Recent advances in nanomaterials and nano-microfabrication have enabled the development of flexible wearable electronics. However, existing manufacturing methods still rely on a multi-step, error-prone complex process that requires a costly cleanroom facility. Here, we report a new class of additive nanomanufacturing of functional materials that enables a wireless, multilayered, seamlessly interconnected, and flexible hybrid electronic system. All-printed electronics, incorporating machine learning, offers multi-class and versatile human-machine interfaces. One of the key technological advancements is the use of a functionalized conductive graphene with enhanced biocompatibility, anti-oxidation, and solderability, which allows a wireless flexible circuit. The high-aspect ratio graphene offers gel-free, high-fidelity recording of muscle activities. The performance of the printed electronics is demonstrated by using real-time control of external systems via electromyograms. Anatomical study with deep learning-embedded electrophysiology mapping allows for an optimal selection of three channels to capture all finger motions with an accuracy of about 99% for seven classes.

Monodispersed Pt nanocatalyst-doped and undoped assemblies of single-walled carbon nanotubes (SWCNTs) were aligned with high anisotropy on a multi-layered ceramic/metal electrode system (MLES), which was used as a cheap and cost-effective electrode system, by dielectrophoretic orientation to form linear dense assemblies of SWCNTs (LACNTs). It is envisaged that they can be used as a potentially inexpensive platform for multi-gas sensing nano-devices. To form homogeneously dispersed Pt nanocatalysts (NCs), an aqueous chloroplatinic acid solution (H₂PtCl₆) was deposited on the surface of acid-treated SWCNTs. This was followed by alignment under the application of alternative currents ranging from 5 kHz to 50 MHz to create electrically conducting LACNT bundles on the MLES platform and reduction under hydrogen plasma. The analysis showed that the Pt nanocatalysts (2 nm_av, deviation: ±1 nm) are monodispersed on the SWCNTs, which contributed to a noticeable enhancement in the gas sensing properties towards H₂, NO₂, H₂S and NH₃ gases. In addition, the principal component analysis results showed fairly good discrimination of the gases by employing a sensor array composed of Pt/LACNTs and SWCNTs, and the hydrogen sensing performance was high in terms of sensitivity compared to other literature studies. This gas sensing device based on an MLES may pave the way for extended applications of new multi-gas sensing devices as a low-cost and life-long gas sensing platform.

Ink-jet printed conductive copper patterns with enhanced substrate adhesion were fabricated using a conductive copper ink containing a silane coupling agent as an adhesion promoter. The effect of the silane coupling agent on the copper complex ion ink properties, including viscosity and surface tension, was systematically investigated. The copper complex ion ink that was ink-jet printed on a polyimide film was transformed to copper films by thermal treatment at 200 °C for 2 h in H₂. The phase, microstructure, resistivity and peel strength were examined by X-ray diffraction, field emission scanning electron microscopy, the four-point probe technique, the 90° peel test and the ASTM D3359 tape test. The proper amount of silane coupling agent was determined according to the electrical conductivities and adhesive strengths of the ink-jet printed copper patterns containing varied amounts of adhesion promoter. As a result, the patterns formed from copper complex ion ink containing 3 wt% silane coupling agent exhibited not only the highest peel strength (240.3 gf mm⁻¹ and 4B) but also low resistivity (approx. 20 μΩ cm). The mechanism of adhesion promotion via the silane coupling agent was also suggested.

Inkjet-printed electronics using metal particles typically lack electrical conductivity and interfacial adhesion with an underlying substrate. To address the inherent issues of printed materials, this paper introduces advanced materials and processing methodologies. Enhanced adhesion of the inkjet-printed copper (Cu) on a flexible polyimide film is achieved by using a new surface modification technique, a nanostructured self-assembled monolayer (SAM) of (3-mercaptopropyl)trimethoxysilane. A standardized adhesion test reveals the superior adhesion strength (1192.27 N/m) of printed Cu on the polymer film, while maintaining extreme mechanical flexibility proven by 100,000 bending cycles. In addition to the increased adhesion, the nanostructured SAM treatment on printed Cu prevents formation of native oxide layers. Combined with newly synthesized Cu ink and associated sintering technique with an intense pulsed ultraviolet and visible light absorption, it enables ultrahigh conductivity of printed Cu (2.3 x 10^-6 Ω∙cm), which is the highest electrical conductivity reported to date. The comprehensive materials engineering technologies offer highly reliable printing of Cu patterns for immediate use in wearable flexible hybrid electronics. In vivo demonstration of printed, skin-conformal Cu electrodes indicates a very low skin-electrode impedance (< 50 kΩ) without a conductive gel and successfully measures three types of biopotentials, including electrocardiograms, electromyograms, and electrooculograms.