Preparation of MWCNT/PDMS Conductive Micro-Patterned Nanocomposites

Nanomaterial-Based Electrically Conductive Hydrogels for Cardiac Tissue Repair

Cardiovascular disease is one of major causes of deaths, and its incidence has gradually increased worldwide. For cardiovascular diseases, several therapeutic approaches, such as drugs, cell-based therapy, and heart transplantation, are currently employed; however, their therapeutic efficacy and/or practical availability are still limited. Recently, biomaterial-based tissue engineering approaches have been recognized as promising for regenerating cardiac function in patients with cardiovascular diseases, including myocardial infarction (MI). In particular, materials mimicking the characteristics of native cardiac tissues can potentially prevent pathological progression and promote cardiac repair of the heart tissues post-MI. The mechanical (softness) and electrical (conductivity) properties of biomaterials as non-biochemical cues can improve the cardiac functions of infarcted hearts by mitigating myocardial cell death and subsequent fibrosis, which often leads to cardiac tissue stiffening and high electrical resistance. Consequently, electrically conductive hydrogels that can provide mechanical strength and augment the electrical activity of the infarcted heart tissue are considered new functional materials capable of mitigating the pathological progression to heart failure and stimulating cardiac regeneration. In this review, we highlight nanomaterial-incorporated hydrogels that can induce cardiac repair after MI. Nanomaterials, including carbon-based nanomaterials and recently discovered two-dimensional nanomaterials, offer great opportunities for developing functional conductive hydrogels owing to their excellent electrical conductivity, large surface area, and ease of modification. We describe recent results using nanomaterial-incorporated conductive hydrogels as cardiac patches and injectable hydrogels for cardiac repair. While further evaluations are required to confirm the therapeutic efficacy and toxicity of these materials, they could potentially be used for the regeneration of other electrically active tissues, such as nerves and muscles.

High-Quality Microprintable and Stretchable Conductors for High-Performance 5G Wireless Communication

With the advent of 5G wireless and Internet of Things technologies, flexible and stretchable printed circuit boards (PCBs) should be designed to address all the specifications necessary to receive signal transmissions, maintaining the signal integrity, and providing electrical connections. Here, we propose a silver nanoparticle (AgNP)/silver nanowire (AgNW) hybrid conductor and high-quality microprinting technology for fabricating flexible and stretchable PCBs in high-performance 5G wireless communication. A simple and low-cost reverse offset printing technique using a commercial adhesive hand-roller was adapted to ensure high-resolution and excellent pattern quality. The AgNP/AgNW micropatterns were fabricated in various line widths, from 5 μm to 5 mm. They exhibited excellent pattern qualities, such as fine line spacing, clear edge definition and outstanding pattern uniformity. After annealing via intense pulsed light irradiation, they showed outstanding electrical resistivity (15.7 μΩ cm). Moreover, they could withstand stretching up to a strain of 90% with a small change in resistance. As a demonstration of their practical application, the AgNP/AgNW micropatterns were used to fabricate 5G communication antennas that exhibited excellent wireless signal processing at operating frequencies in the C-band (4-8 GHz). Finally, a wearable sensor fabricated with these AgNP/AgNW micropatterns could successfully detected fine finger movements in real time with excellent sensitivity.

Strain Sensing Behavior of 3D Printable and Wearable Conductive Polymer Composites Filled with Silane-Modified MWCNTs

3D printing of conductive polymers is an attractive technique for achieving high flexibility, wearability, and sensing characteristics without geometrical limitations. However, there is an urgent need to integrate printability, conductivity, and sensing capability. Herein, a conductive polymer ink for 3D printing that combines the desirable features of high electrical conductivity, flexible stretchability, and strain-sensing monitoring is prepared. The ink matrix is polydimethylsiloxane and synergistically enhanced by acetylene carbon black (ACB) and multi-walled carbon nanotubes (MWCNTs) (silane or un-silane-modified). The inks are screened step-by-step to explore their printability, rheology, mechanical properties, and electrical performance upon loading. The formation of an electrically conductive network, electrical properties upon tensile load, and strain sensing stability under cyclic stretching are investigated intensively. It is demonstrated that conductive polymers filled by ACB and silane-modified, MWCNTs (MWCNTs-MTES) possess superior printability, stretchability, conductivity, and strain sensing behaviors. Finally, a flexible wearable strain-sensing skin patch is printed, and it successfully records joint motion signals on human fingers, wrists, and elbows with good stability and repeatability. Those results show the extent of potential applications in healthcare and motion monitoring fields. This work provides an efficient and simple route to achieve comfortably wearable and high-performance strain sensors.

Production of elastomer-based highly conductive hybrid nanocomposites and treatment with sulfuric acid

As an elastomer, poly(dimethylsiloxane) (PDMS) is used in various applications such as wearable technology and sealants, and is especially preferred in microelectromechanical device production due to its advantage in fabrication of microstructures. However, some of its applications such as sensor-based or electrode-based are limited due to its insulator aspect. Various conductive nanomaterials such as carbon nanotubes (CNTs), graphene, graphite, carbon black, and silver nanoparticles were incorporated into the PDMS matrix for the production of conductive nanocomposites. In this study, we produced highly conductive PDMS nanocomposites by addition of multiwalled carbon nanotubes (MWCNTs) and graphene nanoplatelets (GNPs) in a three-dimensional network. Due to the synergistic effect between CNTs and GNPs inside a polymeric matrix, we expected to obtain PDMS nanocomposites more conductive than nanocomposites with only CNTs. Additionally, we investigated the effect of sulfuric acid treatment on the electrical conductivity and surface composition of prepared PDMS/MWCNT/GNP nanocomposites. Results indicated that the electrical conductivity in sulfuric acid-treated samples was significantly higher than in untreated samples. Levels of conductivity in the range of 270.7–1074.8 S/m were achieved; the higher ones were the samples treated with sulfuric acid solution.