Hydrogel-Templated Transfer-Printing of Conductive Nanonetworks for Wearable Sensors on Topographic Flexible Substrates.

Transfer-printing enables the assembly of functional nanomaterials on unconventional substrates with a desired layout in a controllable manner. However, transfer-printing to substrates with complex surfaces remains a challenge. Herein, we show that hydrogels serve as effective template material platforms for the assembly and transfer-printing of conductive nanonetwork patterns for flexible sensors on various topographic surfaces in a very simple yet versatile manner. The non-adherence, nanoporous structure, and molding capability of the hydrophilic hydrogel enable the assembly of conductive nanonetwork patterns on the hydrogel surface and transfer of the nanonetworks onto various flexible and topographic substrates. Flexible strain sensors and pressure sensors that monitor finger motions and arterial pulses are successfully demonstrated using the hydrogel-templated approach. The rich chemistry of polymeric networks, facile molding capability, and biocompatibility of hydrogels could be further combined with additive technology for hydrogels and electronic materials for emerging four-dimensional functional materials and soft bioelectronics.

Redox-Triggered Coloration Mechanism of Electrically Tunable Colloidal Photonic Crystals.

Electrically tunable colloidal photonic crystals (ETPCs) have been investigated because of several merits such as easy color tunability, no discoloration, and clear color. The coloration mechanism of ETPCs has been explained in terms of only the electric field. Herein, we report on a new mechanism: electric field plus redox reaction. Specifically, the coloration behavior of ETPCs was investigated under electrically conductive or insulated conditions using current-voltage, cyclic voltammetry, and zeta potential measurements, as well as scanning electron microscopy. Electrophoretic movement of ETPC particles toward the positive electrode was caused by the electric field due to the particles' negative surface charge. At the positive electrode, ETPC particles lost their electrons and formed a colloidal crystal structure. Finally, an ETPC transparent tube device was constructed to demonstrate the coloration mechanism.

Pulsed radiofrequency on radial nerve under ultrasound guidance for treatment of intractable lateral epicondylitis.

Lateral epicondylitis is a painful and functionally limiting disorder. Although lateral elbow pain is generally self-limiting, in a minority of people symptoms persist for a long time. When various conservative treatments fail, surgical approach is recommended. Surgical denervation of several nerves that innervate the lateral humeral epicondyle could be considered in patients with refractory pain because it denervates the region of pain. Pulsed radiofrequency is a minimally invasive procedure that improves chronic pain when applied to various neural tissues without causing any significant destruction and painful complication. This procedure is safe, minimally invasive, and has less risk of complications relatively compared to the surgical approach. The radial nerve can be identified as a target for pulsed radiofrequency lesioning in lateral epicondylitis. This innovative method of pulsed radiofrequency applied to the radial nerve has not been reported before. We reported on two patients with intractable lateral epicondylitis suffering from elbow pain who did not respond to nonoperative treatments, but in whom the ultrasound-guided pulsed radiofrequency neuromodulation of the radial nerve induced symptom improvement. After a successful diagnostic nerve block, radiofrequency probe adjustment around the radial nerve was performed on the lateral aspect of the distal upper arm under ultrasound guidance and multiple pulsed treatments were applied. A significant reduction in pain was reported over the follow-up period of 12 weeks.

Enhancement of Osteoblast Differentiation Using No-Ozone Cold Plasma on Human Periodontal Ligament Cells.

Periodontitis is an inflammatory disease that leads to periodontal tissue destruction and bone resorption. Proliferation and differentiation of cells capable of differentiating into osteoblasts is important for reconstructing periodontal tissues destroyed by periodontitis. In this study, the effects of the nozone (no-ozone) cold plasma (NCP) treatment on osteoblastic differentiation in periodontal ligament (PDL) cells were investigated. To test the toxicity of NCP on PDL cells, various NCP treatment methods and durations were tested, and time-dependent cell proliferation was analyzed using a water-soluble tetrazolium salts-1 assay. To determine the effect of NCP on PDL cell differentiation, the cells were provided with osteogenic media immediately after an NCP treatment to induce differentiation; the cells were then analyzed using alkaline phosphatase (ALP) staining, an ALP activity assay, real time PCR, and Alizarin Red S staining. The NCP treatment without toxicity on PDL cells was the condition of 1-min NCP treatment immediately followed by the replacement with fresh media. NCP increased ALP, osteocalcin, osteonectin, and osteopontin expression, as well as mineralization nodule formation. NCP treatment promotes osteoblastic differentiation of PDL cells; therefore, it may be beneficial for treating periodontitis.

Spirally Wrapped Carbon Nanotube Microelectrodes for Fiber Optoelectronic Devices beyond Geometrical Limitations toward Smart Wearable E-Textile Applications.

Fiber optoelectronics technology has recently attracted attention as enabling various form factors of wearable electronics, and the issue of how to control and optimize the configuration and physical properties of the electrode micropatterns in the microfiber devices has become important. Here, spirally wrapped carbon nanotube (CNT) microelectrodes with a controlled dimension are demonstrated for high-performance fiber optoelectronic devices. Inkjet-printed CNT microelectrodes with the desired dimension on an agarose hydrogel template are rolling-transferred onto a microfiber surface with an efficient electrical interface. A fiber organic field-effect transistor with spirally wrapped CNT microelectrodes verifies the feasibility of this strategy, where the transferred microelectrodes intimately contact the organic semiconductor active layer and the output current characteristics are simply controlled, resulting in characteristics that exceed the previous structural limitations. Furthermore, a fiber organic photodiode with spirally wrapped CNT microelectrodes, when used as a transparent electrode, exhibits a high Ilight/Idark ratio and good durability of bending. This fiber photodiode can be successfully incorporated into a textile photoplethysmography bandage for the real-time monitoring of human vital signals. This work offers a promising and efficient strategy to overcome the geometric factors limiting the performance of fiber-optic optoelectronic devices.

All-Inkjet-Printed Flexible Nanobio-Devices with Efficient Electrochemical Coupling Using Amphiphilic Biomaterials.

Nanostructured flexible electrodes with biological compatibility and intimate electrochemical coupling provide attractive solutions for various emerging bioelectronics and biosensor applications. Here, we develop all-inkjet-printed flexible nanobio-devices with excellent electrochemical coupling by employing amphiphilic biomaterial, an M13 phage, numerical simulation of single-drop formulation, and rational formulations of nanobio-ink. Inkjet-printed nanonetwork-structured electrodes of single-walled carbon nanotubes and M13 phage show efficient electrochemical coupling and hydrostability. Additive printing of the nanobio-inks also allows for systematic control of the physical and chemical properties of patterned electrodes and devices. All-inkjet-printed electrochemical field-effect transistors successfully exhibit pH-sensitive electrical current modulation. Moreover, all-inkjet-printed electrochemical biosensors fabricated via sequential inkjet-printing of the nanobio-ink, electrolytes, and enzyme solutions enable direct electrical coupling within the printed electrodes and detect glucose concentrations at as low as 20 µM. Glucose levels in sweat are successfully measured, and the change in sweat glucose levels is shown to be highly correlated with blood glucose levels. Synergistic combination of additive fabrication by inkjet-printing with directed assembly of nanostructured electrodes by functional biomaterials could provide an efficient means of developing bioelectronic devices for personalized medicine, digital healthcare, and emerging biomimetic devices.

Wearable Piezoresistive Sensors with Ultrawide Pressure Range and Circuit Compatibility Based on Conductive-Island-Bridging Nanonetworks.

Wearable pressure sensors with wide operating pressure ranges and enhanced wearability via seamless integration with circuits can greatly improve the fields of digital healthcare, prosthetic limbs, and human-machine interfaces. Herein, we report an approach based on a conductive-island-bridging nanonetwork to realize wearable resistive pressure sensors that are operative over ultrawide pressure ranges >400 kPa and are circuit-compatible. The sensor has a simple two-layered structure, where nanonetworks of single-walled carbon nanotubes selectively patterned on a surface-modified elastomeric film interface and bridge conductive Au island patterns on printed circuit boards (PCBs). We show that varying the design of the Au islands and the conductivity of the nanonetworks systematically tunes the sensitivity, linearity, and the operation range of the pressure sensor. In addition, introducing microstructured lead contacts into the sensor based on a Au-island-bridging nanonetwork produces a record-high sensitivity of 0.06 kPa-1 at 400 kPa. Furthermore, the PCB that serves as the bottom layer of the pressure sensor and contains embedded interconnects enables facile integration of the sensor with measurement circuits and wireless communication modules. The developed sensor enables the monitoring of wrist pulse waves. Moreover, an insole-shaped PCB-based pressure-sensing system wirelessly monitors pressure distributions and gait kinetics during walking. Our scheme can be extended to other nanomaterials and flexible PCBs and thus provides a simple yet powerful platform for emerging wearable applications.

Hydrodynamic Layer-by-Layer Assembly of Transferable Enzymatic Conductive Nanonetworks for Enzyme-Sticker-Based Contact Printing of Electrochemical Biosensors.

Realizing high-performance electrochemical biosensors in a simple contact-printing-based approach significantly increases the applicability of integrated flexible biosensors. Herein, an enzyme-sticker-based approach that enables flexible and multielectrochemical sensors via simple contact-transfer printing is reported. The enzyme sticker consists of an enzymatic conductive network film and a polymeric support. The enzyme-incorporated nanostructured conductive network showing an efficient electrical coupling was assembled via the hydrodynamic layer-by-layer assembly of redox enzymes, polyelectrolytes, single-walled carbon nanotubes, and a biological glue material, M13 phage. The enzymatic conductive network on a polymeric membrane support was facilely wet contact-transfer printed onto integrated electrode systems by exploiting varying degrees of hydrophilicity displayed by the enzymatic electronic film, polymeric support, and receiving electrodes of the sensor system. The glucose sensors fabricated using the enzyme sticker detected glucose at a concentration of as low as 35 µM and showed high selectivity and stability. Furthermore, a flexible dual-sensor array capable of detecting both glucose and lactate was demonstrated using the versatile enzyme sticker concept. This work presents a new route toward assembling and integrating hybrid nanomaterials with efficient electrochemical coupling for high-performance biosensors and health-monitoring devices as well as for emerging bioelectronics and electrochemical devices.

Highly stretchable resistive pressure sensors using a conductive elastomeric composite on a micropyramid array.

A stretchable resistive pressure sensor is achieved by coating a compressible substrate with a highly stretchable electrode. The substrate contains an array of microscale pyramidal features, and the electrode comprises a polymer composite. When the pressure-induced geometrical change experienced by the electrode is maximized at 40% elongation, a sensitivity of 10.3 kPa(-1) is achieved.