Screen-Printed Corrosion-Resistant and Long-Term Stable Stretchable Electronics Based on AgAu Microflake Conductors

Miniaturized Soft and Stretchable Multilayer Circuits through Laser-Defined High Aspect-Ratio Printing

Stretchable electronics enable seamless integration of wearables with the human body, thereby creating new opportunities in biomedical applications. Miniaturized multilayer stretchable printed circuit boards are key for achieving high functional density circuits with minimal footprint. However, current microfabrication technologies struggle with simultaneously achieving tissue-like softness (<<1 MPa), high resolution and low sheet resistance. This study demonstrates a scalable printing method that enables ultra-soft (<0.4 MPa) stretchable conductors (>300% strain) with high-resolution (<2.5 µm width) and high aspect-ratio tracks (>1) connected by ultra-fine (20 µm) vertical-interconnect-access (VIA) for multi-layered configurations. The method is based on stencil printing into laser-defined bio-masks comprising the abundant biopolymer lignin, thereby achieving printing capabilities beyond conventional methods in a sustainable manner. Based on the unique capabilities, a miniaturized multilayer ultra-soft wireless near-field-communication temperature logger is developed. Laser-defined printing can pave the way for the next generation of ultra-soft miniaturized wearables.

Development of Highly Stretchable Ag-MWCNT Composite for Screen-Printed Textile Electronics with Improved Mechanical and Electrical Properties

Introduction

The rapid growth of flexible and wearable electronics has created a need for materials that offer both mechanical durability and high conductivity. Textile electronics, which integrate electronic pathways into fabrics, are pivotal in this field but face challenges in maintaining stable electrical performance under mechanical strain. This study develops highly stretchable silver multi-walled carbon nanotube (Ag-MWCNT) composites, tailored for screen printing and heat-transfer methods, to address these challenges.

Methods

Silver flakes dispersed in a thermoplastic polyurethane (TPU) matrix formed the base composite, which was initially evaluated under tensile and cyclic stretching conditions. Resistance drift observed in these tests prompted the incorporation of multi-walled carbon nanotubes (MWCNTs). Leveraging their high aspect ratio and conductivity, MWCNTs were homogenized into the composite at varying concentrations. The resulting Ag-MWCNT composites were assessed through cyclic stretching and thermal shock tests to evaluate electrical and mechanical performance.

Results

Incorporating MWCNTs improved composite performance, reducing resistance change amplitude by 40% and stabilizing resistance within 2-8 Ohms under mechanical stress. These materials demonstrated superior electrical stability and durability, maintaining consistent performance over extended use compared to Ag/TPU alone.

Discussion

This study highlights the critical role of MWCNTs in enhancing the reliability of conductive composites for textile electronics. By addressing resistance drift and stabilizing electrical properties, these advancements enable more robust and long-lasting wearable technologies. The demonstrated feasibility of combining screen-printing and heat-transfer techniques provides a scalable approach for manufacturing flexible electronics, paving the way for further innovation in industrial applications.

Kill Two Birds with One Stone: Cracking Lithography Technology for High-Performance Flexible Metallic Network Transparent Conductors and Metallic Micronano Sheets

Flexible electronics have sparked a wide range of exciting applications, such as flexible display technologies, lighting, sensing, etc. Flexible conductors are essential components of flexible electronics and seriously affect efficiency and overall performance. Here, a facile and kill-two-birds-with-one-stone strategy of cracking lithography technology has been proposed to simultaneously fabricate two high-performance flexible conductors, flexible metallic network transparent conductors (f-NTCs) and metallic micronano sheets (MMNSs). The PET substrate flexible transparent conductors (FTCs) based on this strategy yield 88.1% transparency within the visible spectrum and a sheet resistance of 9 Ω/sq. In addition, the FTCs show exceptional mechanical stability, with the sheet resistance remaining virtually unchanged even after 6000 s of bending tests. Subsequently, the remaining MMNSs are recycled to manufacture a Ag paste, showing a very low conductive percolation threshold (∼13%) and excellent flexibility with 140% breaking elongation. After 1000 s of stretching tests, it showed excellent mechanical stability. Furthermore, flexible electroluminescent devices based on the FTCs and sensors fabricated with MMNSs both show excellent performance, demonstrating their potential wide applications in flexible electronics.

Stretchable Tissue-Like Gold Nanowire Composites with Long-Term Stability for Neural Interfaces

Soft and stretchable nanocomposites can match the mechanical properties of neural tissue, thereby minimizing foreign body reactions to provide optimal stimulation and recording specificity. Soft materials for neural interfaces should simultaneously fulfill a wide range of requirements, including low Young's modulus (<<1 MPa), stretchability (≥30%), high conductivity (>> 1000 S cm-1), biocompatibility, and chronic stability (>> 1 year). Current nanocomposites do not fulfill the above requirements, in particular not the combination of softness and high conductivity. Here, this challenge is addressed by developing a scalable and robust synthesis route based on polymeric reducing agents for smooth, high-aspect ratio gold nanowires (AuNWs) of controllable dimensions with excellent biocompatibility. AuNW-silicone composites show outstanding performance with nerve-like softness (250 kPa), high conductivity (16 000 S cm-1), and reversible stretchability. Soft multielectrode cuffs based on the composite achieve selective functional stimulation, recordings of sensory stimuli in rat sciatic nerves, and show an accelerated lifetime stability of >3 years. The scalable synthesis method provides a chemically stable alternative to the widely used AgNWs, thereby enabling new applications within electronics, biomedical devices, and electrochemistry.

Dual-Circularly Polarized and Flexible Metasurface Antenna Based on Graphene Assembled Film for Satellite Communications

Traditional metal materials used in electronic devices are often problematic due to issues like bending resistance, oxidation leading to failure, and environmental pollution. To address these challenges, microwave electronic devices are constantly casting around for metal substitute materials with additional characteristics such as flexibility, anticorrosive, and eco-friendly. However, finding suitable materials that are accessible for radiofrequency (RF) applications is a difficult yet promising task. Consequently, a high-performance metasurface antenna based on highly conductive graphene films for satellite communications is developed in this paper. The proposed graphene assembled films (GAFs) have a conductivity of up to 1.13 × 106 S/m. Simulation and measurement results confirm the excellent performance of the designed antenna. Comparative experiments are also conducted on salt spray and mechanical bending between GAF antenna patterns and copper foil counterparts, further demonstrating the outstanding flexible property and corrosion resistance performance of prepared GAFs.

A Guide to Printed Stretchable Conductors

Printing of stretchable conductors enables the fabrication and rapid prototyping of stretchable electronic devices. For such applications, there are often specific process and material requirements such as print resolution, maximum strain, and electrical/ionic conductivity. This review highlights common printing methods and compatible inks that produce stretchable conductors. The review compares the capabilities, benefits, and limitations of each approach to help guide the selection of a suitable process and ink for an intended application. We also discuss methods to design and fabricate ink composites with the desired material properties (e.g., electrical conductance, viscosity, printability). This guide should help inform ongoing and future efforts to create soft, stretchable electronic devices for wearables, soft robots, e-skins, and sensors.

Future Thread: Printing Electronics on Fibers

This article introduces a methodology to increase the integration density of functional electronic features on fibers/threads/wires through additive deposition of functional materials via printed electronics. It opens the possibility to create a multifunctional intelligent system on a single fiber/thread/wire while combining the advantages of existing approaches, i.e., the scalability of coating techniques and the microfeatures of semiconductor-based fabrication. By directly printing on threads (of diameters ranging from 90 to 1000 μm), micropatterned electronic devices and multifunctional electronic systems could be formed. Contact and noncontact printing methods were utilized to create various shapes from serpentines and meanders to planar coils and interdigitated electrodes, as well as complex multilayer structures for thermal and light actuators, humidity, and temperature sensors. We demonstrate the practicality of the method by integrating a multifunctional thread into a FFP mask for breath monitoring. Printing technologies provide virtually unrestricted choices for the types of threads, materials, and devices used. They are scalable via roll-to-roll processes and offer a resource-efficient way to democratize electronics across textile products.