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Introduction

This chapter first introduces the development of integrated smart micro-systems, aiming at health monitoring-related applications. After the introduction of the working mechanism and structural design of different energy-harvesting units, energy-storage units, and functional units, the related researches focusing on the integration and applications are further carried out. To solve the issues, including complex processing technology, poor device performance, redundant integrated design, and simple applications, integrated smart micro-systems toward health monitoring are proposed. Consequently, the motivation, purpose, and innovative contributions are briefly summarized.

1.1 Overview of Integrated Smart Micro-systems

Since the beginning of the twenty-first century, with the technological innovation of industrial production and the rapid development of Internet applications, tremendous changes have occurred in people's lifestyles. Smart lifestyle has penetrated into all aspects, such as clothing, food, housing, and transportation. It is possible to know the world well without leaving the house. The development of medical and health field is particularly noticeable.

Advances in flexible electronics, the Internet, and processing technology have provided better assistive technical means for seeking medical treatment and physical examination. The health-monitoring approach is transiting from the traditional medical model with the help of large equipment in hospital to wearable micro-systems with real-time monitoring and remote diagnosis, as shown in Figure 1.1.

Under the traditional medical model, "looking, listening, asking, and feeling the pulse" are necessary means. Doctors communicate with patients face-to-face and perform various examinations with the assistance of sophisticated medical equipment. For individuals, this is a hospital-centered diagnosis method, which takes longer time with low efficiency and cannot fully meet the needs of continuous monitoring of certain diseases. The rapid development of various types of wearable devices and flexible micro-systems allows for the opportunities to the fields of medical care and health monitoring.

Figure 1.1 Health-monitoring approaches in the field of medical electronics.

Source: Choi et al. [1]; Lee et al. [2].

1.1.1 The Progress of Portable Smart Micro-systems

The human body produces a variety of physiological signals in the daily metabolism process [3], including physical signals such as body temperature, blood pressure, biopotential, exercise information, respiratory rate, and heart rate, and chemical signals, such as pH, sodium ions, lactate, uric acid, and glucose in body fluids. These physiological signals are very critical for human health management. For example, it is feasible to monitor obstructive sleep apnea hypopnea syndrome (OSAHS) through changes in heart rate [4], and monitor the cystic fibrosis through changes of chloride ion concentration in sweat [5].

With the help of the miniaturization and intelligence of integrated circuits under Moore's law and the timely sharing of data with the development of the Internet, wearable technology has developed rapidly. A series of smart wearable devices for health monitoring are proposed, such as the new generation of Apple Watch. Authorized by the US Federal Drug Administration (FDA), it can achieve the same accuracy as the clinical electrocardiogram monitor to provide diagnosis and early warning for patients to understand their physical conditions in time.

The entire market of wearable devices is developing rapidly. In 2016, the total number of wearable devices in the global market reached 125 million units. It is estimated that by 2021, the overall number will be close to 900 million units, with an average compound annual growth rate of 23% [6]. According to IDTechEx data, the market share of the wearable health field will grow to more than US$75 billion by 2025 [7], and it will gradually develop into a patient-centered medical health model.

Figure 1.2 Development progress of portable health-monitoring methods.

Source: Yu Song.

Figure 1.2 lists the current monitoring methods of various physiological signals. Most of these detection modules use portable and miniaturized equipment, which adopt the working modes of pre-sampling and in vitro off-line detection. It is hard to obtain real-time physiological information and perform long-term continuous monitoring. In addition, most of these commonly used wearable devices are based on silicon-based rigid materials with hard modules, which lacks in biocompatibility. Due to the mismatch of Young's modulus between the device and human skin, it is unavailable to realize skin-interfaced measurement of physiological signals directly. Meanwhile, during the normal movements, these rigid modules will be inevitably misaligned with the soft skin, resulting in the poor accuracy of detection and reduced reliability in health diagnosis. These issues greatly limit the practical applications of wearable devices in real-time monitoring of human health.

With the rapid development of material science, chemical analysis technology, and flexible fabrication process, the flexible and integrated smart micro-systems toward health monitoring have attracted huge attention [8-10]. The advantages of lightweight, soft, cheap, and durable properties enable the continuous, sensitive, and accurate monitoring of various physiological information when comfortably attached to the human skin. The further cooperation with wireless signal transmission allows for in situ detection and on-demand therapy with the assistance of big data analysis. It is feasible to achieve the ultimate goal of personalized medical care and dynamic health management based on the integrated smart micro-systems [11-13].

1.1.2 Integrated Smart Micro-systems Toward Healthcare Monitoring

The exploration of flexible bioelectronics technology and the in-depth research of flexible polymer and multifunctional nanomaterials facilitate the rapid development of integrated smart micro-systems for health monitoring, and break through the limitations of large medical equipment with poor portability and wearable devices with low sensitivity. Through the materials selection, fabrication optimization, structural design, and seamless integration, the smart micro-systems can be directly attached to the human skin to achieve accurate monitoring of various physiological signals. The schematic of specific health monitoring and remote diagnosis is shown in Figure 1.3.

On the one hand, various energy-harvesting and -storage devices can efficiently convert human mechanical energy into electrical energy [14-16] and effectively store the energy as a stable power supply [17-19]. On the other hand, through structural design and material optimization, miniaturized multimodal biosensors can continuously acquire physiological signals and provide reliable health information [20-22].

During the measurement of physiological signals, the single transmission and analysis are of vital importance. The sensor data are sent to user interface by the circuit module with Bluetooth low-energy or Wi-Fi wireless chip. Through the design of relevant applications, it is available to perform real-time signal analysis and rapid response. Doctors can acquire the key health-related parameters remotely to monitor the patients' conditions, such as respiration rate, electrocardiogram (ECG) signal, and temperature. It is feasible to answer the questions online for minor illness, conduct early warning interventions for critically ill patients, and arrange in-patient medical care in time.

The integrated smart micro-systems toward health monitoring consist of three core units: an energy-harvesting unit that converts various types of energy into electrical energy, an energy-storage unit that effectively stores electrical energy, and the functional units that transform external stimuli into electrical signals. The core units and representative devices of the integrated smart micro-systems are shown in Figure 1.4.

The coordination and integration of three units enable closed-loop smart micro-systems, which continuously acquire various physiological signals from human body, perform health status alarm with wireless data transmission and signal processing, and provide diagnosis and personalized health management with improved efficiency. The current advances and challenges of these units and applications will be discussed in detail in the following sections.

Figure 1.3 Schematic illustration of integrated smart micro-systems toward health monitoring.

Source: Yu Song.

Figure 1.4 Core units and representative devices of smart micro-systems toward health monitoring.

Source: Bandodkar et al. [14]. Copyright 2017, Royal Society of Chemistry. Lee et al. [15]. Copyright 2014, John Wiley & Sons. Ouyang et al....