Stretchable, Soft, Wearable Instrumentation for Cardiovascular Disease Monitoring and Alarm

Abstract

Cardiovascular disease (CVD) stands as a leading cause of mortality affecting large populations worldwide, resulting in numerous fatalities annually. Despite significant advancements in medical science leading to the development of various treatment methods, there remains a preference for continuous monitoring of heart health to enable early detection and intervention in CVD, thereby reducing the likelihood of complications and mortality rates. Among the array of diagnostic methods for CVD, electrocardiography (ECG) has a rich history of application and is widely utilized in clinical settings due to its non-invasive nature, making it a gold standard for diagnosing heart abnormalities. ECG is proficient in diagnosing various physiological parameters, encompassing but not limited to the geometry of cardiac chambers, heart rate and rhythm, severity and location of cardiomyocyte, and heart performance under different pharmaceutical or pacing interventions. This multifaceted information plays a crucial role in the detection and diagnosis of conditions such as atrial and ventricular fibrillation, myocardial infarction, myocardial ischemia, coronary artery disease, and cardiac arrhythmias. However, contemporary multi-lead ECG devices used for CVD diagnosis are characterized by large, bulky designs and rigid hardware, limiting their applicability in daily life. To address this limitation, we have developed soft and stretchable electronic devices for three-lead ECG detection. Leveraging optimized mechanical design, flexible materials, and innovative fabrication methods, these devices are stretchable and can be comfortably attached to a patient's chest for long-term ECG signal monitoring.

In this thesis, our focus lies in the development of a stretchable electronics system for three-lead ECG detection. Our objective requirement of the entire system is the high flexibility and stretchability to accommodate the deformability of human skin, ensuring stable attachment. Additionally, the stretchable system must possess the capability to capture and analog bioelectrical signals, integrate wireless data transmission functionality to obviate the need for bulky devices with substantial computational power, and offer the ability to output digital control signals at varying duty cycles and frequencies for activating the feedback alarm system. To achieve these goals, we propose a stretchable electronic platform that integrates conventional rigid integrated chips (IC) with innovative stretchable circuits. The stretchable silicon-based substrate material, along with the copper layer employing a serpentine design, ensures the electronic system's capability to twist, bend, or stretch in various dimensions. A microcontroller integrated into the system has the capacity to acquire seven channels of analog signals at the same time, enabling the capture of human body motion, while simultaneously operating five vibratory haptic feedback actuators by outputting pulse-width modulation signals with varying duty cycles and frequencies. The actuator has been optimized in both mechanical structure and resonant frequency to maximize the haptic feedback. Additionally, the system utilizes a micro Bluetooth Low Energy Module for wireless communication with computers or computational centres, facilitating continuous data exchange of motion data and feedback commands. Furthermore, the system features a coil resonant at 13.56 MHz and a full bridge rectifier for wireless powering and charging. The system enables users to operate humanoid robots while receiving pressure signals from the robot to generate haptic feedback. This study not only serves as the foundation for the stretchable three-lead ECG system through examination and development of a general stretchable electronic platform, it also enables wireless, long-range nursing of CVD patients—an especially crucial function during pandemic periods.

The three-lead ECG system is building upon the initial stretchable electronic system. The circuit adopts a double-layer design to accommodate the increased complexity of the multi-lead ECG system, while maintaining a compact device size. Two layers are interconnected through vertical vias and conductive silver paste. The analog signal capture system undergoes improvements with the integration of amplifiers and filters to enhance the signal-to-noise ratio for ECG signal recording. Bluetooth technology is also employed for continuous and consistent wireless transmission of ECG signals to computational centres, offering a long communication range to minimize interference during daily usage. Additionally, a newly developed Organahydrogel patch with enhanced adhesive strength of 9.9 kPa and remarkable conductivity of 6.5 kΩ facilitates more stable ECG recordings with improved signal quality. Furthermore, the system integrates machine learning algorithms capable of automatically detecting and diagnosing 11 types of abnormal ECG patterns. Vibratory flexible actuators are utilized to generate haptic feedback to users as a warning when abnormalities are detected.

In conclusion, by adoption of new design and fabrication technique, we have overcome the challenges on physical dimension and the interconnection between different components, successfully developed a three-lead ECG system characterized by high stretchability, stability, and comfort. Through detailed research, we addressed several limitations related to robustness, thickness, cable connection, and motion artifacts arising from strenuous exercise. We believe that in the future, the stretchable multi-lead ECG system will find widespread application in clinical settings and the daily lives of high-risk populations, significantly contributing to the prevention of serious cardiovascular diseases.

Date of Award	27 Aug 2024
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Xinge YU (Supervisor)