Stretchable Micro-devices towards Digital Transformation

Transparent electrodes (TEs) are crucial in a wide range of modern electronic and optoelectronic devices. However, traditional TEs cannot meet the requirements of smart devices under development in unique fields, such as electronic skins, wearable electronics, robotic skins, flexible and stretchable displays, and solar cells. Emerging TEs printed with nanocrystal (NC) inks are inexpensive and compatible with solution processes, and have huge potential in flexible, stretchable, and wearable devices. Every development in ink-based electrodes makes them more competitive for practical applications in various smart devices. Herein, we provide an overview of emergent ink-based electrodes, such as transparent conducting oxides, metal nanowires, graphene, and carbon nanotubes, and their application in solution-based flexible and stretchable devices.

The development of materials with efficient heat dissipation capability has become essential for next-generation integrated electronics and flexible smart devices. Here, a 3D hybridized carbon film with graphene nanowrinkles and microhinge structures by a simple solution dip-coating technique using graphene oxide (GO) on polyimide (PI) skeletons, followed by high-temperature annealing, is constructed. Such a design provides this graphitized GO/PI (g-GO/PI) film with superflexibility and ultrahigh thermal conductivity in the through-plane (150 ± 7 W m-1 K-1 ) and in-plane (1428 ± 64 W m-1 K-1 ) directions. Its superior thermal management capability compared with aluminum foil is also revealed by proving its benefit as a thermal interface material. More importantly, by coupling the hypermetallic thermal conductivity in two directions, a novel type of carbon film origami heat sink is proposed and demonstrated, outperforming copper foil in terms of heat extraction and heat transfer for high-power devices. The hypermetallic heat dissipation performance of g-GO/PI carbon film not only shows its promising application as an emerging thermal management material, but also provides a facile and feasible route for the design of next-generation heat dissipation components for high-power flexible smart devices.

Manipulation of mechanical properties of monolayer molybdenum disulfide: Kirigami and hetero-structure based approach

With the rapid development of wearable devices, flexible sensors, and flexible displays, higher performance requirements are being placed on conductive materials used in flexible electronic devices. Conductive polymers, known for their excellent flexibility, good conductivity, and tunable molecular structures, have become a research hotspot in the field of flexible electronics. This paper systematically summarizes the design and synthesis strategies of conductive polymers for flexible electronic devices, with a focus on the synthesis methods and structural regulation techniques of typical conductive polymers such as polyaniline (PANI), polypyrrole (PPy), and poly(3,4-ethylenedioxythiophene) (PEDOT). It further analyzes their electrical properties, mechanical performance, and environmental stability in flexible electronics. Finally, the paper discusses future development trends and challenges of conductive polymers in flexible devices, aiming to provide a theoretical foundation and technical support for the research of high-performance flexible electronic materials.

With the rise of artificial intelligence, sensor-based human activity recognition (S-HAR) is increasingly being employed in healthcare monitoring for the elderly, fitness tracking, and patient rehabilitation using smart devices. Inertial sensors have been commonly used for S-HAR, but wearable devices have been demanding more comfort and flexibility in recent years. Consequently, there has been an effort to incorporate stretch sensors into S-HAR with the advancement of flexible electronics technology. This paper presents a deep learning network model, utilizing aggregation residual transformation, that can efficiently extract spatial–temporal features and perform activity classification. The efficacy of the suggested model was assessed using the w-HAR dataset, which included both inertial and stretch sensor data. This dataset was used to train and test five fundamental deep learning models (CNN, LSTM, BiLSTM, GRU, and BiGRU), along with the proposed model. The primary objective of the w-HAR investigations was to determine the feasibility of utilizing stretch sensors for recognizing human actions. Additionally, this study aimed to explore the effectiveness of combining data from both inertial and stretch sensors in S-HAR. The results clearly demonstrate the effectiveness of the proposed approach in enhancing HAR using inertial and stretch sensors. The deep learning model we presented achieved an impressive accuracy of 97.68%. Notably, our method outperformed existing approaches and demonstrated excellent generalization capabilities.

Origami offers two-dimensional (2D) materials with great potential for applications in flexible electronics, sensors, and smart devices. However, the dynamic process, which is crucial to construct origami, is too fast to be characterized by using state-of-the-art experimental techniques. Here, to understand the dynamics and kinetics at the atomic level, we explore the edge effects, structural and energy evolution during the origami process of an elliptical graphene nano-island (GNI) on a highly ordered pyrolytic graphite (HOPG) substrate by employing steered molecular dynamics simulations. The results reveal that a sharper armchair edge is much easier to be lifted up and realize origami than a blunt zigzag edge. The potential energy of the GNI increases at the lifting-up stage, reaches the maximum at the beginning of the bending stage, decreases with the formation of van der Waals overlap, and finally reaches an energy minimum at a half-folded configuration. The unfolding barriers of elliptical GNIs with different lengths of major axis show that the major axis should be larger than 242 Å to achieve a stable single-folded structure at room temperature. These findings pave the way for pursuing other 2D material origami and preparing origami-based nanodevices.

HighlightsLarge-area, lightweight, ultra-flexible, and robust crosslinked MXene-coated PI porous composites were manufactured via a scalable and facile approach.In addition to the hydrophobicity, anti-oxidation and extreme-temperature stability, excellent electromagnetic interference shielding performance was achieved because of the high-efficiency utilization of the building units and microstructure.Moreover, the highly flexible composite foams exhibited excellent electrothermal and electromechanical sensing performance, demonstrating promising perspectives in next-generation flexible electronics, aerospace, and smart devices.

Fabrication of self-recoverable flexible and stretchable electronic devices

Bio-inspired microfluidic systems can be obtained through multidisciplinary approaches by using bio-inspired structural and functional designs for the microfluidic devices. This review mainly focuses on the concept of bio-inspired microfluidics to improve the properties of microfluidic systems for breaking through the bottlenecks of the current microfluidic devices, such as anti-fouling, smart, and dynamic response inside the microchannels under different environments. In addition, here, we show the current research progress of bio-inspired microfluidic systems in applications related to anti-fouling and smart devices, and biomedical research. The review discusses both physical theories and critical technologies in the bio-inspired microfluidics, from biomimetic design to real-world applications, so as to offer new ideas for the design and application of smart microfluidics, and the authors hope this review will inspire the active interest of many scientists in the area of the development and application of soft matter, and multifunctional and smart bio-inspired devices.

The development of flexible and stretchable electronic devices is crucial for advanced electronics, which necessitate inductors with stable performance under deformation. This work presents the fabrication of stretchable polymeric matrices for 3D inductors through a single‐step method via additive manufacturing. A multi‐jet modeling (MJM) type 3D printer is used to print a stretchable and rigid hybrid matrix by leveraging the features of high‐resolution and multi‐component printing techniques. Owing to the presence of access channels designed in multiple directions, the coil channel shows a clean and smooth surface with uniformity. A room‐temperature liquid metal, the eutectic gallium indium (EGaIn) alloy, is encapsulated in the designated channels without any leakage under mechanical deformation. Electrical performance tests demonstrate that the MJM‐printed solenoid and toroid inductors maintain stable performance under bending and stretching deformations, which is suitable for soft electronic applications. Additionally, a flexible helical structured inductor is fabricated and tested as a wireless power receiver inductor. It generated an output voltage of more than 10 V, sufficient to power a red LED light bulb. These results highlight the simplicity and effectiveness of multi‐jet 3D printing for fabricating a stretchable and rigid hybrid matrix for the inductors at once, with excellent mechanical deformability and electrical performance.

Intergenerational support and depressive symptoms: Moderating effects of community services and smart health devices.

Recent advances in smart polymers have taken the fabrication of high-performance flexible and stretchable devices to the next level. The rigid materials for various device components are now being replaced by flexible smart polymers. The fact that the smart polymers respond to the ex situ environment by altering their structures and properties makes them promising materials for making electronic devices. These smart polymers are capable of responding to the changes in physical parameters and can change their physical and chemical properties reversibly. To maintain stability, they can either swell or collapse or covert gel-to-solution and vice versa based on their chemical nature. Different kinds of smart polymers are envisaged, such as pH-sensitive, temperature-sensitive, photo-sensitive and photo-resistive, conductive polymers, hydrogels, anti-inflammatory, shape-memory, self-healing, etc. This chapter gives detailed information on these different types of smart polymers and their fabrication approaches. Furthermore, these polymers have shown great potential in flexible electronic devices for medical diagnosis, biosensors, actuators, lab-on-chip, microfluidic devices, drug delivery, electrochemical sensors, and energy devices like supercapacitors, fuel cells batteries, etc. This chapter also gives an overview of these applications. Further, the chapter discusses the future scope of these polymers.

Interacting with the Web of Things

The development of flexible and stretchable devices is crucial for realizing future electronics. In particular, for dielectric layer, conventional inorganic materials are limited by their brittle nature, while organic materials suffer from a low dielectric constant. Here, a novel intrinsically photopatternable high‐k Parylene‐based thin film (Parylene‐OH) is fabricated via a chemical vapor deposition process based on the Gorham method, which provides pin‐hole free, conformal polymeric film on any type of surface. Parylene‐OH can be photo‐patterned by UV crosslinking without further lithography processes and dielectric constant of Parylene‐OH increases from 6.05 to 7.53 after crosslinking, without degrading other parameters, making it comparable to conventional high‐k dielectric, Al2O3. Flexible In─Ga─Zn─O (IGZO) thin‐film transistors (TFTs) with patterned dielectric layers can withstand higher strain owing to the localized pattern of each unit. A CMOS inverter integrated with n‐type IGZO and p‐type Te TFTs is successfully fabricated. Parylene‐OH can be used in the future of state‐of‐the‐art flexible electronic devices.

There is growing attention and rapid development on flexible electronic devices with electronic materials and sensing technology innovations. In particular, strain sensors with high elasticity and stretchability are needed for several potential applications including human entertainment technology, human–machine interface, personal healthcare, and sports performance monitoring, etc. Significant advancements in wearable and flexible electronic and photonic technologies, are materials science of new and alternative materials and methods of coating and deposition, characterization of flexible and transparent or display electronic devices, the electronics behind new sensor development for wearables and flexible technology, and new device design concepts.The anisotropic properties of a system comprising a guest dye dissolved in an aligned liquid-crystalline host were reported, arising from the combination of the bulk liquid crystal host alignment and the anisotropic shape and absorption characteristics of the dye molecules. For many applications, it is also desirable for a guest–host mixture to exhibit a long useable lifetime in addition to the optical properties described above. Many of the proposed applications involve exposure of the systems to wearable and flexible device, polarisers, smart windows and lasers. The stability of a dye molecule may be strongly dependent on its chemical environment, so the stabilityof a guest–host system may depend on the nature of the host mixture as well as that of the dye. A series of new fluorescent dichroic dyes which included phenylacetylene substituent group to 4-site of the 1,8-dicyanonaphthene were synthesized. All dyes were characterized by nuclear magnetism and high resolution mass spectrum. The dicyanonaphthene fluorescent dichroic dyes meet the application conditions of ‘Guest-host’ display. Phenylacetylene bridge bond is often used for liquid crystal molecular design and synthesis to improve the liquid crystal birefringence because of its excellence stability, optical anisotropy.On the one hand, the addition of the phenylacetylene bond increases the molecular linearity and the aspect ratio, which is more favorable for the arrangement of the dye molecules in the main liquid crystal, thereby increasing the ordered parameters of the dye molecules in the liquid crystal; On the other hand, phenylacetylene bonds can increase the molecular conjugation system and optimize the optical properties of dye molecules. Ester groups as a class of important linking groups have been widely used in the synthesis of diamodal dyes4.The 1,8-naphthalene dinitrile is regarded as the precursor, introduced p-ethynylbenzoic acid at its 4-position and then through the acylation reaction to introduce the alkoxy chain, in order to obtain a greater degree of conjugation, in the main liquid crystal has good solubility and high dichroic dye. Acknowledgements We are grateful to the National Natural Science Foundation of China (21576043), supported by the Fundamental Research Funds for the Central Universities.