Advanced Soft Materials, Sensor Integrations, and Applications of Wearable Flexible Hybrid Electronics in Healthcare, Energy, and Environment

Abstract

glasses, watches, wristbands, or belts, are either fully or partially composed of planar and rigid materials, which require the use of obtrusive, hard supports or additional bendable strips to be mounted on the human body. Therefore, clinical devices that use the existing wearables cause discomfort and limit monitoring of human physiological data in the laboratory. This is the big limitation factor to overcome despite the ever-growing market for wearables in broader screenings outside of the clinic. By this account, it is necessary to replace the bulky and rigid plastics and metal components in the sensors and electronics with skin-like materials for enhanced wearability and functionality.The concept of WFHE poses a possible solution to address the aforementioned difficulties by providing user comfort, compliant mechanics, soft integration, multifunctionality, and smart diagnostics with embedded machine learning algorithms. Specifically, such electronics would provide stable and intimate contact to the soft human skin without adding any mechanical and thermal loadings or causing skin breakdown. Current development strategies and approaches for advanced WFHE focus on soft, flexible form factors, nonirritating and nontoxic characteristics, fully autonomous energy components, seamless wireless communications, Recent advances in soft materials and system integration technologies have provided a unique opportunity to design various types of wearable flexible hybrid electronics (WFHE) for advanced human healthcare and humanmachine interfaces. The hybrid integration of soft and biocompatible materials with miniaturized wireless wearable systems is undoubtedly an attractiveprospect in the sense that the successful device performance requires high degrees of mechanical flexibility, sensing capability, and user-friendly simplicity. Here, the most up-to-date materials, sensors, and system-packaging technologies to develop advanced WFHE are provided. Details of mechanical, electrical, physicochemical, and biocompatible properties are discussed with integrated sensor applications in healthcare, energy, and environment. In addition, limitations of the current materials are discussed, as well as key challenges and the future direction of WFHE. Collectively, an all-inclusive review of the newly developed WFHE along with a summary of imperative requirements of material properties, sensor capabilities, electronics performance, and skin integrations is provided. Wearable Flexible Hybrid ElectronicsThe ORCID identification number(s) for the author(s) of this article can be found under https://doi.

Recent Developments of Flexible and Stretchable Electrochemical Biosensors

“…Flexible thin-film biosensors can withstand a mechanical strain before fracture (e.g., <1% for paper and <5% for plastic substrates). However, opportunities still exist for electrochemical biosensors when the applied strain from various loading conditions exceeds the fracture limit [177][178][179]. Additionally, the flexible thin-film biosensors cannot conform to the textured surface of the skin at various locations on the human body.…”

Advanced Nanomaterials, Printing Processes, and Applications for Flexible Hybrid Electronics

“…Inkjet printing has the versatility to print various materials. Several 2D nanomaterials have been used, including MXene, which is a highly conductive, mechanically robust, and controllable transition metal carbide [103,104]. Interestingly, the unique material composition determines the bandgap state of Mxene, which means that MXene can be a conductor or semiconductor [105].…”

“…In this application, conformal contact on human skin, high precision, fast response, good repeatability, and long-term stability are required. The wearable temperature sensors should function in the temperature range from 25 to 40 • C, in which all values of human temperature conditions are covered [103]. In addition, high accuracy with a clinically desired resolution of 0.01 • C is also necessary.…”

“…Strain sensors convert external mechanical deformation into an electrical signal of sensing materials [191]. There are many types of sensing principle: piezoresistivity, piezoelectricity, capacitance, percolation network, crack propagation, resonant frequency shift, and triboelectricity [103]. A strain sensor with a higher gauge factor has better sensibility, with which the subtle motions of the subject can be detected.…”

Crack Tip Field of a Double-Network Gel: Visualizing Covalent Bond Scission by Mechanoradical Polymerization

“…Mechanically robust soft materials attract significant interests not only for fundamental science 1−5 but also for the requirements in emerging applications including medical implants, 6,7 soft robots 8,9 and wearable soft electronics. 10,11 For the practical application to ensure the mechanical reliability, toughness, i.e. crack resistance of the materials, is crucially important along with a high strength and an appropriate stiffness.…”