Structure-Foldable and Performance-Tailorable PI Paper-Based Triboelectric Nanogenerators Processed and Controlled by Laser-Induced Graphene.

Laser-induced graphene (LIG) technology has provided a new manufacturing strategy for the rapid and scalable assembling of triboelectric nanogenerators (TENG). However, current LIG-based TENG commonly rely on polymer films, e.g., polyimide (PI) as both friction material and carbon precursor of electrodes, which limit the structural diversity and performance escalation due to its incapability of folding and creasing. Using specialized PI paper composed of randomly distributed PI fibers to substantially enhance its foldability, this work creates a new type of TENG, which are structurally foldable and stackable, and performance tailorable. First, by systematically investigating the laser power-regulated performance of single-unit TENG, the open-circuit voltage can be effectively improved. By further exploiting the folding process, multiple TENG units can be assembled together to form multi-layered structures to continuously expand the open-circuit voltage from 5.3 to 34.4 V cm-2, as the increase of friction units from 1 to 16. Last, by fully utilizing the unique structure and performance, representative energy-harvesting and smart-sensing applications are demonstrated, including a smart shoe to recognize running motions and power LEDs, a smart leaf to power a thermometer by wind, a matrix sensor to recognize writing trajectories, as well as a smart glove to recognize different objects.

Correction: Kirigami-enabled stretchable laser-induced graphene heaters for wearable thermotherapy.

Correction for 'Kirigami-enabled stretchable laser-induced graphene heaters for wearable thermotherapy' by Junyu Chen et al., Mater. Horiz., 2024, 11, 2010-2020, https://doi.org/10.1039/D3MH01884A.

Kirigami-enabled stretchable laser-induced graphene heaters for wearable thermotherapy.

Flexible and stretchable heaters are increasingly recognized for their great potential in wearable thermotherapy to treat muscle spasms, joint injuries and arthritis. However, issues like lengthy processing, high fabrication cost, and toxic chemical involvement are obstacles on the way to popularize stretchable heaters for medical use. Herein, using a single-step customizable laser fabrication method, we put forward the design of cost-effective wearable laser-induced graphene (LIG) heaters with kirigami patterns, which offer multimodal stretchability and conformal fit to the skin around the human body. First, we develop the manufacturing process of the LIG heaters with three different kirigami patterns enabling reliable stretchability by out-of-plane buckling. Then, by adjusting the laser parameters, we confirm that the LIG produced by medium laser power could maintain a balance between mechanical strength and electrical conductivity. By optimizing cutting-spacing ratios through experimental measurements of stress, resistance and temperature profiles, as well as finite element analysis (FEA), we determine that a larger cutting-spacing ratio within the machining precision will lead to better mechanical, electrical and heating performance. The optimized stretchable heater in this paper could bear significant unidirectional strain over 100% or multidirectional strain over 20% without major loss in conductivity and heating performance. On-body tests and fatigue tests also proved great robustness in practical scenarios. With the advantage of safe usage, simple and customizable fabrication, easy bonding with skin, and multidirectional stretchability, the on-skin heaters are promising to substitute the traditional heating packs/wraps for thermotherapy.

Ultrasensitive Humidity Sensors with Synergy between Superhydrophilic Porous Carbon Electrodes and Phosphorus-Doped Dielectric Electrolyte.

Capacitive humidity sensors have been used for human health monitoring, but their performance may be poor in terms of sensitivity and response time, because of limitations in sensing materials and insufficient knowledge about sensing mechanisms. Herein, a new combination of humidity sensing materials to assemble thin-film based capacitive-type sensors is proposed by using PA-doped polybenzimidazole (PA-PBI) as an electrolyte and laser-carbonized PA-PBI as a carbon electrode (PA-PBI-C). Based on PA involved laser scribing, the flexible sensor can reach excellent humidity-sensing performances with an ultrahigh sensitivity (1.16 × 106 pF RH%-1, where RH represents the relative humidity), a superior linearity (R2 = 0.9982), a fast response time (0.72 s), and a low hysteresis in a wide RH range from 1% to 95%. By further studying P-O decorated porous carbon electrode with superhydrophilicity and the solid-state dielectric electrolyte featured by a high dielectric constant, a synergistic sensing mechanism consisting of a "Water reservoir" and a "Bridge" is established to support advanced health-monitoring applications such as the respiration patterns and skin condition where both sensitivity and response time are critical.

Laser-Induced Graphene Enabled Additive Manufacturing of Multifunctional 3D Architectures with Freeform Structures.

3D printing has become an important strategy for constructing graphene smart structures with arbitrary shapes and complexities. Compared with graphene oxide ink/gel/resin based manners, laser-induced graphene (LIG) is unique for facile and scalable assembly of 1D and 2D structures but still faces size and shape obstacles for constructing 3D macrostructures. In this work, a brand-new LIG based additive manufacturing (LIG-AM) protocol is developed to form bulk 3D graphene with freeform structures without introducing extra binders, templates, and catalysts. On the basis of selective laser sintering, LIG-AM creatively irradiates polyimide (PI) powder-bed for triggering both particle-sintering and graphene-converting processes layer-by-layer, which is unique for assembling varied types of graphene architectures including identical-section, variable-section, and graphene/PI hybrid structures. In addition to exploring combined graphitizing and fusing discipline, processing efficiency and assembling resolution of LIG-AM are also balanceable through synergistic control of lasing power and powder-feeding thickness. By further studying various process dependent properties, a LIG-AM enabled aircraft-wing section model is finally printed to comprehensively demonstrate its shiftable process, hybridizable structure, and multifunctional performance including force-sensing, anti-icing/deicing, and microwave shielding and absorption.

3D-Laminated Graphene with Combined Laser Irradiation and Resin Infiltration toward Designable Macrostructure and Multifunction.

Macroscopic 3D graphene has become a significant topic for satisfying the continuously upgraded smart structures and devices. Compared with liquid assembling and catalytic templating methods, laser-induced graphene (LIG) is showing facile and scalable advantages but still faces limited sizes and geometries by using template induction or on-site lay-up strategies. In this work, a new LIG protocol is developed for facile stacking and shaping 3D LIG macrostructures by laminating layers of LIG papers (LIGPs) with combined resin infiltration and hot pressing. Specifically, the constructed 3D LIGP composites (LIGP-C) are compatible with large area, high thickness, and customizable flat or curved shapes. Additionally, systematic research is explored for investigating critical processing parameters on tuning its multifunctional properties. As the laminated layers are stacked from 1 to 10, it is discovered that piezoresistivity (i.e., gauge factor) of LIGP-C dramatically reflects an ≈3900% improvement from 0.39 to 15.7 while mechanical and electrical properties maintain simultaneously at the highest levels, attributed to the formation of densely packed fusion layers. Along with excellent durability for resisting multiple harsh environments, a sensor-array system with 5 × 5 LIGP-C elements is finally demonstrated on fiber-reinforced polymeric composites for accurate strain mapping.

Decisions on train rescheduling and locomotive assignment during the COVID-19 outbreak: A case of the Beijing-Tianjin intercity railway.

Travel restriction measures have been widely implemented to curb the continued spread of COVID-19 during the Chinese Lunar New Year celebrations. Many operation lines and train schedules of China's railway were either heavily adjusted or canceled. In this study, a mixed-integer linear programming model and a two-step solution algorithm were developed to handle such large-scale adjustments. The formulation considers a flexible time window for each operation line and locomotive traction operations, and minimizes the number of locomotives utilized with their total idle time for train rescheduling and locomotive assignment, respectively. The solution algorithm determines the minimum locomotive fleet size based on the optimal train rescheduling results; it then reduces the traction idle time of locomotives. In response to the uncertainty of COVID-19, two tailored approaches were also designed to recover and remove operation lines, which can insert and cut operation lines based on the results of locomotive assignment. Finally, we conducted a case study of the Beijing-Tianjin intercity railway from the start of the COVID-19 outbreak to the recovery of operations.

Multifunctional Laser-Induced Graphene Papers with Combined Defocusing and Grafting Processes for Patternable and Continuously Tunable Wettability from Superlyophilicity to Superlyophobicity.

Functional surfaces with tunable and patternable wettability have attracted significant research interests because of remarkable advantages in biomedicine, environmental, and energy storage applications. Based on combined defocusing and grafting strategy for processing laser-induced graphene papers (LIGPs) with variable surface roughness (58.18-6.08 µm) and F content (0-25.9%), their wettability can be tuned continuously from superlyophilicity (contact angle CA ≈ 0° ) to superlyophobicity (CA > 150° ), for various liquids with a wide range of surface tensions from 27.5 to 72.8 mN m-1 . In addition to reaching multiple wetting characteristics including amphiphilic, amphiphobic, and hydrophobic-oleophilic states, three designable processes are further developed for achieving LIGPs with various wetting patterns, including hydrophilic arrays or channels, hydrophobic-to-hydrophilic gradients, and Janus. Activated by the customly designed structures and properties, multifunctional and multi-scenario applications are successfully attempted, including 2D-/3D- directional cell cultivation, water transportation diode, self-triggered liquid transfer & collection, etc.

A New Route to Enhance the Packing Density of Buckypaper for Superior Piezoresistive Sensor Characteristics.

Transforming individual carbon nanotubes (CNTs) into bulk form is necessary for the utilization of the extraordinary properties of CNTs in sensor applications. Individual CNTs are randomly arranged when transformed into the bulk structure in the form of buckypaper. The random arrangement has many pores among individual CNTs, which can be treated as gaps or defects contributing to the degradation of CNT properties in the bulk form. A novel technique of filling these gaps is successfully developed in this study and termed as a gap-filling technique (GFT). The GFT is implemented on SWCNT-based buckypaper in which the pores are filled through small-size MWCNTs, resulting in a ~45.9% improvement in packing density. The GFT is validated through the analysis of packing density along with characterization and surface morphological study of buckypaper using Raman spectrum, particle size analysis, scanning electron microscopy, atomic force microscopy and optical microscopy. The sensor characteristics parameters of buckypaper are investigated using a dynamic mechanical analyzer attached with a digital multimeter. The percentage improvement in the electrical conductivity, tensile gauge factor, tensile strength and failure strain of a GFT-implemented buckypaper sensor are calculated as 4.11 ± 0.61, 44.81 ± 1.72, 49.82 ± 8.21 and 113.36 ± 28.74, respectively.

Laser-Induced Graphene Paper Heaters with Multimodally Patternable Electrothermal Performance for Low-Energy Manufacturing of Composites.

Low-energy manufacturing of polymeric composites through two-dimensional electrothermal heaters is a promising strategy over the traditional autoclave and oven. Laser-induced graphene paper (LIGP) is a recent emergent multifunctional material with the merits of one-step computer aided design and manufacturing (CAD/CAM) as well as a flexible thin nature. To fully explore its capabilities of in situ heating, herein, we adventurously propose and investigate the customizable manufacture and modulation of LIGP enabled heaters with multimodally patternable performance. Developed by two modes (uniform and nonuniform) of laser processing, the LIGP heaters (LIGP-H) show distinctively unique characteristics, including high working range (>600 °C), fast stabilization (<8 s), high temperature efficiency (∼370 °C·cm2/W), and superb robustness. Most innovatively, the nonuniform processing could section LIGP-H into subzones with independently controlled heating performance, rendering various designable patterns. The above unique characteristics guarantee the LIGP-H to be highly reliable for in situ curing composites with flat, curved, and even inhomogeneous structures. With enormous energy-savings (∼85%), superb curing accuracy, and comparable mechanical strength, the proposed device is advantageous for assuring high-quality and highly efficient manufacturing.

Stretchable Graphene Thin Film Enabled Yarn Sensors with Tunable Piezoresistivity for Human Motion Monitoring.

1D graphene based flexible sensors as wearable electronics have recently attracted considerable attentions because of lightweight, high extensibility, easy to wind and weave, and superior sensitivity. In this research, we established a facile and low-cost strategy to construct graphene thin film enabled yarn sensors (GYS) by combining the process of graphene oxide (GO) coating and reducing on polyester (PE) wound spandex yarns. According to systematic processing-property relationship study, a key finding of this work discovers that the degree of resistance recovery as well as gauge sensitivity of GYS can be well controlled and modulated by a pre-stretch treatment. Specifically, as the level of pre-stretch increases from 0 to 60%, the deformable range of sensor that guarantees full resistance recovery prolongs evidently from 0% to ~50%. Meanwhile, the gauge factor of GYS is tunable in the range from 6.40 to 12.06. To understand the pre-stretch process dependent sensing performance, SEM analysis was assisted to evidence the growing size of micro-cracks determining dominantly the behavior of electron transport. Lastly, to take better advantage of GYS, a new wearing mode was demonstrated by direct winding the yarn sensor on varied portions of human body for monitoring different body movements and muscle contracting & relaxing.

Micro-Crack Induced Buckypaper/PI Tape Hybrid Sensors with Enhanced and Tunable Piezo-Resistive Properties.

Piezoresistive properties play a vital role in the development of sensor for structural health monitoring (SHM) applications. Novel stable crack initiation method (SCIM) is established to improve the gauge factor (GF) with maximum achievable working strain region for PI tape enabled buckypaper hybrid sensors. Cracks are generated by applying strain rate-controlled tension force using dynamic mechanical analyzer (DMA). The sensor has been cycled in tension to characterize GF with crack opening. It is determined experimentally that GF increases with increasing crack opening and crack becomes unstable when opening increases above 8 µm. Tremendous improvement in GF has been observed which improved from single-digit to several hundreds. The highest GF obtained so far is ~255, showing 75 times improvement compared with the ones without the SCIM implementation. The crack initiation strain (CIS) is characterized by sonication and centrifugation time. It is determined experimentally that the maximum CIS of 3.5% can be achieved with sonication time of 40 min and increasing centrifuge time has an in-significantly dropping effect on CIS. Excellent stability/reproducibility has been proved/demonstrated on SCIM implemented sensors through a rigorous 12,500 tensile cycle test on DMA. The performance of sensor is practically demonstrated in tension and bending on glass fiber reinforced polymer (GFRP) structures.

Harnessing the layer-by-layer assembly technique to design biomaterials vaccines for immune modulation in translational applications.

The existence of challenging diseases such as cancers, HIV and Zika requires developing new vaccines that can generate tunable and robust immune responses against the diseases. Biomaterials-based techniques have been broadly explored for designing vaccines that can produce controllable and potent immunity. Among the existing biomaterials-based strategies, the layer-by-layer (LbL) assembly technique is remarkably attractive in vaccine design due to its unique features such as programmed and versatile cargo loading, cargo protection, co-delivery, juxtaposing of immune signals, etc. In this work, we reviewed the existing LbL-based vaccine design techniques for translational applications. Specifically, we discussed nanovaccines constructed by coating polyelectrolyte multilayers (PEMs) on nanoparticles, microcapsule vaccines assembled from PEMs, polyplex/complex vaccines condensed from charged materials and microneedle vaccines deposited with PEMs, highlighting the employment of these techniques to promote immunity against diseases ranging from cancers to infectious and autoimmune diseases (i.e., HIV, influenza, multiple sclerosis, etc.). Additionally, the review specifically emphasized using LbL-based vaccine technologies for tuning the cellular and molecular pathways, demonstrating the unique advantages presented by these vaccination strategies. These studies showed the versatility and potency of using LbL-based techniques for designing the next generation of biomaterials vaccines for translational purposes.

Carbon Nanomaterials Based Smart Fabrics with Selectable Characteristics for In-Line Monitoring of High-Performance Composites.

Carbon nanomaterials have gradually demonstrated their superiority for in-line process monitoring of high-performance composites. To explore the advantages of structures, properties, as well as sensing mechanisms, three types of carbon nanomaterials-based fiber sensors, namely, carbon nanotube-coated fibers, reduced graphene oxide-coated fibers, and carbon fibers, were produced and used as key sensing elements embedded in fabrics for monitoring the manufacturing process of fiber-reinforced polymeric composites. Detailed microstructural characterizations were performed through SEM and Raman analyses. The resistance change of the smart fabric was monitored in the real-time process of composite manufacturing. By systematically analyzing the piezoresistive performance, a three-stage sensing behavior has been achieved for registering resin infiltration, gelation, cross-linking, and post-curing. In the first stage, the incorporation of resin expands the packing structure of various sensing media and introduces different levels of increases in the resistance. In the second stage, the concomitant resin shrinkage dominates the resistance attenuation after reaching the maximum level. In the last stage, the diminished shrinkage effect competes with the disruption of the conducting network, resulting in continuous rising or depressing of the resistance.

Laser-Induced Freestanding Graphene Papers: A New Route of Scalable Fabrication with Tunable Morphologies and Properties for Multifunctional Devices and Structures.

The recently emergent laser-induced graphene (LIG) technology has endowed the fabrication of smart devices with one-step processing and scalable/designable features. Graphene paper (GP), an important architecture of 2D layered carbon, however, is never produced through LIG. Herein, a novel strategy is reported for production of freestanding GP through LIG technology. It is first determined that the unique spatial configuration of polyimide (PI) paper is critical for the preparation of GP without the appearance of intense shape distortion. Benefiting from the mechanism, the as-produced laser-induced graphene paper (LIGP) is foldable, trimmable, and integratable to customized shapes and structures with the largest dimension of 40 × 35 cm2 . Based on the processing-structure-property relationship study, one is capable of controlling and tuning various physical and chemical properties of LIGPs, rendering them unique for assembling flexible electronics and smart structures, e.g., human/robotic motion detectors, liquid sensors, water-oil separators, antibacterial media, and flame retardant/deicing/self-sensing composites. With the key findings, the escalation of LIGP for commercialization, roll-to-roll manufacturing, and multidisciplinary applications are highly expected.

Generation of Well-Defined Micro/Nanoparticles via Advanced Manufacturing Techniques for Therapeutic Delivery.

Micro/nanoparticles have great potentials in biomedical applications, especially for drug delivery. Existing studies identified that major micro/nanoparticle features including size, shape, surface property and component materials play vital roles in their in vitro and in vivo applications. However, a demanding challenge is that most conventional particle synthesis techniques such as emulsion can only generate micro/nanoparticles with a very limited number of shapes (i.e., spherical or rod shapes) and have very loose control in terms of particle sizes. We reviewed the advanced manufacturing techniques for producing micro/nanoparticles with precisely defined characteristics, emphasizing the use of these well-controlled micro/nanoparticles for drug delivery applications. Additionally, to illustrate the vital roles of particle features in therapeutic delivery, we also discussed how the above-mentioned micro/nanoparticle features impact in vitro and in vivo applications. Through this review, we highlighted the unique opportunities in generating controllable particles via advanced manufacturing techniques and the great potential of using these micro/nanoparticles for therapeutic delivery.

CNT Enabled Co-braided Smart Fabrics: A New Route for Non-invasive, Highly Sensitive &Large-area Monitoring of Composites.

The next-generation of hierarchical composites needs to have built-in functionality to continually monitor and diagnose their own health states. This paper includes a novel strategy for in-situ monitoring the processing stages of composites by co-braiding CNT-enabled fiber sensors into the reinforcing fiber fabrics. This would present a tremendous improvement over the present methods that excessively focus on detecting mechanical deformations and cracks. The CNT enabled smart fabrics, fabricated by a cost-effective and scalable method, are highly sensitive to monitor and quantify various events of composite processing including resin infusion, onset of crosslinking, gel time, degree and rate of curing. By varying curing temperature and resin formulation, the clear trends derived from the systematic study confirm the reliability and accuracy of the method, which is further verified by rheological and DSC tests. More importantly, upon wisely configuring the smart fabrics with a scalable sensor network, localized processing information of composites can be achieved in real time. In addition, the smart fabrics that are readily and non-invasively integrated into composites can provide life-long structural health monitoring of the composites, including detection of deformations and cracks.

Features of the Asynchronous Correlation between the China Coal Price Index and Coal Mining Accidental Deaths.

The features of the asynchronous correlation between accident indices and the factors that influence accidents can provide an effective reference for warnings of coal mining accidents. However, what are the features of this correlation? To answer this question, data from the China coal price index and the number of deaths from coal mining accidents were selected as the sample data. The fluctuation modes of the asynchronous correlation between the two data sets were defined according to the asynchronous correlation coefficients, symbolization, and sliding windows. We then built several directed and weighted network models, within which the fluctuation modes and the transformations between modes were represented by nodes and edges. Then, the features of the asynchronous correlation between these two variables could be studied from a perspective of network topology. We found that the correlation between the price index and the accidental deaths was asynchronous and fluctuating. Certain aspects, such as the key fluctuation modes, the subgroups characteristics, the transmission medium, the periodicity and transmission path length in the network, were analyzed by using complex network theory, analytical methods and spectral analysis method. These results provide a scientific reference for generating warnings for coal mining accidents based on economic indices.

Versatile surface micropatterning and functionalization enabled by microcontact printing of poly(4-aminostyrene).

Microcontact printing (µCP) of polyelectrolytes is a facile and powerful method for surface micro/nanopatterning and functionalization. Poly(4-aminostyrene) (PAS) is a polyelectrolyte that can be converted to aryldiazonium salt and exhibits pH-dependent hydrophobicity. Here we demonstrate µCP of PAS and the expansion of this technique in various directions. First, the microcontact-printed PAS can be diazotized to micropattern biomolecules including DNA and protein and nanomaterials including single-walled carbon nanotubes and gold nanoparticles. Second, the diazotized PAS enables µCP of a metallic structure on a carbon surface. Third, the hydrophobic nature of PAS at the neutral pH allows the microcontact-printed PAS-based polyelectrolyte multilayer to be used as masks for wet etching. Lastly, this technique allows facile fabrication of highly engineered microparticles with a unique structure. Overall, this work has established a novel µCP platform with various potential applications.

Graphite nanoplatelet enabled embeddable fiber sensor for in situ curing monitoring and structural health monitoring of polymeric composites.

A graphite nanoplatelet (GNP) thin film enabled 1D fiber sensor (GNP-FibSen) was fabricated by a continuous roll-to-roll spray coating process, characterized by scanning electron microscopy and Raman spectroscopy and evaluated by coupled electrical-mechanical tensile testing. The neat GNP-FibSen sensor shows very high gauge sensitivity with a gauge factor of ∼17. By embedding the sensor in fiberglass prepreg laminate parts, the dual functionalities of the GNP-FibSen sensor were demonstrated. In the manufacturing process, the resistance change of the embedded sensor provides valuable local resin curing information. After the manufacturing process, the same sensor is able to map the strain/stress states and detect the failure of the host composite. The superior durability of the embedded GNP-FibSen sensor has been demonstrated through 10,000 cycles of coupled electromechanical tests.