Fully Additively Manufactured Counter Electrodes for Dye-Sensitized Solar Cells.

In dye-sensitized solar cells (DSSCs), the counter electrode (CE) plays a crucial role as an electron transfer agent and regenerator of the redox couple. Unlike conventional CEs that are generally made of glass-based substrates (e.g., FTO/glass), polymer substrates appear to be emerging candidates, owing to their intrinsic properties of lightweight, high durability, and low cost. Despite great promise, current manufacturing methods of CEs on polymeric substrates suffer from serious limitations, including low conductivity, scalability, process complexity, and the need for dedicated vacuum equipment. In the present study, we employ and evaluate a fully additive manufacturing route that can enable the fabrication of CEs for DSSCs in a high-throughput and eco-friendly manner with improved performance. The proposed approach sequentially comprises: (1) material extrusion 3-D printing of polymer substrate; (2) conductive surface metallization through cold spray particle deposition; and (3) over-coating of a thin-layer catalyzer with a graphite pencil. The fabricated electrodes are characterized in terms of microstructure, electrical conductivity, and photo-conversion efficiency. Owing to its promising electrical conductivity (8.5 × 104 S·m-1) and micro-rough surface structure (Ra ≈ 6.32 µm), the DSSCs with the additively manufactured CEs led to ≈2.5-times-higher photo-conversion efficiency than that of traditional CEs made of FTO/glass. The results of the study suggest that the proposed additive manufacturing approach can advance the field of DSSCs by addressing the limitations of conventional CE manufacturing platforms.

In Situ Spray Polymerization of Conductive Polymers for Personalized E-textiles.

E-textiles, also known as electronic textiles, seamlessly merge wearable technology with fabrics, offering comfort and unobtrusiveness and establishing a crucial role in health monitoring systems. In this field, the integration of custom sensor designs with conductive polymers into various fabric types, especially in large areas, has presented significant challenges. Here, we present an innovative additive patterning method that utilizes a dual-regime spray system, eliminating the need for masks and allowing for the programmable inscription of sensor arrays onto consumer textiles. Unlike traditional spray techniques, this approach enables in situ, on-the-fly polymerization of conductive polymers, enabling intricate designs with submillimeter resolution across fabric areas spanning several meters. Moreover, it addresses the nozzle clogging issues commonly encountered in such applications. The resulting e-textiles preserve essential fabric characteristics such as breathability, wearability, and washability while delivering exceptional sensing performance. A comprehensive investigation, combining experimental, computational, and theoretical approaches, was conducted to examine the critical factors influencing the operation of the dual-regime spraying system and its role in e-textile fabrication. These findings provide a flexible solution for producing e-textiles on consumer fabric items and hold significant implications for a diverse range of wearable sensing applications.

Enhanced Performance of Triboelectric Nanogenerators and Sensors via Cold Spray Particle Deposition.

In this study, a high-performance triboelectric nanogenerator (TENG) is developed based on cold spray (CS) deposition of composite material layers. Composite layers were fabricated by cold spraying of micron-scale tin (Sn) particles on aluminum (Al) and polytetrafluoroethylene (PTFE) films, which led to improved TENG performance owing to functionalized composite layers as friction layers and electrodes, respectively. As-sprayed tin composite layers not only enhanced the flow of charges by strong adhesion to the target layer but also formed a nano-microstructure on the surface of the layers, thereby increasing the surface area during friction. More importantly, the electricity generation performance was improved more than 6 times as compared to the TENG without CS deposition on it. From parametric studies, the TENG using the cold-sprayed composite layer produced an electrical potential of 1140 V for a simple structure with a 25.4 × 25.4 mm2 contact area. We also optimize the geometry and fabrication process of the TENG to increase the manufacturing efficiency while reducing the processing cost. The resultant sprayed layers and structures exhibited sustainable robustness by showing consistent electrical performance after the mechanical adhesion test. The proposed manufacturing approach is also applicable for processing three-dimensional (3D) complex layers owing to the technological convergence of a cold spray gun attached to a robotic arm, which makes possible to fabricate the 3D TENG. To elaborate, a composite layer having the shape of a 3D ball is produced, and the exercise status of the ball is monitored in real-time. The fabricated 3D ball using the TENG transmitted a distinguishable signal in real-time according to the state of the ball. The proposed TENG sensing system can be utilized as a self-powered sensor without the need of a battery, amplifier, and rectifier. The results of this study can potentially provide insights for the practical material design and fabrication of self-powered TENG systems.

A Programmable Dual-Regime Spray for Large-Scale and Custom-Designed Electronic Textiles.

Increasing demand for wearable healthcare synergistically advances the field of electronic textiles, or e-textiles, allowing for ambulatory monitoring of vital health signals. Despite great promise, the pragmatic deployment of e-textiles in clinical practice remains challenged due to the lack of a method in producing custom-designed e-textiles at high spatial resolution across a large area. To this end, a programmable dual-regime spray that enables the direct custom writing of functional nanoparticles into arbitrary fabrics at sub-millimeter resolution over meter scale is employed. The resulting e-textiles retain the intrinsic fabric properties in terms of mechanical flexibility, water-vapor permeability, and comfort against multiple uses and laundry cycles. The e-textiles tightly fit various body sizes and shapes to support the high-fidelity recording of physiological and electrophysiological signals on the skin under ambulatory conditions. Pilot field tests in a remote health-monitoring setting with a large animal, such as a horse, demonstrate the scalability and utility of the e-textiles beyond conventional devices. This approach will be suitable for the rapid prototyping of custom e-textiles tailored to meet various clinical needs.

Effect of Au-Coating on the Laser Spot Cutting on Spring Contact Probe (SCP) for Semi-Conductor Inspection.

Spring contact probes (SCPs) are used to make contact with various test points on printed circuit boards (PCBs), wire harnesses, and connectors. Moreover, they can consist of the test interface between the PCBs and the semiconductor devices. For mass production of SCPs, ultra-small precision components have been manufactured by conventional cutting methods. However, these cutting methods adversely affect the performance of components due to tool wear and extreme shear stress at the contact point. To solve this problem, laser spot cutting is applied to Au-coated SCP specimens as an alternative technique. A 20 W nano-second pulsed Ytterbium fiber laser is used, and the experimental variables are different laser parameters including the pulse duration and repetition rate. After the spot cutting experiments, the heat-affected zone (HAZ) and material removal zone (MRZ) formed by different total irradiated energy (Etotal) was observed by using a scanning electron microscope (SEM). Then, the size of HAZ, top and bottom parts of MRZ, and roundness were measured. Furthermore, the change rate of HAZ and MRZ on Au-coated and non-coated specimens was analyzed with regard to different pulse durations. Based on these results, the effect of Au-coating on the SCP was evaluated through the comparison with the non-coated specimen. Consequently, in the Au-coated specimen, hole penetration was observed at a low pulse duration and low total energy due to the higher thermal conductivity of Au. From this study, the applicability of laser spot cutting to Au-coated SCP is investigated.

Milling Performance of CFRP Composite and Atomised Vegetable Oil as a Function of Fiber Orientation.

Carbon fiber reinforced polymers (CFRPs) have found diverse applications in the automotive, space engineering, sporting goods, medical and military sectors. CFRP parts require limited machining such as detouring, milling and drilling to produce the shapes used, or for assembly purposes. Problems encountered while machining CFRP include poor tool performance, dust emission, poor part edge quality and delamination. The use of oil-based metalworking fluid could help improve the machining performance for this composite, but the resulting humidity would deteriorate the structural integrity of the parts. In this work the performance of an oil-in-water emulsion, obtained using ultrasonic atomization but no surfactant, is examined during the milling of CFRP in terms of fiber orientation and milling feed rate. The performance of wet milling is compared with that of a dry milling process. The tool displacement-fiber orientation angles (TFOA) tested are 0°, 30°, 45°, 60°, and 90°. The output responses analyzed were cutting force, delamination, and tool wear. Using atomized vegetable oil helps in significantly reducing the cutting force, tool wear, and fiber delamination as compared to the dry milling condition. The machining performance was also strongly influenced by fiber orientation. The interactions between the fiber orientation, the machining parameters and the tested vegetable oil-based fluid could help in selecting appropriate cutting parameters and thus improve the machined part quality and productivity.

Biomaterial Strategies for Delivering Stem Cells as a Treatment for Spinal Cord Injury.

Ongoing clinical trials are evaluating the use of stem cells as a way to treat traumatic spinal cord injury (SCI). However, the inhibitory environment present in the injured spinal cord makes it challenging to achieve the survival of these cells along with desired differentiation into the appropriate phenotypes necessary to regain function. Transplanting stem cells along with an instructive biomaterial scaffold can increase cell survival and improve differentiation efficiency. This study reviews the literature discussing different types of instructive biomaterial scaffolds developed for transplanting stem cells into the injured spinal cord. We have chosen to focus specifically on biomaterial scaffolds that direct the differentiation of neural stem cells and pluripotent stem cells since they offer the most promise for producing the cell phenotypes that could restore function after SCI. In terms of biomaterial scaffolds, this article reviews the literature associated with using hydrogels made from natural biomaterials and electrospun scaffolds for differentiating stem cells into neural phenotypes. It then presents new data showing how these different types of scaffolds can be combined for neural tissue engineering applications and provides directions for future studies.

Numerical Approach to Modeling and Characterization of Refractive Index Changes for a Long-Period Fiber Grating Fabricated by Femtosecond Laser.

A 3D finite element model constructed to predict the intensity-dependent refractive index profile induced by femtosecond laser radiation is presented. A fiber core irradiated by a pulsed laser is modeled as a cylinder subject to predefined boundary conditions using COMSOL5.2 Multiphysics commercial package. The numerically obtained refractive index change is used to numerically design and experimentally fabricate long-period fiber grating (LPFG) in pure silica core single-mode fiber employing identical laser conditions. To reduce the high computational requirements, the beam envelope method approach is utilized in the aforementioned numerical models. The number of periods, grating length, and grating period considered in this work are numerically quantified. The numerically obtained spectral growth of the modeled LPFG seems to be consistent with the transmission of the experimentally fabricated LPFG single mode fiber. The sensing capabilities of the modeled LPFG are tested by varying the refractive index of the surrounding medium. The numerically obtained spectrum corresponding to the varied refractive index shows good agreement with the experimental findings.

Electrospun biomaterial scaffolds with varied topographies for neuronal differentiation of human-induced pluripotent stem cells.

In this study, we investigated the effect of micro and nanoscale scaffold topography on promoting neuronal differentiation of human induced pluripotent stem cells (iPSCs) and directing the resulting neuronal outgrowth in an organized manner. We used melt electrospinning to fabricate poly (ε-caprolactone) (PCL) scaffolds with loop mesh and biaxial aligned microscale topographies. Biaxial aligned microscale scaffolds were further functionalized with retinoic acid releasing PCL nanofibers using solution electrospinning. These scaffolds were then seeded with neural progenitors derived from human iPSCs. We found that smaller diameter loop mesh scaffolds (43.7 ± 3.9 µm) induced higher expression of the neural markers Nestin and Pax6 compared to thicker diameter loop mesh scaffolds (85 ± 4 µm). The loop mesh and biaxial aligned scaffolds guided the neurite outgrowth of human iPSCs along the topographical features with the maximum neurite length of these cells being longer on the biaxial aligned scaffolds. Finally, our novel bimodal scaffolds also supported the neuronal differentiation of human iPSCs as they presented both physical and chemical cues to these cells, encouraging their differentiation. These results give insight into how physical and chemical cues can be used to engineer neural tissue.