Bioelectronics for mapping gut activity

Deployment of an electrocorticography system with a soft robotic actuator

Electrocorticography (ECoG) is a minimally invasive approach frequently used clinically to map epileptogenic regions of the brain and facilitate lesion resection surgery and increasingly explored in brain-machine interface applications. Current devices display limitations that require trade-offs among cortical surface coverage, spatial electrode resolution, aesthetic, and risk consequences and often limit the use of the mapping technology to the operating room. In this work, we report on a scalable technique for the fabrication of large-area soft robotic electrode arrays and their deployment on the cortex through a square-centimeter burr hole using a pressure-driven actuation mechanism called eversion. The deployable system consists of up to six prefolded soft legs, and it is placed subdurally on the cortex using an aqueous pressurized solution and secured to the pedestal on the rim of the small craniotomy. Each leg contains soft, microfabricated electrodes and strain sensors for real-time deployment monitoring. In a proof-of-concept acute surgery, a soft robotic electrode array was successfully deployed on the cortex of a minipig to record sensory cortical activity. This soft robotic neurotechnology opens promising avenues for minimally invasive cortical surgery and applications related to neurological disorders such as motor and sensory deficits.

Clinical application and research progress of extracellular slow wave recording in the gastrointestinal tract

The physiological function of the gastrointestinal (GI) tract is based on the slow wave generated and transmitted by the interstitial cells of Cajal. Extracellular myoelectric recording techniques are often used to record the characteristics and propagation of slow wave and analyze the models of slow wave transmission under physiological and pathological conditions to further explore the mechanism of GI dysfunction. This article reviews the application and research progress of electromyography, bioelectromagnetic technology, and high-resolution mapping in animal and clinical experiments, summarizes the clinical application of GI electrical stimulation therapy, and reviews the electrophysiological research in the biliary system.

Gastroparesis: A Multidisciplinary Approach to Management

Gastroparesis is a neuromuscular disorder whose hallmark is delayed gastric emptying. It is a global challenge to the healthcare system because of poor treatment satisfaction for both the patients and clinicians, eventually leading to a reduction in the quality of life, with antecedent anxiety and depression. Although it is multifactorial in origin, diabetic, idiopathic, and drug-induced gastroparesis are the major risk factors. Disrupted interstitial cells of Cajal (ICC) and gastric dysrhythmia are pivotal to the pathogenesis, with most of the investigations targeted toward assessing gastric emptying and accommodation usually affected by distorted ICC and other neural networks. The treatment challenges can be overcome by a multidisciplinary approach involving gastroenterologists, gastrointestinal surgeons, biomedical engineers, nutritionists, psychologists, nurses, radionuclide radiologists, pharmacists, and family physicians. The exploration of the fundamental physiological processes underlying gastroparesis with the use of biomechanical materials should be given more attention by biomedical engineers to integrate innovative engineering with medicine for solving complex medical issues.

Gastric interoception and gastric myoelectrical activity in bulimia nervosa and binge-eating disorder

OBJECTIVE

Identifying factors that control food intake is crucial to the understanding and treatment of eating disorders characterized by binge eating. In healthy individuals, stomach distension plays an important role in the development of satiation, but gastric sensations might be overridden in binge eating. The present study investigated the perception of gastric signals (i.e., gastric interoception) and gastric motility in patients experiencing binge-eating episodes, that is, bulimia nervosa (BN) and binge-eating disorder (BED).

METHOD

Twenty-nine patients with BN or BED (ED group) and 32 age-, sex-, and BMI-matched healthy controls (HC group) participated in the study. The onset of satiation and stomach fullness were assessed using a novel 2-step water load test (WLT-II). Gastric myoelectrical activity (GMA) was measured by electrogastrography (EGG) before and after ingestion of noncaloric water.

RESULTS

Individuals in the ED group drank significantly more water until reporting satiation during the WLT-II. The percentage of normal gastric myoelectrical power was significantly smaller in the ED group compared to HC, and negatively related to the number of objective binge-eating episodes per week in patients with BN or BED. Power in the bradygastria range was greater in ED than in HC participants.

DISCUSSION

Patients with EDs have a delayed response to satiation compared to HC participants, together with abnormal GMA. Repeated binge-eating episodes may induce disturbances to gastric motor function.

An Extended-Range Inductive Near-Field Telemetry System for High-Resolution Mapping of Gastrointestinal Activity

We present an extended-range near-field wireless data communication designed for high-resolution mapping of gastrointestinal bioelectrical activity. The system is composed of an implantable unit (IU), a wearable unit (WU) and a stationary unit (SU). The WU transfers power to the IU and recharges its battery through an inductive link, wirelessly; and over the same link, reads the 64-channel slow waves data encoded by a differential pulse position coding algorithm, which is modulated through a load shift-keying technique and sent by a back-telemetry circuit at the IU. To guarantee simultaneous WU-IU wireless power transfer and maximize the IU-WU data transfer rate, the duty cycle of the data stream is reduced to 6.25%. A newly designed 13.56 MHz high-power radio frequency power amplifier at the WU, extends the efficient range of IU-WU near-field data communication and power transfer. The retrieved data at the WU are either transmitted to the SU via a 2.4 GHz RF link for real-time monitoring or stored locally on a memory card. The measurements on the implemented system, demonstrate IU-WU data transfer rate of 125 kb/s, while the distance between the transmitter and receiver coils can reach up to 7 cm while maintaining the specific absorption rate below the guidelines.

A High-Resolution Wireless Power Transfer and Data Communication System for Studying Gastric Slow Waves

We present a wireless recording system designed for high-resolution mapping of gastric slow-wave signals. The system is composed of an implantable unit (IU), a wearable unit (WU), and a stationary unit (SU) connected to a computer. Two independent wireless data communication links consisting of IU-WU and IU-SU were developed based on near-field and far-field communication, respectively. Furthermore, the WU is capable to wirelessly recharge the IU's battery through an inductive link. For the IU-WU near-field communication, a differential pulse position data encoding algorithm with only 6.25% duty cycle, with load shift keying (LSK) modulation is developed to guarantee continuous power transmission and high data transfer rate, simultaneously. The IU sends the encoded data to the WU, and the WU can either store the data locally on a memory card or transmit them to the SU for real-time monitoring. In addition, the IU-SU far-field data communication was developed based on a RF transceiver in which the IU transmits the data directly to the SU. The benchtop validation of the system demonstrated successful IU-WU and WU-SU data transmission, while sample signals were recorded successfully at IU through saline solution and received by SU.

An Ultrasonically Powered Wireless System for In Vivo Gastric Slow-Wave Recording

This paper summarizes our recent progress towards Gastric Seed which is an ultrasonically interrogated millimeter-sized implant for gastric electrical activity (also known as slow waves, SWs) recording. We present a proof-of-concept wireless system designed to collect, transmit, and store in vivo SW signals by integrating a prototype Gastric Seed chip, fabricated in a 0.35-μm 2P4M CMOS process, with a commercial-off-the-shelf (COTS) amplifier, 10-bit analog-to-digital converter (ADC), and pair of microcontrollers (MCU) as radio-frequency (RF) transceivers. The chip includes ultrasonic self-regulated power management and addressable pulse-based data transfer. Utilizing two pairs of millimeter-sized stacked power/data ultrasonic transducers spaced by 6 cm in a water tank, the chip achieved a regulated voltage of 2.5 V and a data rate of 16 kbps. The amplifier was configured to have a gain of 60 dB with a 3-dB bandwidth of 18 mHz to 500 mHz. The MCU's built-in 10-bit ADC and RF transceiver were used to digitize the SW signal and transmit the data to a computer. In vivo, SW was recorded wirelessly from the stomach of an anesthetized rat. The recorded SWs showed a frequency of 1.5 cycle-per-minute (cpm) and maximum and minimum amplitudes of 1.03 mV and 0.28 mV peak-to-peak, respectively.

Monitoring and Modulating the Gastrointestinal Activity: A Wirelessly Programmable System with Impedance Measurement Capability

This paper presents the development and benchtop validation of a system that can wirelessly acquire gastric electrical activity called slow-waves (SWs), modulate the gastrointestinal activity through stimulating with low- and high-power current pulses, and measure the tissue bio-impedance over the frequency range of 0.01 - 10 kHz. The developed system is composed of a front-end unit, and a back-end unit connected to a computer. A graphical user interface was designed in LabVIEW to process and display the recorded SWs and measured bio-impedance in real time and to configure the stimulation pulses, wirelessly. Bench-top validation showed an appropriate frequency response for analog conditioning and digitization resolution to acquire SWs. Moreover, the system was able to deliver electrical pulses at amplitudes up to ±10 mA to a maximum load of 1 kΩ. After in vivo studies, the system will be used to diagnose and treat functional gastrointestinal disorders.

Use of Bioelectronics in the Gastrointestinal Tract

Gastrointestinal (GI) motility disorders are major contributing factors to functional GI diseases that account for >40% of patients seen in gastroenterology clinics and affect >20% of the general population. The autonomic and enteric nervous systems and the muscles within the luminal GI tract have key roles in motility. In health, this complex integrated system works seamlessly to transport liquid, solid, and gas through the GI tract. However, major and minor motility disorders occur when these systems fail. Common functional GI motility disorders include dysphagia, gastroesophageal reflux disease, functional dyspepsia, gastroparesis, chronic intestinal pseudo-obstruction, postoperative ileus, irritable bowel syndrome, functional diarrhea, functional constipation, and fecal incontinence. Although still in its infancy, bioelectronic therapy in the GI tract holds great promise through the targeted stimulation of nerves and muscles.

An Implantable Inductive Near-Field Communication System with 64 Channels for Acquisition of Gastrointestinal Bioelectrical Activity

High-resolution (HR) mapping of the gastrointestinal (GI) bioelectrical activity is an emerging method to define the GI dysrhythmias such as gastroparesis and functional dyspepsia. Currently, there is no solution available to conduct HR mapping in long-term studies. We have developed an implantable 64-channel closed-loop near-field communication system for real-time monitoring of gastric electrical activity. The system is composed of an implantable unit (IU), a wearable unit (WU), and a stationary unit (SU) connected to a computer. Simultaneous data telemetry and power transfer between the IU and WU is carried out through a radio-frequency identification (RFID) link operating at 13.56 MHz. Data at the IU are encoded according to a self-clocking differential pulse position algorithm, and load shift keying modulated with only 6.25% duty cycle to be back scattered to the WU over the inductive path. The retrieved data at the WU are then either transmitted to the SU for real-time monitoring through an ISM-band RF transceiver or stored locally on a micro SD memory card. The measurement results demonstrated successful data communication at the rate of 125 kb/s when the distance between the IU and WU is less than 5 cm. The signals recorded in vitro at IU and received by SU were verified by a graphical user interface.