-bridge inverter, and the full-bridge inverter converts direct current into alternating current and then drives the transmission coil. To achieve high power transmission efficiency, the transmission coil is matched to the operating frequency having a peak quality factor by adjusting the matching capacitor. Further, the magnetic field shows a linear relationship with the drive current. The input power is adjusted by controlling a constant current flow to the full-bridge inverter. Referring to Figure 3b, a typical prototype of the control board is disclosed. This includes a rechargeable battery that can supply power to the system for a duration exceeding 8 to 24 hours depending on the drive current. In some embodiments, a large adjustable capacitor can be replaced with a series of built-in capacitors to minimize the overall size of the control board.

[0053] Embodiment 3 Design alternative of the power transmitter In some embodiments, the transmission coil has a planar shape matched to a resonance frequency in the range of 1 MHz to 100 MHz. Referring to FIG. 4a, this is configured in the form of a coplanar concentric coil braided by a single conductive wire. Referring to FIG. 4b, the magnetic field generated by this planar coil decreases as the distance from the center point increases. In some embodiments, the transmission coil has an outer diameter in the range of 10 cm to 50 cm. In some embodiments, the transmission coil is arranged parallel to the chest of the subject. In some embodiments, the subject is located at the center of the transmission coil.

[0054] Despite various geometric configurations, this planar coil is matched to a typical resonance frequency such as 13.56 MHz. A corresponding drive circuit is disclosed. Referring to FIG. 5a, the drive circuit includes a rechargeable battery, a signal generator that supplies an AC voltage signal at the resonance frequency, and a power amplifier that amplifies the input voltage to the transmission coil. Referring to FIG. 5b, a typical prototype is disclosed. This circuit operates at a fixed frequency and fixed input power, but provides a lightweight and compact form factor. Furthermore, since the resonance frequency will drift due to parasitic capacitance, the transmission coil is susceptible to environmental influences. In some embodiments, the antenna tuner consists of a reflection bridge and a set of capacitors and inductors. This automatically adjusts the impedance of the transmission coil to minimize power loss due to resonance frequency drift.

[0055] Embodiment 4 General design of an implantable wireless electrical stimulation device Referring to FIG. 6, the wireless electrical stimulation device may generally include three components, namely, a power management module, a stimulation module, and further, a sensing module. In some embodiments, the wireless electrical stimulation device is completely wirelessly powered and requires continuous operation of a wearable power transmitter. The power management module includes a power management integrated circuit (IC) and a receiving coil. The receiving coil induces an alternating voltage within a time-varying magnetic field. In some embodiments, the alternating voltage is converted to a direct current voltage by a rectifier circuit such as, but not limited to, a full-bridge converter. The converted voltage is smoothed by a capacitor. Further, a linear low-dropout regulator (LDO) adjusts the voltage to a stable voltage. In some embodiments, an inverter converter generates a negative voltage for the stimulation module to generate biphasic stimulation. In some embodiments, the wireless electrical stimulation device is battery-powered and wirelessly charged. The power management module further includes a rechargeable battery and related charging circuits. In some embodiments, the wireless electrical stimulation device includes a rechargeable battery that can be wirelessly recharged. This has a capacity in the range of 1 mAh to 2000 mAh and supplies power to the entire circuit over a typical period in the range of 5 minutes to 24 hours. On the other hand, the battery capacity is directly related to the battery size. In some embodiments, the rechargeable battery has a thickness of less than 6 mm and a diameter of less than 12 mm. In some embodiments, the wireless charging circuit has a charging current in the range of 5 mA to 400 mA.

[0056] In some embodiments, the sensing module includes electrodes for measuring the electromyogram of the target muscle group. In some embodiments, the sensing module includes a pressure sensor for measuring the intracavity pressure. In some embodiments, the sensing module includes a strain sensor for directly measuring muscle movement. In some embodiments, the stimulation device also includes a wireless communication module including a microcontroller and an antenna for data processing and wireless communication.

[0057] Generally, a pulse train consists of a series of pulse signals having a constant interval and pulse width. In some embodiments, the stimulation signal is a voltage pulse. It applies a pulse having a constant voltage amplitude to the tissue. Due to the parasitic capacitance between the tissue electrodes, the charging current changes during stimulation. Overcharging has associated safety issues. Referring to FIG. 7, in some embodiments, the stimulation module includes a constant current module that converts a voltage pulse into a constant current pulse having different loads in the range of 3 mA to 10 mA. In some embodiments, the pulse is a single-phase signal. However, the accumulated charge can lead to muscle fatigue and electrode damage. Referring to FIG. 7b, to achieve a net zero current, charge-balanced stimulation is implemented by a biphasic current pulse.

[0058] According to previous studies, all of the amplitude, frequency, and pulse width affect the effectiveness of electrostimulation therapy. Referring to FIG. 8, the frequency is controlled by a voltage signal generated by a microcontroller in the range of 1 Hz to 1000 Hz. The pulse width is programmable from 50 microseconds to 500 milliseconds. In combination with a wireless communication module, all stimulation parameters can be programmed wirelessly.

[0059] Example 5 Method for fabricating a wireless electrostimulation device In one aspect, a method of fabricating a wireless electrical stimulation device is disclosed. To accommodate muscle movement during stimulation, the wireless electrical stimulation device is fabricated with a flexible form factor. Referring to FIG. 9, in some embodiments, the circuit is fabricated on a flexible substrate such as polyimide by a conventional flexible PCB method. Referring to FIG. 10, in some embodiments, the circuit is further fabricated on a stretchable substrate including, but not limited to, polydimethylsiloxane (PDMS), polyurethane (PU), and styrene ethylene butylene styrene (SEBS). The insulator layer has a thickness in the range of 10 micrometers to 500 micrometers. Thereafter, a conductive layer is deposited on the insulator layer. The material of the conductive layer includes, but is not limited to, copper, gold, titanium, platinum, and chromium. The film thickness of the conductive layer is in the range of 50 nm to 200 nm. In some embodiments, an EGaIn solution containing 3 wt% NaOH is poured onto the conductive layer to form an alloy with inherent stretchability. A laser is used to etch away redundant portions to form circuit traces. In some embodiments, the wavelength of the laser is in the range of 355 nm to 1064 nm. The fabricated line width is greater than at least 10 micrometers. After cleaning and drying, electronic components are carefully placed on the EGaIn traces. Finally, the entire circuit is encapsulated with an insulating material such as PDMS and parylene. Referring to FIG. 11, the large surface tension of EGaIn provides additional force to ensure stable electrical contact between the components and the circuit traces. Referring to FIG. 12, the fabricated circuit can undergo various deformations, including bending, twisting, and stretching, which are suitable for applications involving muscle movement.

[0060] In one aspect, a method of fabricating a receiving coil is disclosed. Generally, receiving coils have two types including an air-core coil as shown in FIG. 13a and a ferrite-core coil as shown in FIG. 13b. In some embodiments, the air-core coil is fabricated in the form of a planar coil on a flexible or stretchable substrate as described above. Referring to FIG. 14a, in some embodiments, the air-core coil is braided by a single-wire conductive coil in the form of a stent. The conductive material includes, but is not limited to, a nitinol alloy covered with an insulating layer. Referring to FIG. 14b, in some embodiments, the air-core coil is braided by a single-wire conductive coil along the skeleton of the stent. The conductive material includes, but is not limited to, a silicone tube filled with EGaIn. Referring to FIG. 14c, excellent mechanical properties and parallel meshes jointly enable good stretchability of the air-core coil that adapts to various deformations in the body. In some embodiments, the receiving coil includes a ferrite core having a high relative permeability. This provides a smaller size to achieve the same voltage. In some embodiments, the receiving coil has a diameter in the range of 4 mm to 10 mm and a length in the range of 2 mm to 10 mm. In some embodiments, the receiving coil is tuned to a resonance frequency in the range of 1 MHz to 100 MHz.

[0061] Example 6 Non-invasive Oral Delivery of a Radioelectric Stimulation Device In one aspect, non-invasive endoscopic delivery through a natural orifice is provided. In some embodiments, the wireless electrical stimulation device, referring to FIG. 15a, is integrated onto the stent. This exhibits good mechanical properties with stretchability up to 50%. Referring to FIG. 15b, the stent with the electrical stimulation device is compressed within the delivery catheter. The catheter is then delivered through the natural orifice. After the stent is released, the self-expanding stent structure helps the device to be retained inside the narrow channel. Finally, the balloon catheter is inflated to fully release the wireless electrical stimulation device and bring the electrodes into firm contact with the tissue. In some embodiments, the electrodes are fabricated in the form of micro-needles and are then inserted across the mucosal layer, with the needle tip contacting the muscle layer. The length of the micro-needles ranges from 300 um to 800 um. The diameter of the micro-needles ranges from 100 um to 600 um. In some embodiments, the electrodes are attached onto the outer layer of the stent. Since the stent applies a perpendicular force to the tissue, the stent is in direct contact with the tissue.

[0062] Referring to FIG. 16, a delivery catheter for non-invasive endoscopic delivery is provided. The delivery catheter generally consists of a balloon catheter, a soft tip, a block ring, and a flexible shell. The stent is compressed and loaded between the flexible tube and the cover tube. During the surgery, the surgeon holds the distal end of the flexible tube and pulls the cover tube to release the stent. The block ring prevents the stent from retracting due to friction during the release process. In some embodiments, the procedure is performed under X-ray. The X-ray marker indicates the position of the stent under the X-ray image. In some embodiments, the delivery catheter includes a small camera located at the head of the flexible tip. Due to the illumination of the LED array around the camera, it provides an endoscopic view for the operation, avoids exposure to ionizing radiation, and increases the success rate of the delivery procedure in a dark in-vivo environment.

[0063] Example 6 Low-invasive Implantation Method of a Wireless Rechargeable Electrical Stimulation Device In one aspect, endoscopic procedures for minimally invasive implantation are also disclosed. In some embodiments, the radioelectrical stimulation device is implanted through a natural opening including, but not limited to, the gastrointestinal (GI) tract. Referring to FIG. 17, the endoscope is inserted through the esophagus. An initial incision is made to form a tunnel between the mucosal layer and the muscular layer. Then, the electrical stimulation device is delivered and implanted within the tunnel. The exposed electrodes are in direct contact with the esophageal muscle for effective electrical stimulation. At the end of the procedure, the incision is closed with endoscopic clips. After a period of five days, the endoscopic clips are automatically removed by tissue regeneration.

[0064] In some embodiments, the radioelectrical stimulation device is implanted intraperitoneally by laparoscopy. The peritoneal cavity is opened with an incision less than 15 mm. Also, the electrodes of the radioelectrical stimulation device are configured to contact a target muscle group including, but not limited to, the lower esophageal sphincter, the anal sphincter, and the gastric fundus. Finally, the radioelectrical stimulation device is fixed by a set of surgical sutures, and the peritoneal cavity is sealed with a series of surgical sutures.

[0065] Example 7 Algorithm for Closed-Loop Electrical Stimulation Therapy Referring to FIG. 18, a closed-loop electrical stimulation algorithm is implemented in a microcontroller. When an abnormal signal is detected, the microcontroller starts electrical stimulation pulses over a period of time to restore the normal function of the target muscle group. The electrical stimulation session stops after the physiological signal returns to normal values. In some embodiments, the detected signal is sent by a wireless communication module for further analysis. In some embodiments, the implanted sensor and this algorithm automatically control the electrical stimulation without intervention.

[0066] In some embodiments, the electrical stimulation device is implanted in the lower esophageal sphincter for the treatment of GERD. In some embodiments, the electrical stimulation device is implanted near the anal sphincter for the treatment of fecal incontinence. In some embodiments, the electrical stimulation device is delivered through the urinary tract and implanted in the bladder for the treatment of urinary incontinence. The physiological signal refers to the pressure at the target site measured by the pressure sensor. When the pressure falls below the threshold, the microcontroller starts an electrical stimulation session to return the pressure to the normal value.

[0067] In some embodiments, the electrical stimulation device is implanted in the stomach for the treatment of gastroparesis. The strain sensor is disposed and fixed at the fundus of the stomach. When the stomach is full, the fundus of the stomach is stretched due to the volume change. After detecting a strain change exceeding the threshold, the wireless electrical stimulation device starts an electrical stimulation period. This causes the movement of the stomach to assist in food digestion. The microcontroller stops the stimulation when the strain value returns to the normal value, indicating that the stomach is empty.

[0068] Related uses for wireless electrical stimulation systems and minimally invasive implantation procedures are also provided. Natural orifices include, but are not limited to, the gastrointestinal tract, urinary tract, trachea, vagina, and the like. In some embodiments, the electrical stimulation device is implanted in the small intestine for the treatment of irritable bowel disease. In some embodiments, the electrical stimulation device is implanted to restore the normal function of the pelvic floor muscles. In some embodiments, the physiological signal refers to the electromyogram measured by one or more electrodes.

Claims

1. A system for wireless electrical stimulation, comprising: i. A portable control board, and ii. A transmitting coil for generating an alternating magnetic field having an operating frequency in the range of 100 kHz to 1 GHz for wireless power transfer A wearable power transmitter including; i. One or more receiving coils for receiving the alternating magnetic field from the wearable power transmitter and generating an alternating voltage; ii. A power management module for rectifying the alternating voltage to provide a stable voltage in the range of -15V to 15V; iii. A pulse generator for generating a current pulse signal having a programmable amplitude, frequency, and pulse width; iv. One or more electrodes configured to contact a target muscle group to deliver the current pulse signal; and v. A microcontroller for data processing and wireless communication An implantable wireless electrical stimulation device including; A system for wireless electrical stimulation.

2. The portable control board includes: i. A rechargeable battery; ii. A power management circuit providing a constant current in the range of 0.1A to 3A and different voltages including 5V and 15V; iii. A control circuit including a rectangular wave signal generator having a frequency in the range of 100 kHz to 1 MHz, a metal oxide semiconductor field effect transistor (MOSFET) driver, a full-bridge inverter composed of four MOSFETs, and one or more matching capacitors The system according to claim 1.

3. The portable control board includes: i. A rechargeable battery; ii. A power management circuit; iii. A signal generator for generating an alternating signal having a frequency in the range of 1 MHz to 1 GHz; iv. A power amplifier configured with an output power in the range of 1 watt to 20 watts; v. An antenna tuner including a set of capacitors and inductors for automatically minimizing the reflection attenuation of the transmitting coil at the operating frequency The system according to claim 1.

4. The system according to claim 1, wherein the geometric configuration of the transmitting coil includes a planar Helmholtz pair, a single solenoid, or a pair of solenoids having a diameter in the range of 5 cm to 80 cm.

5. The system according to claim 1, wherein the implantable wireless electrical stimulation device further includes a wireless charging circuit having a charging current in the range of 5 mA to 100 mA, and a rechargeable battery having a diameter of less than 15 mm, a thickness of less than 10 mm, and a capacity in the range of 5 mAh to 200 mAh.

6. The system according to claim 1, wherein the implantable wireless electrical stimulation device further includes a sensor for detecting one or more physiological signals selected from the group consisting of compression, tension, and electromyogram signals of a target muscle group.

7. The system according to claim 1, wherein the frequency of the current pulse signal ranges from 1 Hz to 1 kHz.

8. The system according to claim 1, wherein the amplitude of the current pulse signal ranges from 3 mA to 15 mA.

9. The system according to claim 1, wherein the pulse width of the current pulse signal ranges from 100 microseconds to 200 milliseconds.

10. The receiving coil is made of a single-strand conductive wire, and the single-strand conductive wire is i. a material selected from the group consisting of copper, gold, platinum, and nitinol alloy, or ii. a silicone tube filled with liquid metal The system according to claim 1.

11. The system according to claim 10, wherein the liquid metal is gallium-indium eutectic (EGaIn).

12. The system according to claim 1, wherein the receiving coil is fabricated in the form of a stent having a stretchability in the range of 50% to 200%, a diameter in the range of 16 mm to 28 mm, and a length in the range of 80 mm to 120 mm.

13. The system according to claim 1, wherein the receiving coil includes a ferrite core having a relative permeability in the range of 500 to 300 and is configured in a miniaturized size with a length of less than 10 mm and a diameter of less than 10 mm.

14. The system according to claim 1, wherein the receiving coil is configured in a planar shape with a length of less than 100 mm and a width of less than 50 mm.

15. The system according to claim 1, wherein the electrode is fabricated in a needle shape with a length in the range of 100 micrometers to 1 mm and is configured in a shape including a cone, prisms, or spines.

16. The system according to claim 1, wherein the electrode is made of a conductive material containing copper, and the surface of the electrode is modified by gold, platinum, and iridium oxide.

17. The system according to claim 1, wherein the wireless electrical stimulation device is made of a soft material including polydimethylsiloxane (PDMS), styrene ethylene butylene styrene (SEBS), polyurethane (PU), or hydrogel as a base material and a encapsulated material, and a novel conductive material including one or more of silver nanowires, carbon nanotubes, gold nanowires, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), or EGaIn.

18. An algorithm for closed-loop electrical stimulation therapy executed in a microcontroller of a wireless electrical stimulation device, wherein when a sensor detects an abnormal physiological signal, the microcontroller starts electrical stimulation, and when the physiological signal returns to a normal value, the electrical stimulation is terminated after a period of at least 20 minutes.

19. A minimally invasive method assisted by endoscopy through a natural orifice for implanting the system according to claim 1 into a tissue having a mucosal layer, a muscular layer, and a submucosal layer, the implanting procedure comprising: (a) creating a submucosal tunnel by incising the mucosal layer with an incision less than 15 mm; (b) implanting the wireless electrical stimulation device into the submucosal tunnel between the muscular layer and the submucosal layer; (c) closing the submucosal tunnel with a set of clips that automatically separate after a period of less than 10 days and including.

20. The method according to claim 19, wherein the endoscopy through the natural orifice is for the gastrointestinal tract.

21. A minimally invasive method for implanting the system according to claim 1, wherein the receiving coil is fabricated in the form of a stent and is delivered through a natural orifice by a delivery device including a flexible shell, a flexible tip, a block ring, and a balloon catheter, the implanting procedure comprising: (a) stretching the wireless electrical stimulation device onto the stent and inserting it into the delivery device; (b) inserting the delivery device for delivering the implantable wireless electrical stimulation device through the natural orifice; (c) releasing the electrical stimulation device integrated on the stent by pulling the flexible shell of the delivery device; (d) inserting the electrodes of the wireless electrical stimulation device through the mucosal layer and into the muscle tissue by inflating the balloon catheter of the delivery device. (e)a step of evacuating the air from the balloon catheter and retracting the delivery instrument through the natural opening A method comprising the above steps.

22. A minimally invasive method for implanting the system according to claim 1 into the abdominal cavity by laparoscopic surgery, wherein the implantation procedure comprises (a)a step of incising the abdominal cavity with an incision less than 15 mm; (b)a step of bringing the electrodes of the radioelectrical stimulation device into contact with the target muscle group; (c)fixing the radioelectrical stimulation device with a set of surgical sutures and closing the abdominal cavity with a series of surgical sutures A method comprising the above steps.

23. The method according to claim 22, wherein the target muscle group includes the lower esophageal sphincter, the anal sphincter, or the gastric fundus.

Images