Printing Ink Research Articles

Electrochemical Diffusion Study in Poly(Ethylene Glycol) Dimethacrylate-Based Hydrogels.

Hydrogels are of great importance for functionalizing sensors and microfluidics, and poly(ethylene glycol) dimethacrylate (PEG-DMA) is often used as a viscosifier for printable hydrogel precursor inks. In this study, 1-10 kDa PEG-DMA based hydrogels were characterized by gravimetric and electrochemical methods to investigate the diffusivity of small molecules and proteins. Swelling ratios (SRs) of 14.43-9.24, as well as mesh sizes ξ of 3.58-6.91 nm were calculated, and it was found that the SR correlates with the molar concentration of PEG-DMA in the ink (MCI) (SR = 0.1127 × MCI + 8.3256, R2 = 0.9692) and ξ correlates with the molecular weight (Mw) (ξ = 0.3382 × Mw + 3.638, R2 = 0.9451). To investigate the sensing properties, methylene blue (MB) and MB-conjugated proteins were measured on electrochemical sensors with and without hydrogel coating. It was found that on sensors with 10 kDa PEG-DMA hydrogel modification, the DPV peak currents were reduced to 92 % for MB, 73 % for MB-BSA, and 23 % for MB-IgG. To investigate the diffusion properties of MB(-conjugates) in hydrogels with 1-10 kDa PEG-DMA, diffusivity was calculated from the current equation. It was found that diffusivity increases with increasing ξ. Finally, the release of MB-BSA was detected after drying the MB-BSA-containing hydrogel, which is a promising result for the development of hydrogel-based reagent reservoirs for biosensing.

High internal phase emulsions gel ink for direct-ink-writing 3D printing of liquid metal

3D printing of liquid metal remains a big challenge due to its low viscosity and large surface tension. In this study, we use Carbopol hydrogel and liquid gallium-indium alloy to prepare a liquid metal high internal phase emulsion gel ink, which can be used for direct-ink-writing 3D printing. The high volume fraction (up to 82.5%) of the liquid metal dispersed phase gives the ink excellent elastic properties, while the Carbopol hydrogel, as the continuous phase, provides lubrication for the liquid metal droplets, ensuring smooth flow of the ink during shear extrusion. These enable high-resolution and shape-stable 3D printing of three-dimensional structures. Moreover, the liquid metal droplets exhibit an electrocapillary phenomenon in the Carbopol hydrogel, which allows for demulsification by an electric field and enables electrical connectivity between droplets. We have also achieved the printing of ink on flexible, non-planar structures, and demonstrated the potential for alternating printing with various materials.

Towards Expanding the Use of Paper Made from Recycled and Non-Woody Plants: Enhancing the Print Quality through the Application of Nano-Modified Offset Inks

This study aims to investigate the feasibility of using paper made from eco-friendly recycled and non-woody plants in graphic technology, particularly in offset printing. Instead of changing the composition or modifying the surface properties of the paper, the focus was on enhancing the print quality by modifying the printing ink. By modifying the printing inks, the quality of the prints on recycled and non-woody paper can be optimized, which in turn reduces the need for paper made from primary fibers. This approach can expand the use of alternative materials in graphic technology and design. The objective was to optimize the print quality on these sustainable materials. Five types of uncoated paper were used, with high-quality uncoated offset paper based on virgin fibers serving as a reference. Laboratory tests of the basic and surface properties were carried out to measure the paper quality parameters that are important for offset printing. The influence of the paper composition on its optical and colorimetric properties was also investigated. The interaction between the selected papers and offset inks was examined through measurements of adhesion parameters and ink transfer, i.e., the paper’s ability to accept the ink. To enhance the applicability of the investigated papers as printing substrates in the graphic industry, SiO2 and TiO2 nanoparticles were added to the offset inks. The influence of the paper composition on the colorimetric properties of the prints was also investigated. The print uniformity, as an important quality characteristic, was determined by measuring the mottling index. The research findings indicate that incorporating SiO2 and TiO2 nanoparticles into offset inks can enhance the interaction between the paper and ink, leading to improved print quality. This study provides new perspectives on the possibilities of using recycled and non-woody plant paper in offset printing without significantly compromising the quality of the print.

Alternative Metallic Fillers for the Preparation of Conductive Nanoinks for Sustainable Electronics

AbstractThe development of electronics with net zero carbon emissions through more efficient and environmentally friendly materials and processes is still a challenge. Here, alternative chemical synthesis routes of metal conductive nanoparticles, based on biodegradable materials are explored, such as nickel, iron–nickel alloy and iron nanoparticles, to be used, in the long term, as fillers in inks for inject printing. Thus, Ni and FeNi metal nanoparticles of 25–12 nm, forming aggregates of 614–574 nm, respectively, are synthesized in water in the presence of a polyol and a reducing agent and under microwave heating that enables a more uniform and fast heating. Iron nanoparticles of 120 ± 40 nm are synthesized in polyol that limits the aggregation and the oxidation degree. Commercial metal nanoparticles of iron and nickel, are coated with ethylene glycol and used for comparison. The conductivity of nanoparticles when pressed into pellets remains similar for both commercial and synthesized samples. However, when deposited on a strip line and heated, synthesized Ni, FeNi, and Fe nanoparticles show significant conductivity and interesting magnetic properties. It is demonstrated that the nanosize facilitates sintering at reduced temperatures and the capping agents prevent oxidation, resulting in promising conductive fillers for printed electronic applications.

Applications of physical and chemical treatments in plant-based gels for food 3D printing.

Extrusion-based three-dimensional (3D) printing has been extensively studied in the food manufacturing industry. This technology places particular emphasis on the rheological properties of the printing ink. Gel system is the most suitable ink system and benefits from the composition of plant raw materials and gel properties of multiple components; green, healthy aspects of the advantages of the development of plant-based gel system has achieved a great deal of attention. However, the relevant treatment technologies are still only at the laboratory stage. With a view toward encouraging further optimization of ink printing performance and advances in this field, in this review, we present a comprehensive overview of the application of diverse plant-based gel systems in 3D food printing and emphasize the utilization of different treatment methods to enhance the printability of these gel systems. The treatment technologies described in this review are categorized into three distinct groups, physical, chemical, and physicochemical synergistic treatments. We comprehensively assess the specific application of these technologies in various plant-based gel 3D printing systems and present valuable insights regarding the challenges and opportunities for further advances in this field.

20‐2: High‐resolution Pixelated Quantum Dot Light Emitting Diodes via Electrohydrodynamic Printing Technology

In this study, we achieved high‐resolution pixelated QLED device with 500 pixels per inch (ppi) through electrohydrodynamic printing (EHD) technology. We optimize the EHD printing process by controlling ink viscosity and printing speed to obtain a uniform and flat emission layer film. Then, we prepared high‐resolution pixelated bottom‐emission and top‐emission PMQLED with maximum current efficiencies of 13.6 cd/A and 16.4 cd/A, respectively. Finally, we fabricated a 500 ppi red and green (R/G) dual‐color bottom‐emission QLED device using the EHD printing method. The successful preparation of these 500 ppi QLED devices with high efficiency indicated that the EHD printing method can provides a technical basis for developing the high‐resolution QLED display technology in the future.

High-resolution 3D printable inks based on functional polymeric ionic liquids for applications in carbon dioxide valorization

This study investigates the use of epoxy-functionalized acrylate-based 3D printable ink for creating high-resolution functionalized devices, exploring the possibility to further functionalize those for chemical engineering applications. In fact, the control of the epoxy-functionalized surface enables the formation of active surfaces, and this study employs supported Ionic Liquids with catalytic properties as a proof of concept. Ionic liquids (ILs) and polymeric derivatives represent a promising path to generate multifunctional complex 3D structures, playing advanced roles in multiple applications. The fine-tuning of the functionalization methodology and formulation enhances the resolution of acrylate-based resins, allowing the production of highly detailed structures that can significantly boost catalytic efficiency. Through a comparison with commercial resins, the developed formulation demonstrates superior resolution capabilities, positioning it as an effective alternative for use in vat photopolymerization technologies. Additionally, controlling the level of functionalization and accessibility of the ILs' active sites through the control of the surface area of the reactor has led to improved process performance in terms of yield and space-time yield (STY) in the CO2 cycloaddition to epoxide reaction.

Recent advances in photoresponsive printing inks for security encoding applications

AbstractCounterfeiting of banknotes, important documents, and branded goods continues to be a major worldwide problem for governments, businesses, and consumers. This problem has serious financial, security, and health implications. Due to their stability for printing on various substrates, the photochromic anticounterfeiting inks have received important interest. There have been various photochromic agents, such as polymer nanoparticles, quantum and carbon dots, and organic and inorganic fluorophores and luminophores, which have been broadly used for antiforging applications. In comparison to organic agents, inorganic photochromic materials have better stability under reversible/long‐term light illumination. Recently, the remarkable optical characteristics and chemical stability of photoluminescent and photochromic agents have led to their extensive usage anticounterfeiting products. There have been also several strategies to tackle the rising problem of counterfeiting. Both of solvent‐based and water‐based inks have been developed for security encoding purposes. Additionally, the printing methods, including screen printing, labeling, stamping, inkjet printing, and handwriting, that have been used to apply anticounterfeiting inks onto various surfaces are discussed. The limitations of photoluminescent and photochromic agents and the potential for their future preparation to combat counterfeiting were discussed. This review would benefit academic researchers and industrial developers who are interested in the area of security printing.

Programmable multimode optical encryption of advanced printable security inks by integrating structural color with Down/Up- conversion photoluminescence

Optical information encryption with high encoding capacities can significantly boost the security level of anti-counterfeiting in the scenario of guaranteeing the authenticity of a wide scope of common and luxury goods. In this work, a novel counterfeiting material with high-degree complexity is fabricated by microencapsulating cholesteric liquid crystals and triplet–triplet annihilation upconversion fluorophores to integrate structural coloration with fluorescence and upconversion photoluminescence. Moreover, the multimode security ink presents tailorable optical behaviors and programmable abilities on flexible substrates by various printing techniques, which offers distinct information encryption under different optical modes. The advanced strategy provides a practical versatile platform for high-secure-level multimode optical inks with largely enhanced encoding capacities, programmability, printability, and cost-effectiveness, which manifests enormous potentials for information encryption and anti-counterfeiting technology.

Carbon nanotube as a conductive rheological modifier for carbon fiber-reinforced epoxy 3D printing inks

Rheological modifiers enable direct ink writing of polymers with low viscosity such as epoxy without requiring light or heat. Modifiers that conduct electrons and phonons impart multifunctional properties to 3D printed polymers. Here, we report the development of printable nanocomposite inks comprised of epoxy, carbon fibers (CFs), and carbon nanotubes (CNTs) to achieve excellent mechanical properties and multifunctionality via high electrical conductivity required for next-generation light weight aerospace, electronics, and energy applications. CF and CNT concentrations of 8.5 and 1.7 wt%, respectively, render the material shear-thinning with a high yield stress, hence printable and self-supporting after being printed. An average electrical conductivity of 10−2 S/cm and thermal conductivity of 0.3 W/m.K were measured for the 3D-printed multi-layer structures. Furthermore, tensile modulus, tensile strength, flexural modulus, and flexural strength were measured to be 5.8, 0.08, 6.0, and 0.1 GPa, respectively. Compared with other 3D printed conductive polymer nanocomposites with reported electrical conductivity and elastic modulus, the structures here have the highest specific elastic modulus. They also possess the highest electrical conductivity among the 3D printed polymeric composites of carbon nanomaterials with an elastic modulus above 1 GPa. This is due to the outstanding combination of CNTs, CFs, and epoxy. The results expand the range of polymer properties for multifunctional applications.

Wearable, battery-free, wireless multiplexed printed sensors for heat stroke prevention with mussel-inspired bio-adhesive membranes

Wearable technologies are becoming pervasive in our society, and their development continues to accelerate the untapped potential of continuous and ubiquitous sensing, coupled with big data analysis and interpretation, has only just begun to unfold. However, existing wearable devices are still bulky (mainly due to batteries and electronics) and have suboptimal skin contact. In this work, we propose a novel approach based on a sensor network produced through inkjet printing of nanofunctional inks onto a semipermeable substrate. This network enables real-time monitoring of critical physiological parameters, including temperature, humidity, and muscle contraction. Remarkably, our system operates under battery-free and wireless near-field communication (NFC) technology for data readout via smartphones. Moreover, two of the three sensors were integrated onto a naturally adhesive bioinspired membrane. This membrane, developed using an eco-friendly, high-throughput process, draws inspiration from the remarkable adhesive properties of mussel-inspired molecules. The resulting ultra-conformable membrane adheres effortlessly to the skin, ensuring reliable and continuous data collection. The urgency of effective monitoring systems cannot be overstated, especially in the context of rising heat stroke incidents attributed to climate change and high-risk occupations. Heat stroke manifests as elevated skin temperature, lack of sweating, and seizures. Swift intervention is crucial to prevent progression to coma or fatality. Therefore, our proposed system holds immense promise for the monitoring of these parameters on the field, benefiting both the general population and high-risk workers, such as firefighters.

Development of novel 3D printable inks for protein delivery

The application of 3D printing technology in the delivery of macromolecules, such as proteins and enzymes, is limited by the lack of suitable inks. In this study, we report the development of novel inks for 3D printing of constructs containing proteins while maintaining the activity of the proteins during and after printing. Different ink formulations containing Pluronic F-127 (20–35 %, w/v), trehalose (2–10 %, w/v) or mannitol, poly (ethylene glycol) diacrylate (PEGDA) (0 or 10 %, w/w), and diphenyl(2,4,6-trimethylbenzoyl) phosphine oxide (TPO, 0 or 0.2 mg/mL) were prepared for 3D-microextrusion printing. The F2 formulation that contained β-galactosidase (β-gal) as a model enzyme, Pluronic F-127 (30 %), and trehalose (10 %) demonstrated the desired viscosity, printability, and dose flexibility. The shear-thinning property of the F2 formulation enabled the printing of β-gal containing constructs with a good peak force during extrusion. After 3D printing, the enzymatic activity of the β-gal in the constructs was maintained for an extended period, depending on the construct design and storage conditions. For instance, there was a 50 % reduction in β-gal activity in the two-layer constructs, but only a 20 % reduction in the four-layer construct (i.e., 54.5 ± 1.2 % and 82.7 ± 9.9 %, respectively), after 4 days of storage. The β-gal activity in constructs printed from the F2 formulation was maintained for up to 20 days when stored in sealed bags at room temperatures (21 ± 2 °C), but not when stored unsealed in the same conditions (e.g., ∼60 % activity loss within 7 days). The β-gal from constructs printed from F2 started to release within 5 min and reached 100 % after 20 min. With the design flexibility offered by the 3D printing, the β-gal release from the constructs was delayed to 3 h by printing a backing layer of β-gal-free F5 ink on the constructs printed from the F2 ink. Finally, ovalbumin as an alternative protein was also incorporated in similar ink compositions. Ovalbumin exhibited a release profile like that of the β-gal, and the release can also be modified with different shape design and/or ink composition. In conclusion, ink formulations that possess desirable properties for 3D printing of protein-containing constructs while maintaining the protein activity during and after printing were developed.

Effect of Sodium Phosphate and Cellulose Ethers on MgO/SiO2 Cements for the 3D Printing of Forsterite Bioceramics

Magnesium silicate ceramics are promising materials for bone tissue regeneration and can be prepared through 3D printing of magnesium oxide/silica (MgO/SiO2) cement pastes followed by calcination. Despite the growing interest in these formulations, additive manufacturing technology has only recently been explored for these cements, and the effects of admixtures and additives on such printing inks remain largely unexplored. In this study, we prepared various MgO/SiO2 cement formulations with differing amounts of sodium orthophosphate, a setting retarder, and cellulose ethers, used as rheo-modifiers. The samples’ setting properties were investigated, and printing parameters were properly adjusted. The most promising formulations were then 3D printed and calcined to obtain forsterite bioceramics, which were further characterized using confocal Raman microscopy, scanning electron microscopy, atomic force microscopy, gas porosimetry, and compressive strength tests. Our results revealed that the cellulose derivatives influence the printability of the MgO/SiO2 formulations without affecting the hardening time, which can be adjusted by the addition of sodium phosphate. The use of fine-tuned formulations allowed for the preparation of 3D-printed forsterite bioceramics, potentially suitable for biological applications as cancellous bone scaffolds.

Rheology of plant protein–polysaccharide gel inks for 3D food printing: Modeling and structure–property relations

Plant protein–polysaccharide composite hydrogels and emulsion gels are attractive materials for production of edible inks for 3D food printing. Their ability to satisfy the printability requirements is conventionally evaluated in small- and large-amplitude oscillatory shear tests. A model is derived that describes experimental data in linear and nonlinear rheological tests on protein gels in a unified manner. The model is based on the population-balance approach and involves a reasonably small number of adjustable parameters. Fitting observations on soy protein isolate–xanthan gum, peanut protein–gellan gum, peanut protein–carrageenan, pea protein–carrageenan and pea protein isolate–flaxseed gum gels demonstrates that material parameters evolve consistently with composition of the gels. The governing equations describe adequately the effects of pH and ionic strength of aqueous solutions on the mechanical properties of the gels and predict the stress–strain Lissajous curves and the crossover amplitudes for transition from the solid-like to fluid-like response. Based on the analysis of observations in large-amplitude oscillatory tests with various frequencies, a mechanism is proposed for transition from the type-I (strain thinning) to type-III (weak strain overshoot) response of protein–polysaccharide gels.

Influence of Surface Chemical and Topographical Properties on Morphology, Wettability and Surface Coverage of Inkjet-Printed Graphene-Based Materials.

The inkjet printing of water-based graphene and graphene oxide inks on five substrates, two rigid (silicon and glass) and three flexible (cellulose, indium tin oxide-coated polyethylene terephthalate (ITO-PET) and ceramic coated paper (PEL paper)), is reported in this work. The physical properties of the inks, the chemical/topographical properties of selected substrates, and the inkjet printing (IJP) of the graphene-based materials, including the optimisation of the printing parameters together with the morphological characterisation of the printed layers, are investigated and described in this article. Furthermore, the impact of both the chemical and topographical properties of the substrates and the physical properties of graphene-based inks on the morphology, wettability and surface coverage of the inkjet-printed graphene patterns is studied and discussed in detail.

All Screen Printed and Flexible Silicon Carbide NTC Thermistors for Temperature Sensing Applications.

In this study, Silicon Carbide (SiC) nanoparticle-based serigraphic printing inks were formulated to fabricate highly sensitive and wide temperature range printed thermistors. Inter-digitated electrodes (IDEs) were screen printed onto Kapton® substrate using commercially avaiable silver ink. Thermistor inks with different weight ratios of SiC nanoparticles were printed atop the IDE structures to form fully printed thermistors. The thermistors were tested over a wide temperature range form 25 °C to 170 °C, exhibiting excellent repeatability and stability over 15 h of continuous operation. Optimal device performance was achieved with 30 wt.% SiC-polyimide ink. We report highly sensitive devices with a TCR of -0.556%/°C, a thermal coefficient of 502 K (β-index) and an activation energy of 0.08 eV. Further, the thermistor demonstrates an accuracy of ±1.35 °C, which is well within the range offered by commercially available high sensitivity thermistors. SiC thermistors exhibit a small 6.5% drift due to changes in relative humidity between 10 and 90%RH and a 4.2% drift in baseline resistance after 100 cycles of aggressive bend testing at a 40° angle. The use of commercially available low-cost materials, simplicity of design and fabrication techniques coupled with the chemical inertness of the Kapton® substrate and SiC nanoparticles paves the way to use all-printed SiC thermistors towards a wide range of applications where temperature monitoring is vital for optimal system performance.

A comprehensive bench-to-bed look into the application of gamma-sterilized 3D-printed polycaprolactone/hydroxyapatite implants for craniomaxillofacial defects, an in vitro, in vivo, and clinical study

This study investigates the safety and efficacy of 3D-printed polycaprolactone/hydroxyapatite (PCL/HA) scaffolds for patient-specific cranioplasty surgeries, employing liquid deposition modeling (LDM) technology. This research is pioneering as it explores the impact of gamma radiation on PCL/HA scaffolds and utilizes printing ink with the highest content of HA known in the composite. The mechanical, morphological, and macromolecular stability of the gamma-sterilized scaffolds were verified before implantation. Subsequent research involving animal subjects was conducted to explore the effects of sterilized implants. Eventually, three clinical cases were selected for the implantation studies as part of a phase 1 non-randomized open-label clinical trial. It was shown that a 25 kGy gamma-ray dose for sterilizing the printed implants did not alter the required geometrical precision of the printed implants. The implants exhibited well-distributed HA and strength comparable to cancellous bone. Gamma radiation reduced hydrophobicity and water uptake capacity without inducing pyrogenic or inflammatory responses. Personalized PCL/HA substitutes successfully treated various craniomaxillofacial defects, including trauma-induced facial asymmetry and congenital deformities. HA nanoparticles in the ink stimulated significant osteoconductive responses within three months of implantation. Moreover, the results revealed that while larger implants may exhibit a slower bone formation response in comparison to smaller implants, they generally had an acceptable rate and volume of bone formation. This clinical trial suggests the application of a sterilized PCL/HA composite for craniomaxillofacial surgery is safe and could be considered as a substitute for autologous bone.

Printable MXene Ink Hybridized with ZSM-5 for Gas Sensing and CO2 Capturing

MXene has garnered significant attention as a two-dimensional material with exceptional physicochemical properties for gas sensing development. This study utilized ZSM-5 nanoparticles loaded with MXene to prepare printable inks, aiming to explore novel applications of MXene in the gas sensing field. The morphology of MXene/ZSM-5 was characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM), demonstrating the typical layered structure of MXene and particle morphology of composite ZSM-5. X-ray photoelectron spectroscopy (XPS) confirmed no production of TiO2 by providing valence information on elements. Thermogravimetric analysis (TG) revealed excellent thermal stability. To verify functional gas sensing feasibility, various hydrocarbons and common gases underwent adsorption and desorption tests (BET). Results showed that MXene loaded with ZSM-5 exhibited good adsorbability for C4H10, C7H8, SF6, H2O and O2 while having a certain trapping effect on CO2. Through testing and analyzing printing results, it was found that the MXene/ZSM-5 ink overcame dispersion issues present in pure MXene ink.

A Novel Strategy for Fabrication of Polyamide 66/Nanohydroxyapatite Composite Bone Repair Scaffolds by Low-Temperature Three-Dimensional Printing.

Due to the decomposition temperature of Polyamide 66 (PA66) in the environment is close to its thermoforming temperature, it is difficult to construct porous scaffolds of PA66/nanohydroxyapatite (PA66/HAp) by fused deposition modeling (FDM) three-dimensional (3D) printing. In this study, we demonstrated for the first time a method for 3D printing PA66/HAp composites at room temperature, prepared PA66/HAp printing ink using a mixed solvent of formic acid/dichloromethane (FA/DCM), and constructed a series of composite scaffolds with varying HAp content. This printing system can print composite materials with a high HAp content of 60 wt %, which is close to the mineral content in natural bone. The physicochemical evaluation presented that the hydroxyapatite was uniformly distributed within the PA66 matrix, and the PA66/HAp composite scaffold with 30 wt % HAp content exhibited optimal mechanical properties and printability. The results of in vitro cell culture experiments indicated that the incorporation of HAp into the PA66 matrix significantly improved the cell adhesion, proliferation, and osteogenic differentiation of bone marrow stromal cells (BMSCs) cultured on the scaffold. In vivo animal experiments suggested that the PA66/HAp composite material with 30 wt % HAp content had the best structural maintenance and osteogenic performance. The three-dimensional PA66/HAp composite scaffold prepared by low temperature printing in the current study holds great potential for the repair of large-area bone defects.

One-Pot Synthesis of Functionalised rGO/AgNPs Hybrids as Pigments for Highly Conductive Printing Inks.

This work provides a method for the development of conductive water-based printing inks for gravure, flexography and screen-printing incorporating commercial resins that are already used in the printing industry. The development of the respective conductive materials/pigments is based on the simultaneous (in one step) reduction of silver salts and graphene oxide in the presence of 2,5-diaminobenzenesulfonic acid that is used for the first time as the common in-situ reducing agent for these two reactions. The presence of aminophenylsulfonic derivatives is essential for the reduction procedure and in parallel leads to the enrichment of the graphene surface with aminophenylsulfonic groups that provide a high hydrophilicity to the final materials/pigments.