Ink‐Based Additive Nanomanufacturing of Functional Materials for Human‐Integrated Smart Wearables

Abstract

Human-integrated devices include wearable and implantable devices for monitoring vital human signals or interacting with the human body. [1-3] The human-integrated devices needed to be tethered to the organs or the human skin for implementing their functions such as sensing and energy harvesting. [4-18] The economical, agile, customizable manufacturing, and integration of multifunctional device modules into networked systems with mechanical compliance and robustness will enable unprecedented human-integrated smart wearables [19-23] and usher in exciting opportunities in emerging technologies such as electronics, [24-29] wearable computation, [30-36] human-machine interface, [37-42] robotics, [43-48] and advanced healthcare. [49-54] The fabrication of stateof-the-art microelectronics involves hightemperature processing steps, which are generally incompatible with the flexible substrates (e.g., paper, polymer, fiber, etc.) [55-61] widely used in the wearable devices. Moreover, the current microfabrication technologies are not well positioned to process the emerging functional nanomaterials (e.g., nanowires [NWs] and 2D materials). [62-65] Such incomparability severely limits the pace of deploying these emerging materials (despite their unprecedented properties) in wearable and flexible device technologies. The additive manufacturing (AM) processes have emerged as potential candidates for addressing the earlier limitations of the current microfabrication technologies in fabricating flexible/wearable printed devices with diversified functionalities, e.g., energy harvesting/storage, sensing, actuation, and computation, leveraging advantages such as maskless processing, versatile ink formulation, low cost, low processing temperature, and scalability. [66-71] Researchers have devoted tremendous efforts to develop the related technologies, and several reviews have provided excellent discussions on the material formulation and process aspects of AM techniques. [63,72-79] However, to our best knowledge, there are few review reports about the ink-based additive nanomanufacturing of functional materials for human-integrated smart wearables. To fill this gap, here we review the recent progress in ink-based

Low cost exoskeleton manipulator using bidirectional triboelectric sensors enhanced multiple degree of freedom sensory system

“…In addition, to further improve the sensing resolution for specific application which requires high precision, various fabrication approaches reported in the relevant researches can be adopted to increase the density of the gratings with the dimension of micrometer level, while maintaining the signal quality. MEMS process, screen printing, etc., have been demonstrated to fabricate the fine-featured gratings for TENGs 35,57,58,60,61 .…”

End-to-end design of wearable sensors

“…In addition, many nanomaterials have outstanding mechanical characteristics in terms of the flexibility and elasticity required for wearable devices. With the increasing interest in flexible electronics, there has been rapid development of advanced fabrication techniques for these materials, such as printing of metal 51 or nanomaterial inks 52 in serpentine patterns 53 or even weaving of metal threads 54 , that allow for their incorporation into deformable wearable substrates. The use of this class is indispensable for wearables in which the general approach is the miniaturization and conversion of traditional electrical devices (namely, circuits, sensors 55 , antennas 56 and integrated power systems 57 ) into a wearable format.…”

Challenges and Opportunities for Printed Electrical Gas Sensors

“…Inks for the fabrication of printed electrical gas sensors typically comprise two or more of the following four components depending on the printing method used: (i) functional materials such as metallic or semiconducting nanomaterials, conductive polymers, 2D nanostructured materials, or carbon-derived materials to act as gas sensitive materials or to construct electrodes/interconnects; ,− (ii) binders such as glass powder, resins, or cellulose acetate to hold together functional particles and provide adhesion to the substrates; − (iii) solvents such as water, ethylene glycol, terpineol, or cyclohexanone to enable printability; and (iv) other additives such as wetting agents for inkjet printing as stabilizers. , The presence, type, and quantities of each component will define the rheological properties of the ink according to the requirements of the printing method. For example, inks intended for inkjet printing require low viscosities (4–30 mPa·s) to enable the formation and ejection of droplets from the nozzle(s) (<100 μm diameter) and high surface tension (20–70 dyn cm –1 ) to avoid dripping during the process.…”