Properties Of Ink Research Articles

Characteristics of Food Printing Inks and Their Impact on Selected Product Properties

Three-dimensional printing, or additive manufacturing, produces three-dimensional objects using a digital model. Its utilisation has been observed across various industries, including the food industry. Technology offers a wide range of possibilities in this field, including creating innovative products with unique compositions, shapes, and textures. A significant challenge in 3D printing is the development of the optimal ink composition. These inks must possess the appropriate rheology and texture for printing and meet nutritional and sensory requirements. The rheological properties of inks play a pivotal role in the printing process, influencing the formation of stable structures. This article comprehensively characterises food inks, distinguishing two primary categories and their respective subgroups. The first category encompasses non-natively extrudable inks, including plant-based inks derived from fruits and vegetables and meat-based inks. The second category comprises natively extrudable inks, encompassing dairy-based, hydrogel-based, and confectionary-based inks. The product properties of rheology, texture, fidelity, and printing stability are then discussed. Finally, the innovative use of food inks is shown.

Direct Ink Writing and Photocrosslinking of Hydroxypropyl Cellulose into Stable 3D Parts Using Methacrylation and Blending

Two 50% solid content solutions of methacrylated hydroxypropyl cellulose (MAHPC) with respective substitution degrees of 1.85 ± 0.04 (L_MAHPC) and 2.64 ± 0.04 (H_MAHPC) were screened for rheological properties, photocrosslinking kinetics and printability in relevance to direct ink writing (DIW). Photo-rheological and printability studies reveal that the rheological properties of both MAHPC inks are better suited for DIW than those of hydroxypropyl cellulose (HPC) inks. Namely, methacrylate grafting improves shear dynamic moduli at low strain but also shear thinning and shear recovery. Both inks completely cure within 30 s upon shining UV light. Photocrosslinking is found to follow the phenomenological autocatalytic Sestak–Berggren kinetic model. However, prolonged exposure to UV light past full cure upon DIW leads to part fracture. The narrow UV-cure time window consequently precludes the production of multilayer parts using UV-assisted DIW for these neat MAHPC inks. In contrast, when blending MAHPC with HPC, an optimal balance between curing kinetics and DIW conditions is achieved, and stable, high-fidelity 150-layered parts are produced. Altogether this research highlights the need to design the content of photocrosslinkable moieties of cellulose derivatives to photoprint high fidelity and stable 3D parts from HPC inks.

Reversible Thixotropic Rheological Properties of Graphene-Incorporated Epoxy Inks for Self-Standing 3D Printing.

As three-dimensional (3D) printing has emerged as a new manufacturing technology, the demand for high-performance 3D printable materials has increased to ensure broad applicability in various load-bearing structures. In particular, the thixotropic properties of materials, which allow them to flow under applied external forces but resist flowing otherwise, have been reported to enable rapid and high-resolution printing owing to their self-standing and easily processable characteristics. In this context, graphene nanosheets exhibit unique π-π stacking interactions between neighboring sheets, likely imparting self-standing capability to low-viscosity inks. Herein, we develop a thermally curable graphene-incorporated epoxy ink system that exhibits shear-thinning characteristics and upright standing capability owing to its high static yield stress (∼1,680 Pa). The reversible liquid-to-solid phase transition of the composite ink, absent in the pristine epoxy ink, is clearly identified by its viscoelastic properties and dynamic yield stress. This thixotropic composite ink enables the continuous filament printing of 10 stacked layers without the spreading of injected filaments. Significantly, the 3D-printed composite structure, post-thermal curing, exhibits robust structural integrity and is free from weld lines or voids at the stacked interfaces. Combined with the clearly elucidated processing-structure-property relationships of the ink system, our results highlight its potential for a wide spectrum of applications.

Tuning Printability and Adhesion of a Silver-Based Ink for High-Performance Strain Gauges Manufactured via Direct Ink Writing.

Structural health monitoring (SHM) systems are critical in ensuring the safety of space exploration, as spacecraft and structures can experience detrimental stresses and strains. By deploying conventional strain gauges, SHM systems can promptly detect and assess localized strain behaviors in structures; however, these strain gauges are limited by low sensitivity (gauge factor, GF ∼ 2). This study introduces an approach to printing strain gauges with high sensitivity, while also considering stretchability and long-term durability. Through direct ink writing (DIW), these devices can be produced by the extrusion of a wide range of viscoelastic inks. The viscoelastic properties of the ink can be tuned with the help of additives to aid in the processing for a desired application. In this work, a series of inks were prepared from commercially available CB028 (silver ink used in screen printing) by adding a combination of ethyl cellulose (EC) and polyolefin (PO) (additives). With the goal of optimizing the long-term sensing response of the printed strain gauges, a systematic study of the rheological properties (frequency sweep analyses, yield stress, viscoelastic recovery, viscosity measurements, and tack tests) was conducted. A viscoelastic window approach was used to predict the optimal properties of the formulated inks. Using this approach, it was determined that 90% CB028, 5% EC, and 5% PO provided enhanced elastic properties, adhesion, and peel strength compared to commercial CB028. The formulated ink has enhanced tack (129 mN/mm2) and peel strength (23.3 kJ/mm2), which led to a viscoelastic window ideal for direct ink writing of the strain gauges. Printed structures were tested in a three-point bending configuration to record the piezoresistive responses that were correlated to the formulated rheological properties and underlying microstructure. The results revealed gauge factors as high as 106 with stable sensing responses for more than 300 cycles of strain. Scanning electron microscopy analysis also revealed minimal crack formation, which resulted in a stable response. The research demonstrated the feasibility of developing high-performance inks for potential printed strain gauge applications.

Optimised properties of conductive polyaniline-polyvinyl alcohol ink painted on paper for ductile pressure sensor with reduced electrical drift

Polyaniline (PANI) powder in its emeraldine salt form was blended with various concentrations of polyvinyl alcohol (PVA) to create semiconducting inks with desired fluid properties. These inks were coated on cellulose paper, and their resistive responses were tested under different vacuum pressures. Enhanced conductivity and reduced creep behavior were achieved by incorporating an O–H bond between the H of PANI and O of PVA, which stabilizes the polymer structure. This bonding minimizes electrical drift, improving the reliability of the synthesized inks for applications such as designing flexible circuits and fabricating thermoelectric generators. The strain field developed under vacuum is accountable for the observed variation in electrical properties. Due to the increase in strain field, the polaron hopping barrier increases, and as a result, the effective conductivity decreases with a decrease in pressure. These ‘use-and-throw’ sensors are economical, adaptable, and environmentally friendly, ideal for various disposable electronics and sensing applications.

In Situ Scanning Electron Microscopy Crack Characterization and Resistance Evolution in Cyclically-Strained Ag Nanoflake-Based Inks.

The reliability of nanocomposite conductive inks under cyclic loading is the key to designing robust flexible electronics. Although resistance increases with cycling and models exist, the exact degradation mechanism is not well understood and is critical for developing inks. This study links cracking behavior to changes in electrical resistance by performing in situ cyclic stretch experiments in scanning electron microscopy (SEM) with synchronized resistance measurements. Two screen-printed conductive inks, PE874 and 5025, on thermoplastic polyurethane (TPU) and polyimide (PI) substrates, respectively, were tested using the in situ technique. The obtained SEM images were analyzed with digital image correlation (DIC) to map the strain across cycles. The strain maps show that fatigue damage mainly occurred within the cracks formed during the initial monotonic stretch. There was no delamination at the ink-substrate interface or crack extension along the surface with cycling. Instead, fatigue damage resulted from a combination of crack widening and local shearing within the existing cracks. Crack depth varied based on the ink and substrate properties. The cracks in the 5025 ink on the PI substrate were only partially through the ink thickness, while fully through-thickness cracks were more prevalent in the PE874 ink on the TPU substrate. The 5025 ink showed a faster resistance increase with cycling than the PE874 ink because fatigue damage affected more bridging ink material for partial through-thickness cracks. Higher strain amplitudes caused greater crack widening and shearing and therefore faster resistance increase per cycle.

Preparation of a New Formulation of Hybrid GNP/Ag Conductive Ink with a Specific Ratio of Organic Solvent

This paper presents the preparation of a new formulation of hybrid GNP/Ag conductive ink with a specific ratio of organic solvent to optimize the properties of hybrid conductive ink. The GNP/Ag hybrid conductive ink was formed with a different ratio of organic solvents which are 33:67,60:40,67:33 and 40:60 of 1-butanol to terpinol which the ratio of conductive filler is higher than the organic solvent. The performance of each ink was examined in terms of bulk resistance and resistivity where the conductive ink was prepared on the copper substrate and cured for five hours in the oven at a temperature of 250°C and underwent a cyclic bending test. Results indicate that the 40:60 ratio of 1-butanol to terpinol is the best ratio for GNP/Ag hybrid conducive ink with a bulk resistance of 0.600Ω and resistivity of 3.6x10-4Ωm. For further exploration, the curing time should remain five hours at a different curing temperature.

Simple and Cost-effective Fabrication of a Supercapacitor Using Carbon Nanoparticle-based Ink

The demand for energy storage devices such as supercapacitors is rapidly increasing in most applications, including electric transportation and portable electronics. The material's high cost and the fabrication complexity of supercapacitors suppress their mass production. In this research, a commercial low-cost conductive ink has been simply painted on flexible stainless steel sheets as supercapacitor electrodes. The ink is mainly based on carbon crystals, as indicated by the X-ray diffraction peaks, and the results of the energy-dispersive X-ray spectroscopy confirm the elemental analysis. The carbon-based ink comprises semi-spherical nanoparticles as imaged by the scanning electron microscope. The electrochemical energy storage mechanism of the carbon nanoparticle-based electrode in the sulfuric acid electrolyte depends on the electric double layer, as investigated by the cyclic voltammetry and the galvanostatic charge-discharge measurements. As a result, the carbon ink-based supercapacitor exhibits a maximum areal capacitance of 0.5 mF/cm2 at 0.25 mA/cm2, a maximum energy of 0.2 µWh, and a maximum power of 1600 µW. The electrochemical impedance spectroscopy shows excellent equivalent series resistance of 0.6 ohm, representing a solid attachment of the ink on the stainless steel substrate. In addition, an angle of 45o in the low-frequency range indicates a semi-infinite diffusion of the electrolyte ions into the nanostructured electrodes. All these elemental, morphological, and electrochemical properties of the carbon-based ink promote its potential to be effortlessly implemented as electrodes, thereby contributing to the advancement of supercapacitor manufacture.

Vat photopolymerization 3D printing optimization: Analysis of print conditions and print quality for complex geometries and ocular applications

3D printing, also known as additive manufacturing, continues to reshape manufacturing paradigms in healthcare by providing customized on-demand object fabrication. However, stereolithography-based 3D printers encounter a conflict between optimizing printing parameters, requiring more time, and print efficiency, requiring less time. Moreover, commonly used metrics to assess shape fidelity of 3D printed hydrogel materials like ‘circularity’ and ‘printability’ are limited by the soft nature of hydrogels, that can cause irregularities in their boundary. To unlock the full potential of 3D printing of biomaterials, it is also necessary to understand correlation between printing parameters and ink properties. In this work, a method based on curing depth, overcuring (cumulative cure), and print thickness was developed, which enables a time-efficient and reliable determination of printing conditions for complex geometries using gelatin methacrylate hydrogel biomaterial ink. We also examined the impact of printing direction on the print quality in terms of object/print thickness and aspect ratio. Moreover, the effects of dye concentration, exposure time, and layer thickness on print quality were evaluated, with discussions focused on the correlation between print dimension to layer thickness. Further evaluation was achieved by successfully printing bioinspired corneal stroma-like scaffold and delicate structures like a contact lens and a model eyeball, substantially expanding the scope of this method in producing high-quality prints with intricate details. We also demonstrate the effectiveness of ‘Feret ratio,’ another measure of object shape, in assessing the shape fidelity of different prints. Overall, the results highlight the practical potential of this method in enhancing the speed and reliability of the 3D printing processes involving complex geometries using a low-cost 3D printers.

Effect of Post-Heat Treatment of Catalysts Under Various Gas Conditions on the Microstructure of Catalysts Ink and Electrode for PEMFC

Polymer electrolyte membrane fuel cells (PEMFCs) directly convert the chemical energy of fuel into electrical energy, producing electricity through a high-efficiency, ecofriendly energy conversion device. While PEMFCs are commercialized now, enhancing their competitiveness compared to other energy sources is critical and requires an understanding of the microstructure of the membrane-electrode assembly. Typically, fuel cell electrodes are manufactured by coating an electrolyte membrane with catalyst inks composed of electrode catalyst, ionomer, and solvent or additives. To maximize the performance of fuel cells, the proper distribution of catalysts and ionomers within the electrode is essential, and the microstructure within the electrode is determined by the interactions between the carbon support and platinum surface, as well as the dispersion of catalysts and ionomers in the solvent. Thus, the internal microstructure of the catalyst ink, determined by the interactions among its constituents, ultimately defines the final electrode microstructure, affecting the performance and durability of the fuel cell. This study aims to analyze the effects of post-heat treatment of catalyst in various gas atmospheres, including NH3 gas, on the surface characteristics and to examine the changes in interactions between the catalysts and ionomers within the catalyst ink following surface modification. Additionally, this research seeks to elucidate the correlation between the properties of the catalyst ink and the characteristics of the electrode produced by drying the ink. To this end, the physical properties of the thermally modified catalysts were analyzed, and the resulting catalyst ink was also manufactured and examined. The physical and rheological properties of the catalyst ink were assessed using a dispersing analyzer and rheometer to understand the interactions between the catalysts and ionomers. Furthermore, the coatability of the catalyst ink and the structural characteristics of the electrode were investigated. Figure 1

X-Ray Scattering Characterization of Pt and PtCo Catalyst Inks and Electrodes for PEFC Cathodes

The composition and processing of the catalyst-ionomer ink used to fabricate electrochemical energy conversion device electrodes can impact the final electrode microstructure and performance. Parameters influencing the microstructure and performance are, for example, solvent ratio, ink processing method and time, ionomer chemistry, and carbon morphology/porosity. Polymer electrolyte fuel cell (PEFC) cathodes are typically prepared by first dispersing a catalyst powder, comprised of platinum or platinum alloy nanoparticles supported on carbon blacks, with ionomer in solvents, followed by extensive mixing using a variety of methods. The electrode properties are controlled by the interactions of the ionomer with the catalyst particles and the support in the catalyst-ionomer ink, by the effect of ink solvent composition on those interactions, and by the ink mixing and coating procedures. This presentation will describe the in-situ/ex-situ ultra-small angle X-ray scattering (USAXS) combined with SAXS studies of the evolution of the cathode catalyst layer to determine the effect of ink processing variables and ink composition on the ink properties, especially on the carbon agglomerate break-up for efficient coating of catalyst layers while optimizing fuel cell performance and durability. The effect of ink formulation is examined for Pt-supported Vulcan carbon (Pt/Vu) and Pt and PtCo-supported on high surface area carbon (Pt and PtCo/HSC) with different ionomers. The results provide the fundamental understanding enabling improved membrane-electrode assembly (MEA) performance and durability. Moreover, the results of the evolution of the catalyst layer during the ink drying process as a function of solvent removal rate and solvent identity will be discussed. Acknowledgments This work was supported by the U.S. Department of Energy, Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office under the M2FCT Consortium. This work was authored in Argonne National Laboratory, a U.S. Department of Energy (DOE) Office of Science laboratory operated for DOE by UChicago Argonne, LLC under contract no. DE-AC02-06CH11357. This research used the resources of the Advanced Photon Source (APS), a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357.

Influence of Solvents on Catalyst Layer Performance in Proton Exchange Membrane Water Electrolysis and Fuel Cells

Proton exchange membrane (PEM) water electrolysis (WE) and fuel cells (FCs) stand out as promising technologies for hydrogen generation and utilization, leveraging renewable and sustainable energy sources. A pivotal element in both PEMFC and PEMWE is the membrane-electrode assembly (MEA), comprising catalyst layers (CLs) and a membrane. These CLs facilitate electrochemical reactions at the anode and cathode, crucial for both oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) in PEMWE and PEMFC. The catalyst ink for CLs consists of electrocatalyst, ionomer dispersion, and additional solvents. Among these components, the choice of solvent significantly influences PEMFC and PEMWE performance, shaping the catalyst ink's properties. In this investigation, we formulated ionomer dispersions for CLs to enhance performance in PEMWE and PEMFC. We scrutinized the effects of solvents in terms of solvation energy, thermogravimetric analysis (TGA), particle size distribution (PSD), and electrochemical assessment. Acknowledgments This research was supported in part by the New and Renewable Energy of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) granted financial resource from the Ministry of Trade, Industry & Energy, Republic of Korea (No. 20213030040520) and by 2021 Green Convergence Professional Manpower Training Program of the Korea Environmental Industry and Technology Institute funded by the Ministry of Environment.

Regulating Assembly of Porous Electrode Catalyst Layers

Polymer-electrolyte fuel cells (PEFCs) demonstrate remarkable potential in replacing non-renewable energy resources in paving the way for a sustainable future. PEFCs have fairly high efficiencies and energy densities, making them feasible for applications such as transportation and energy storage. The most expensive units of the PEFCs are the catalyst layers, traditionally composed of platinum interspersed on a carbon support with a perfluorosulfonic acid (PFSA) which stabilizes the ink dispersions as well acts as a binder for the dried catalyst layers. Despite the great importance of optimizing the composition of the catalyst layer to improve the practicality of PEFCs, predicting the performance of the final structure of the fuel cell remains a challenge.In this talk, we outline an approach to predict key properties of the catalyst layers such as the porosity and particle sizes that compose it through mathematical modeling of the ink properties. We discuss a kinetics-based algorithm based on interacting particles that simultaneously solves for the size distributions of the particles and the pH of the ink, a parameter that can be used for verification. The results of the aggregation formulation will be fed into calculations to determine fundamental properties of the catalyst layer, such as porosity through a void fraction calculation. To verify the accuracy of this approach, we will compare against experimental data for varying concentrations and solvents. The insights gained from these considerations will enable efficient design of future catalyst layers.

4D printing of pH-responsive bilayer with programmable shape-shifting behaviour

4D printing of smart materials has seen remarkable advancements in the domain of biomedical devices, with a particular focus on developing responsive and adaptive programmable structures. In this work, we report the 4D printing of two solvent-responsive hydrogels forming a bilayer that undergoes bidirectional actuation depending on the pH of the solvent. A strong interlayer adhesion between the hydrogels is formed without subjecting either of their surfaces to any chemical modification. These hydrogels have an interfacial toughness of 71.8 J/m2 and undergoes no delamination during actuation inside a solvent. Conventionally, pH-responsive actuators are only limited to simple 2D films prepared by solvent casting. However, our work focuses on the design and fabrication of complex bilayer and patterned structures using Direct-Ink Writing (DIW) approach. These printed structures actuate upon immersion in a solvent medium, and the actuation is reversible in nature. The influence of programmable variables on the morphed structure was studied systematically by modifying the rheological properties (in the range of 102−105 Pa.s) and printing parameters (optimized at a printing speed of 5mm/sec, with the extrusion pressure of 5−6 bar and nozzle diameter of 0.5 mm) of the 3D printed bilayer structure. The physicochemical properties of the printable hydrogel ink were tuned such that the same structure can respond to both acidic and basic pH (with non-morphing point at pH 7), by altering the directionality of actuation. We have demonstrated the applications of these pH-responsive actuators in smart valves.

Effect of high-boiling point solvents on inkjet printing of catalyst layers for proton exchange membrane fuel cells

Inkjet printing (IJP) is considered as a promising and flexible method for low cost and drop-on-demand pattern formation in proton exchange membrane (PEM) fuel cells. Although significant advancements have been made in inkjet-printed electrodes, identifying the optimal ink formulations remains challenging due to severe restrictions on the ink properties. Generally, the catalyst layer prepared by IJP using low boiling point solvents (water/alcohol) show reasonable electrochemical performance. However, low boiling point solvents lead to clogging of the printhead nozzle due to fast evaporation of the solvent in the inkjet print head. In this study, high boiling point solvents (propylene glycol (PG) or ethylene glycol (EG)) were used as additives to reduce nozzle clogging and improve printing efficiency. In this context, the relationship between catalyst ink properties, CL microstructure, and electrochemical performance of the MEA is investigated. Results show that printing time is significantly reduced with adding high boiling point solvents in the ink (66.67% reduction of time with 30 wt% PG). However, an increased amount of additive is detrimental in terms of electrochemical performance due to formation of larger agglomerates, lower porosity of the catalyst layer, and reduced ECSA. The results of this work can be used to develop a strategy to adjust the trade-off between printing time and electrochemical performance of electrodes prepared using IJP.

Engineering the Atomic Interface of Refractory‐Metal‐Reinforced Copper Matrix Using Direct Ink 3D Printing

Herein, 3D printing involving metallic materials with substantially distinct melting temperatures and their immiscibility presents a formidable challenge. Nevertheless, it may be possible to overcome this challenge using the direct ink writing (DIW) method within such immiscible systems. In this article, a successful fabrication of Cu‐based composites utilizing the additive manufacturing process that is DIW technique, followed by a post‐sintering process, is presented. The secondary addition to the Cu–matrix includes tantalum (Ta), tungsten (W), and niobium (Nb). The rheological properties of the composite inks are also analyzed for the DIW technique. The underlying reasons behind the increased mechanical, wear, and thermal properties are assessed through experimental and molecular dynamics simulations. Microstructural analysis is conducted using optical and scanning electron microscopes. Mechanical, electrical, thermal, and wear properties are evaluated at ambient temperature, and comparisons are established with DIW‐processed pure Cu. Elemental mapping through energy‐dispersive spectroscopy and high‐resolution transmission electron microscopy confirm the distribution of W, Ta, and Nb particles within the composite. The 3D printing of immiscible alloy components opens new avenues for exploring novel material properties, mixtures, and composite materials, thus fostering the development of innovative materials.

Polymer microsphere inks for semi-solid extrusion 3D printing at ambient conditions

Extrusion-based 3D printing methods have great potential for manufacturing of personalized polymer-based drug-releasing systems. However, traditional melt-based extrusion techniques are often unsuitable for processing thermally labile molecules. Consequently, methods that utilize the extrusion of semi-solid inks under mild conditions are frequently employed. The rheological properties of the semi-solid inks have a substantial impact on the 3D printability, making it necessary to evaluate and tailor these properties. Here, we report a novel semi-solid extrusion 3D printing method based on utilization of a Carbopol gel matrix containing various concentrations of polymeric microspheres. We also demonstrate the use of a solvent vapor-based post-processing method for enhancing the mechanical strength of the printed objects. As our approach enables room-temperature processing of polymers typically used in the pharmaceutical industry, it may also facilitate the broader application of 3D printing and microsphere technologies in preparation of personalized medicine.

Research on the performance of high-strength explosive ink and application of direct writing technology in micro-explosive network

With the widespread application of 3D direct writing technology in the field of energetic materials, it has become a current research topic to design an explosive ink with excellent micro-size detonation performance and high-strength mechanical properties and combining it with explosion network technology to improve detonation synchronization has become a research hotspot. This article uses FEVE-F2311 and PF as the composite bonding system, submicron CL-20 as the main explosive, and adds an appropriate amount of TDI as the curing agent to prepare an explosive ink with excellent micro-size detonation performance and high-strength mechanical properties. Research shows that the explosive ink has a detonation velocity of 7322 m·s−1 at a charge density of 1.621 g·cm−3, a critical propagation size of 0.3×0.3 mm, a critical propagation thickness of 1×0.040 mm, and a maximum detonation Corners can reach 160°. The error of detonation synchronization in the "one in and six out" micro-explosion network is within 150 ns, showing excellent detonation synchronization. The nano-indentation test shows that the average elastic modulus of CL-20-based explosive ink is 6.991 GPa and the average hardness is 0.200 GPa, showing excellent mechanical properties; the compressive stress-strain curve shows that its average compressive stress is 7.62 MPa, showing excellent Compressive strength. It not only greatly improves the mechanical properties of explosive ink, but also provides a method to improve the synchronization performance of micro-explosive networks.

High-precision silver electrode based on PEN substrate with robust mechanical performance

Wearable electronics are becoming more and more popular, and in order to ensure the safety and accuracy of wearable electronics, the requirements for the refinement and stability of flexible electrodes are getting higher and higher. The reduction of the amount of ink jet and the reduction of surface charge density and electrostatic stress near the nozzle hole can significantly improve the jetting state of the ink. And nozzle voltage is a key factor that affects them. The spreading of ink droplets on the substrate and the formation of a specific pattern is a dynamic process, which is closely related to the properties of the substrate and the state of the ink droplets. In this paper, PEN is used as the substrate to print silver electrode, with its good thermal stability and good mechanical properties. In order to solve these problems and improve the accuracy of the electrode pattern on PEN substrate, a joint control method of ink drop spacing and nozzle voltage is proposed. It is found that the accuracy of the pattern increases with the increase of the drop spacing. At 45 μm, 90.91 % of the pattern accuracy with the ideal pattern can be achieved. As the nozzle voltage decreases, so does the satellite spot. And at 25 V, it can achieve satellite-free spot printing. Because this method avoids the adjustment of ink properties and the regulation of voltage waveform, this advancement provides a simpler solution for patterned high-precision printed silver electrodes based on flexible substrates. In addition, a silver electrode with a resistivity of 3.43 μΩ·cm was obtained at an annealing temperature of 160 °C. The resistivity change of the electrode only 7.58 % under 5000 times of bending. This is very rare in flexible electrodes.The silver film on the PEN substrate exhibited excellent adhesion under the tape test. XPS depth profiling was used to characterize the elemental states of the films at different depths. The results indicated that the coordination bond between the PEN substrate and the Ag film resulted in good bending resistance, which gives a persuasive explanation for the first time. This result is also due to the precise handling of the film, which also results in a homogeneous distribution of the film. It solves the problem of poor adhesion of silver electrodes based on other substrates or other preparation methods. Therefore, silver electrodes based on PEN substrates have a broad application prospect in the field of flexible wearable electronics.

Revolutionizing Intervertebral Disc Regeneration: Advances and Future Directions in Three-Dimensional Bioprinting of Hydrogel Scaffolds.

Hydrogels are multifunctional platforms. Through reasonable structure and function design, they use material engineering to adjust their physical and chemical properties, such as pore size, microstructure, degradability, stimulus-response characteristics, etc. and have a variety of biomedical applications. Hydrogel three-dimensional (3D) printing has emerged as a promising technique for the precise deposition of cell-laden biomaterials, enabling the fabrication of intricate 3D structures such as artificial vertebrae and intervertebral discs (IVDs). Despite being in the early stages, 3D printing techniques have shown great potential in the field of regenerative medicine for the fabrication of various transplantable tissues within the human body. Currently, the utilization of engineered hydrogels as carriers or scaffolds for treating intervertebral disc degeneration (IVDD) presents numerous challenges. However, it remains an indispensable multifunctional manufacturing technology that is imperative in addressing the escalating issue of IVDD. Moreover, it holds the potential to serve as a micron-scale platform for a diverse range of applications. This review primarily concentrates on emerging treatment strategies for IVDD, providing an in-depth analysis of their merits and drawbacks, as well as the challenges that need to be addressed. Furthermore, it extensively explores the biological properties of hydrogels and various nanoscale biomaterial inks, compares different prevalent manufacturing processes utilized in 3D printing, and thoroughly examines the potential clinical applications and prospects of integrating 3D printing technology with hydrogels.