Ink Materials Research Articles

Solution-Processable and Printable Two-Dimensional Transition Metal Dichalcogenide Inks.

Two-dimensional (2D) transition metal dichalcogenides (TMDs) with layered crystal structures have been attracting enormous research interest for their atomic thickness, mechanical flexibility, and excellent electronic/optoelectronic properties for applications in diverse technological areas. Solution-processable 2D TMD inks are promising for large-scale production of functional thin films at an affordable cost, using high-throughput solution-based processing techniques such as printing and roll-to-roll fabrications. This paper provides a comprehensive review of the chemical synthesis of solution-processable and printable 2D TMD ink materials and the subsequent assembly into thin films for diverse applications. We start with the chemical principles and protocols of various synthesis methods for 2D TMD nanosheet crystals in the solution phase. The solution-based techniques for depositing ink materials into solid-state thin films are discussed. Then, we review the applications of these solution-processable thin films in diverse technological areas including electronics, optoelectronics, and others. To conclude, a summary of the key scientific/technical challenges and future research opportunities of solution-processable TMD inks is provided.

Low-Concentration Gelatin Methacryloyl Hydrogel with Tunable 3D Extrusion Printability and Cytocompatibility: Exploring Quantitative Process Science and Biophysical Properties.

Three-dimensional (3D) bioprinting of hydrogels with a wide spectrum of compositions has been widely investigated. Despite such efforts, a comprehensive understanding of the correlation among the process science, buildability, and biophysical properties of the hydrogels for a targeted clinical application has not been developed in the scientific community. In particular, the quantitative analysis across the entire developmental path for 3D extrusion bioprinting of such scaffolds is not widely reported. In the present work, we addressed this gap by using widely investigated biomaterials, such as gelatin methacryloyl (GelMA), as a model system. Using extensive experiments and quantitative analysis, we analyzed how the individual components of methacrylated carboxymethyl cellulose (mCMC), needle-shaped nanohydroxyapatite (nHAp), and poly(ethylene glycol)diacrylate (PEGDA) with GelMA as baseline matrix of the multifunctional bioink can influence the biophysical properties, printability, and cellular functionality. The complex interplay among the biomaterial ink formulations, viscoelastic properties, and printability toward the large structure buildability (structurally stable cube scaffolds with 15 mm edge) has been explored. Intriguingly, the incorporation of PEGDA into the GelMA/mCMC matrix offered improved compressive modulus (∼40-fold), reduced swelling ratio (∼2-fold), and degradation rates (∼30-fold) compared to pristine GelMA. The correlation among microstructural pore architecture, biophysical properties, and cytocompatibility is also established for the biomaterial inks. These photopolymerizable bio(material)inks served as the platform for the growth and development of bone and cartilage matrix when human mesenchymal stem cells (hMSCs) are either seeded on two-dimensional (2D) substrates or encapsulated on 3D scaffolds. Taken together, this present study unequivocally establishes a significant step forward in the development of a broad spectrum of shape-fidelity compliant bioink for the 3D bioprinting of multifunctional scaffolds and emphasizes the need for invoking more quantitative analysis in establishing process-microstructure-property correlation.

Material extrusion 3D printing of ceramic structures with overhangs: rheological aspect and introduction of powder-on-demand supporter

Additive manufacturing (AM), represented as a manufacturing process, which is easily applicable to intricate designs, is widely considered in a variety of industries as a simple and cost-effective solution that complements or replaces traditional manufacturing processes. However, due to the demanding properties of ink materials employing ceramic materials, more stringent considerations are required in selecting an appropriate printing technique and implementing the rheological properties of the ceramic ink suitable for the selected printing technique. Here, material extrusion (ME) was selected as a 3D technique applicable to ceramic materials, and the rheological requirements of ceramic pastes that maximize their printability in ME were scrutinized in detail. It was found that the viscoelastic properties of the ceramic pastes played an important role in determining the flowability, cumulative height, and overhang angles that can be allowed in ME. A new supporter system for overhangs, powder-on-demand supporter (PODS), was introduced to ME and demonstrated to understand if PODS can further extend the limits in cumulative height and overhang angles allowed in ME.

3D vat photopolymerization printing of hydrophilic silicone-based microfluidic devices and the effect of cellulose nanocrystals as additives for improved printing accuracy

The lack of an ideal silicone-based ink material with optimal printability has significantly limited the potential to fabricate silicone-based microfluidic devices via 3D vat photopolymerization (VPP) printing. Oftentimes, photoabsorbers are incorporated into the ink material for better control of the photocuring depth in order to avoid excessive curing of unwanted parts. However, the search for a suitable photoabsorber without staining the ink material remains challenging due to the need to retain the clear interface in the final printed product. Herein, we present the fabrication of highly precise and transparent microfluidic devices using hydrophilic silicone-based ink via 3D VPP printing upon photocuring depth adjustment with cellulose nanocrystals (CNC). With the optimal CNC content, the ink material demonstrates enhanced printing accuracy with highly precise replication of channel patterns consisting of near zero deviation in width dimension down to 100 µm. Moreover, the addition of optimal CNC content exhibits no distinct final color and has no negative impact on the pre-gel viscosity and the gel point of the developed ink material. Moving on, the printed devices exhibit excellent fluid manipulation with various solvents for up to 24 hours, with incubation temperature up to 100ºC for 5 hours, and with a continuous flow rate up to 20 mL/min. The sustainable hydrophilicity, good organic solvent resistance, and excellent biocompatibility properties of the printed material further eliminate the need for additional surface modification to suit its application with either organic solvents or biological cells. To the best of our knowledge, the approach to tuning the photocuring depth of ink material with CNC is not widely reported. Besides, the successful fabrication of a highly detailed, neutral-colored, and highly functional hydrophilic silicone-based microfluidic device via 3D VPP printing upon the incorporation of CNC introduces a new avenue in terms of printing material and fabrication method for the mass production of microfluidic devices.

On the cogent formulation of an elastomeric silicone ink material for direct ink write (DIW) 3D printing

AbstractAdhesives and sealants show fine rheology with good physical and mechanical properties as viscous pastes, a possible starting point for developing direct ink writing (DIW) 3D printing ink. However, many commercial adhesives and sealants take days or weeks to cure fully. DIW 3D‐printed parts made directly from these sealants are not designed for a scalable manufacturing process and high‐volume production. Moreover, most of these adhesives and sealants have volume shrinkage during cure. A systematic understanding of formulation methods and design principles for an elastomeric silicone DIW ink can overcome these issues. This study presents the cogent formulation development of a 3D printable thermoset elastomer silicone that gels and cures isotropically in minutes, reducing cycle time for rapid ink development with no shrinkage during cure. More specifically, we outline the principles of raw material selection of a formulation to achieve excellent rheology, printability, synchronized working, and gel time fitting requirements closer to scalable manufacturing. The reaction kinetics and their corresponding 3D‐printed structural properties are also described. Interest in future work is toward a rational DIW 3D printing ink material development protocol and use of machine learning (ML).Highlights Formulation method flexibility and design principle of DIW ink. Raw material selection principle to achieve optimal rheology for DIW printing. Ink gel kinetics for large‐scale DIW manufacturing. Hydrosilylation conversion over time at different ambient temperatures. Structural properties of DIW 3D printed parts.

Gelatin Methacryloyl (GelMA)-Based Biomaterial Inks: Process Science for 3D/4D Printing and Current Status.

Tissue engineering for injured tissue replacement and regeneration has been a subject of investigation over the last 30 years, and there has been considerable interest in using additive manufacturing to achieve these goals. Despite such efforts, many key questions remain unanswered, particularly in the area of biomaterial selection for these applications as well as quantitative understanding of the process science. The strategic utilization of biological macromolecules provides a versatile approach to meet diverse requirements in 3D printing, such as printability, buildability, and biocompatibility. These molecules play a pivotal role in both physical and chemical cross-linking processes throughout the biofabrication, contributing significantly to the overall success of the 3D printing process. Among the several bioprintable materials, gelatin methacryloyl (GelMA) has been widely utilized for diverse tissue engineering applications, with some degree of success. In this context, this review will discuss the key bioengineering approaches to identify the gelation and cross-linking strategies that are appropriate to control the rheology, printability, and buildability of biomaterial inks. This review will focus on the GelMA as the structural (scaffold) biomaterial for different tissues and as a potential carrier vehicle for the transport of living cells as well as their maintenance and viability in the physiological system. Recognizing the importance of printability toward shape fidelity and biophysical properties, a major focus in this review has been to discuss the qualitative and quantitative impact of the key factors, including microrheological, viscoelastic, gelation, shear thinning properties of biomaterial inks, and printing parameters, in particular, reference to 3D extrusion printing of GelMA-based biomaterial inks. Specifically, we emphasize the different possibilities to regulate mechanical, swelling, biodegradation, and cellular functionalities of GelMA-based bio(material) inks, by hybridization techniques, including different synthetic and natural biopolymers, inorganic nanofillers, and microcarriers. At the close, the potential possibility of the integration of experimental data sets and artificial intelligence/machine learning approaches is emphasized to predict the printability, shape fidelity, or biophysical properties of GelMA bio(material) inks for clinically relevant tissues.

Regulation of Fluorescence and Self-assembly of a Salicylaldehyde Azine-Containing Amphiphile by Pillararene.

Regulation of fluorescence and self-assembly of a salicylaldehyde azine-containing amphiphile by a water-soluble pillar[5]arene via host-guest recognition in water was realized. The fluorescence and the self-assembled aggregates of the bola-type amphiphile G can be tailored by adding different amounts of water-soluble pillar[5]arene (WP5). In addition, the emission property and self-assembly behavior of G and WP5 are responsive to pH conditions. Furthermore, the fluorescence emission property of G and the regulation by WP5 or pH conditions was applied as information encryption material, rewritable paper, and erasable ink. We believe that this fluorescence regulation strategy is promising for the construction of advanced fluorescent organic materials.

Systematic Investigation on the Surfactant‐Assisted Liquid‐Phase Exfoliation of MoS2 and WS2 in Water for Sustainable 2D Material Inks

MoS2 and WS2 have gathered significant attention due to their tunable properties and wide range of applications. Liquid‐phase exfoliation (LPE) is a facile method to prepare 2D MoS2 and WS2. Currently, the principally employed solvents for LPE of MoS2 and WS2 are expensive and toxic, and have high boiling points. These drawbacks encourage to find more sustainable alternatives to the liquid medium used for the preparation of 2D material inks. Water is the best option, but surfactants are necessary for LPE in water, since MoS2 and WS2 are hydrophobic. Organic molecules with amphoteric character such as sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, and sodium hexadecyl sulfonate (SHS) are selected as suitable candidates for the role. However, the study of these surfactants used in LPE is barely systematically reported. In this work, a detailed investigation is presented on their impact on the LPE of MoS2 and WS2, which are representatives of transition‐metal dichalcogenides. By characterizing and qualifying the products from average number of layers, it is found that all the surfactants work efficiently to exfoliate MoS2 and WS2 into few layers, and SHS stabilizes the 2D layers better than the other two. However, in terms of yield and relative surfactant concentration, a real trade‐off is not identified between maximized quantity of exfoliated materials and minimized surfactant concentration, which prompts to select the colloidal ink based on the specific further needs for processing.

Biofabrication of nanocomposite-based scaffolds containing human bone extracellular matrix for the differentiation of skeletal stem and progenitor cells

Autograft or metal implants are routinely used in skeletal repair. However, they fail to provide long-term clinical resolution, necessitating a functional biomimetic tissue engineering alternative. The use of native human bone tissue for synthesizing a biomimetic material ink for three-dimensional (3D) bioprinting of skeletal tissue is an attractive strategy for tissue regeneration. Thus, human bone extracellular matrix (bone-ECM) offers an exciting potential for the development of an appropriate microenvironment for human bone marrow stromal cells (HBMSCs) to proliferate and differentiate along the osteogenic lineage. In this study, we engineered a novel material ink (LAB) by blending human bone-ECM (B) with nanoclay (L, Laponite®) and alginate (A) polymers using extrusion-based deposition. The inclusion of the nanofiller and polymeric material increased the rheology, printability, and drug retention properties and, critically, the preservation of HBMSCs viability upon printing. The composite of human bone-ECM-based 3D constructs containing vascular endothelial growth factor (VEGF) enhanced vascularization after implantation in an ex vivo chick chorioallantoic membrane (CAM) model. The inclusion of bone morphogenetic protein-2 (BMP-2) with the HBMSCs further enhanced vascularization and mineralization after only seven days. This study demonstrates the synergistic combination of nanoclay with biomimetic materials (alginate and bone-ECM) to support the formation of osteogenic tissue both in vitro and ex vivo and offers a promising novel 3D bioprinting approach to personalized skeletal tissue repair.Graphic abstract

Improving the Three-Dimensional Printability of Potato Starch Loaded onto Food Ink.

This study focuses on improving the 3D printability of pea protein with the help of food inks designed for jet-type 3D printers. Initially, the food ink base was formulated using nanocellulose-alginate with a gradient of native potato starch and its 3D printability was evaluated. The 3D-printed structures using only candidates for the food ink base formulated with or without potato starch exhibited dimensional accuracy exceeding 95% on both the X and Y axes. However, the accuracy of stacking on the Z-axis was significantly affected by the ink composition. Food ink with 1% potato starch closely matched the CAD design, with an accuracy of approximately 99% on the Z-axis. Potato starch enhanced the stacking of 3D-printed structures by improving the electrostatic repulsion, viscoelasticity, and thixotropic behavior of the food ink base. The 3D printability of pea protein was evaluated using the selected food ink base, showing a 46% improvement in dimensional accuracy on the Z-axis compared to the control group printed with a food ink base lacking potato starch. These findings suggest that starch can serve as an additive support for high-resolution 3D jet-type printing of food ink material.

Cell Patterning Using Magnetic-Archimedes Strategy.

Cell patterning, allowing precise control of cell positioning, presents a unique advantage in the study of cell behavior. In this protocol, a cell patterning strategy based on the Magnetic-Archimedes (Mag-Arch) effect is introduced. This approach enables precise control of cell distribution without the use of ink materials or labeling particles. By introducing a paramagnetic reagent to enhance the magnetic susceptibility of the cell culture medium, cells are repelled by magnets and arrange themselves into a pattern complementary to the magnet sets positioned beneath the microfluidic substrate. In this article, detailed procedures for cell patterning using the Mag-Arch-based strategy are provided. Methods for patterning single-cell types as well as multiple cell types for co-culture experiments are offered. Additionally, comprehensive instructions for fabricating microfluidic devices containing channels for cell patterning are provided. Achieving this feature using parallel methods is challenging but can be done in a simplified and cost-effective manner. Employing Mag-Arch-based cell patterning equips researchers with a powerful tool for in vitro research.

Design and development of dual-extruder food 3D printer based on selective compliance assembly robot arm and printing of various inks

Recent research in food 3D printing mainly focuses on ink materials, with relatively limited research on printer equipment development. Furthermore, the development of traditional food three-axis 3D printer is high cost and low productivity. In this study, we developed a dual extruder for food 3D printing, and designed a dual-extruder system based on Selective Compliance Assembly Robot Arm (SCARA) equipment. The productivity was determined by measuring significance analysis on the physical dimensions and the texture characteristics of the printed products using single/dual-extruder. A variety of food inks were experimented and various self-developed print paths were experimented with. The results of the two sets of significance analyses on physical dimensions and texture characteristics lead to the conclusion that the development of the dual-extruder system based on the SCARA machine arm successfully improved productivity. This also verified the broad adaptability of the device's inks, which operate on the principle of air pressure extrusion. We believe that this finding provides a new research direction for 3D printing of food products.

Multi-responsive smart fluorophores from pyrazole-functionalized tetraphenylethene AIEgens in response to Hg(II) ion, temperature, and mechanical force

Five tetraphenylethene (TPE) derivatives 1a, 1b, 2, 3, and 4 with adjustable stimuli-responsive characteristics were designed and synthesized in this study. Using single-crystal X-ray diffraction, the effects of substitution positions and pyrazolyl numbers on molecular packing were examined in the solid state. The findings indicate that as the pyrazolyl numbers increased, the molecular packing of the compound progressively changed from the C−H···π stacked compact mode in 1 − 3 to the X-crossing stacked loose mode in 4, which results in the origin of various stimuli-responsive phenomena in compound 4. This approach facilitates the preparation of multi-stimuli-responsive (thermochromism, mechanochromism, and metal ion fluorescence switch) smart fluorophores with tunable emission color. Moreover, compound 4, with an excellent fluorescence performance, exhibited three different colors when reversible mechanochromism was selected as the candidate for an optical recording material and security ink. This study proposes an effective method to guide the design of stimuli-responsive materials, which, in turn, would facilitate the development of high-contrast MC molecules, and the optical information anticounterfeiting based on grinding was proven by utilizing the grind-responsive luminescence capabilities.

Double-layered hydrogels based on phase change material and pen ink for continuous and efficient solar-driven seawater desalination

A novel double-layered hydrogel based on the polyacrylamide matrix, pen ink, and phase-change microcapsules was developed to construct a hydrogel-based evaporator for efficient and continuous seawater desalination. The n-eicosane (core)@crystalline TiO2 (shell) phase-change microcapsules were fabricated through interfacial polycondensation, and the resulting phase-change microcapsules obtained a considerably high latent-heat capacity of 187 J·g−1. The upper layer of the hydrogel exhibits a high solar absorptivity of over 90 % due to the introduction of pen ink as a solar absorber, which helps the hydrogel-based evaporator to gain an excellent photothermal energy conversion capability. A high evaporation efficiency of 93.89 % was obtained for the developed hydrogel-based evaporator along with a high evaporation rate of 1.85 kg·m−2·h−1 under one-sun illumination. The phase-change microcapsules dispersed in the lower layer of the hydrogel can act as a latent heat-storage unit to store a great quantity of photothermal energy through melting phase change by the phase change material core. This imparts a consecutive evaporation capability to the developed hydrogel-based evaporator. As a result, its water production was increased by 11 % under 50-min one-sun illumination and 50-min non-illumination.

Study on influence of ink material properties on deposited filaments in direct ink writing based on numerical simulations

Direct ink writing (DIW) is one of the most popular additive manufacturing (AM) techniques and deposited filament (DF) is one of the basic and critical elements in the process. Ink material properties have significant influence on DIW. However, influence of ink material properties on DF have not been fully studied. To address this barrier, in this paper, a three-dimensional (3D) numerical simulation model for DF was established through volume of fluid (VOF) method. And effect of ink material properties including viscosity properties and static contact angle on DF were studied based on the established numerical simulation model.

Inkjet Printing of Pharmaceuticals.

Inkjet printing (IJP) is an additive manufacturing process that selectively deposits ink materials, layer-by-layer, to create 3D objects or 2D patterns with precise control over their structure and composition. This technology has emerged as an attractive and versatile approach to address the ever-evolving demands of personalized medicine in the healthcare industry. Although originally developed for nonhealthcare applications, IJP harnesses the potential of pharma-inks, which are meticulously formulated inks containing drugs and pharmaceutical excipients. Delving into the formulation and components of pharma-inks, the key to precise and adaptable material deposition enabled by IJP is unraveled. The review extends its focus to substrate materials, including paper, films, foams, lenses, and 3D-printed materials, showcasing their diverse advantages, while exploring a wide spectrum of therapeutic applications. Additionally, the potential benefits of hardware and software improvements, along with artificial intelligence integration, are discussed to enhance IJP's precision and efficiency. Embracing these advancements, IJP holds immense potential to reshape traditional medicine manufacturing processes, ushering in an era of medical precision. However, further exploration and optimization are needed to fully utilize IJP's healthcare capabilities. As researchers push the boundaries of IJP, the vision of patient-specific treatment is on the horizon of becoming a tangible reality.

Inkjet‐Printed Flexible Thin‐Film Thermal Sensors for Detecting Elevated Temperature Range

All inkjet‐printed thermal sensors are manufactured based on a metal–insulator–metal (MIM) interface or capacitor architecture, for the adapted device size ranging from 16 to 36 mm2 active area. Two different material inks, namely a nanoparticle conductive silver ink and an inorganic‐polymer‐based hybrid insulator ink, are applied layer by layer on a thin flexible polyimide substrate, for developing the printed MIM devices. To ensure the desired electronic conductivity and insulation from the layers, the manufacturing process steps and parameters are tuned, accordingly. The results show that the inkjet‐printed MIM devices could constitute up to 15 μm thickness and demonstrate average detection of a change in electrical capacitance ranging from 20 to 100 pF, when the temperature is varied between 100 and 300 °C. The investigations also summarize that the change in the electrical response is enough to detect an increment of 50 °C. The printed sensors also display high operational stability and repeatability, when subjected to thermal cycling.

Screen printable PANI/carbide-derived carbon supercapacitor electrode ink with chitosan binder

Polyaniline (PANI)/carbide-derived carbon (CDC) was synthesized by using in-situ chemical oxidative polymerization of PANI in presence of CDC. Conductive electrode ink materials were prepared by using eco-friendly chitosan binder in water media. In the following, symmetrical supercapacitors (SCs) were fabricated by both doctor blade coating and screen printing technique. The electrical conductivity, morphology, specific capacitance, and energy density of these composites were evaluated for their applicability as SC electrodes. Pure PANI with chitosan binder was not printable because of its brittleness, however, the presence of CDC allows the preparation of smooth films which are suitable for electrode preparation. The fabricated composite electrode has a higher specific capacitance (up to 419 F g−1) and higher energy density (up to 6.7 W h kg−1) compared to the pristine CDC electrode. The capacitance of screen-printed SCs was 440–470 mF with an equivalent series resistance of about 27 Ω.

A study on the printability of manufactured sand concrete

3D printed concrete (3DPC) is a rapid construction technology that uses concrete as an ink material to build three-dimensional structures layer by layer, with the advantages in free formwork, complex buildings printing and cost savings. In this paper, the printability and mechanical properties of 3D printed manufactured sand concrete (3DPMSC) were tested with different binder-to-sand ratios. The optimal dosage of manufactured sand was clarified, and the effect of manufactured sand dosage on pore characteristics was studied using CT scanning technology. The test results indicate that as the binder-to-sand ratio increases, the flowability, open time and extrudability of 3DPMSC gradually decrease. Improved buildability is obtained within the binder-to-sand ratio range of 1:1.1 ∼ 1:1.3. In addition, the compressive and flexural strengths of the 3DPMSC increase as the binder-to-sand ratio decreases, and the mechanical strengths are optimal in the Z direction. The pore distribution in 3DPMSC significantly varies in directionality, with an increase in both pore volume and number. This research lays a foundation on the engineering application and science exploration of 3DPMSC.

Direct Write Printing of Ultraviolet-Curable Bulk Superhydrophobic Ink Material.

Although superhydrophobic surfaces have various promising applications, their fabrication methods are often limited to 2D plane surfaces that are vulnerable to abrasion and have limited adhesion to the substrate. Herein, an ultraviolet (UV) curable ink with bulk superhydrophobicity, consisting of poly(dimethylsiloxane) (PDMS) resins, hydrophobic silica, and solvent (porogen), was successfully developed for UV-assisted direct write printing processing. After UV curing of the ink followed by solvent evaporation, the generated porous structure cooperates with silica particles to form a self-similar and hierarchical structure throughout the bulk material, which can keep its original morphology even after cyclic abrasion (over 1000 times) and thus exhibits durable superhydrophobicity. With this unique ink, UV-assisted direct write printing can not only create 2D superhydrophobic surfaces on various substrates (e.g., paper and wire mesh) but also fabricate self-supporting 3D superhydrophobic objects for various applications such as waterproofing and oil-water separation. The printed objects exhibited a stable superhydrophobicity against liquid corrosion and mechanical damage. In addition, the 3D printing approach can be used to optimize the oil-water separation performance of the superhydrophobic porous materials by tuning the pore size, thus presenting promising applications.