Rheological Properties Of Inks Research Articles

Rheological insights into 3D printing of drug products: Drug nanocrystal-poloxamer gels for semisolid extrusion

The importance of ink rheology to the outcome of 3D printing is well recognized. However, rheological properties of printing inks containing drug nanocrystals have not been widely investigated. Therefore, the objective of this study was to establish a correlation between the composition of nanocrystal printing ink, the ink rheology, and the entire printing process. Indomethacin was used as a model poorly soluble drug to produce nanosuspensions with improved solubility properties through particle size reduction. The nanosuspensions were further developed into semisolid extrusion 3D printing inks with varying nanocrystal and poloxamer 407 concentrations. Nanocrystals were found to affect the rheological properties of the printing inks both by being less self-supporting and having higher yielding resistances. During printing, nozzle blockages occurred. Nevertheless, all inks were found to be printable. Finally, the rheological properties of the inks were successfully correlated with various printing and product properties. Overall, these experiments shed new light on the rheological properties of printing inks containing nanocrystals.

Processing and properties of aqueous protein/polysaccharide mixture-based inks for additive manufacturing

Three-dimensional (3D) food printing shows its enormous potential in customization of food designs and personalization of nutritional contents. Herein, two aqueous protein/polysaccharide food inks composed of gelatin B (GB)/xanthan gum (XG) and soy protein acid hydrolysate (SP)/XG, respectively, were investigated for material extrusion additive manufacturing. For both ink systems, processing maps were generated based on the relationship between nozzle diameter and XG concentration for different types of printed geometries including filament, 40-layer scaffolds and 3D complex structures (i.e., starfish). XG concentration was found to be strongly linked to ink rheological properties, thus influencing not only the flow behavior during the printing process, but also the shape fidelity and shape retention after deposition. Inks with 3GB/11XG (3 wt% GB/11 wt% XG) and 8SP/15XG (8 wt% SP/15 wt% XG) demonstrated the highest printability. Shape fidelity map for the post-deposition assessment of printed 3D structures proposed the appropriate range of viscoelastic properties through a well-defined shape fidelity index. Texture profile results also revealed that both polysaccharide concentration and protein type are critical to textural properties of the printed objects, guiding the choice of a suitable ink for an individual 3D food printing. Finally, according to the processing and shape fidelity maps previously defined, an 18-layer two-color 3D complex dolphin shape was successfully fabricated using both 3GB/11XG and 8SP/15XG food inks by a multi-material extrusion-based printing technique in one manufacturing process. This work provides comprehensive guidelines to design and fabricate 3D structures of aqueous protein/polysaccharide mixture-based inks to serve the purpose of accurately personalizing and diversifying nutrition for food applications.

Three-Dimensional Printed Shape Memory Gels Based on a Structured Disperse System with Hydrophobic Cellulose Nanofibers.

Inks for 3D printing were prepared by dispersing bacterial cellulose nanofibers (CNF) functionalized with methacrylate groups in a polymerizable deep eutectic solvent (DES) based on choline chloride and acrylic acid with water as a cosolvent. After 3D printing and UV-curing, the double-network composite gel consisting of chemically and physically crosslinked structures composed from sub-networks of modified CNF and polymerized DES, respectively, was formed. The rheological properties of inks, as well as mechanical and shape memory properties of the 3D-printed gels, were investigated in dynamic and static modes. It was shown that the optimal amount of water allows improvement of the mechanical properties of the composite gel due to the formation of closer contacts between the modified CNF. The addition of 12 wt% water results in an increase in strength and ultimate elongation to 11.9 MPa and 300%, respectively, in comparison with 5.5 MPa and 100% for an anhydrous system. At the same time, the best shape memory properties were found for an anhydrous system: shape fixation and recovery coefficients were 80.0 and 95.8%, respectively.

Scalable Production of Catecholamine-Densified MXene Coatings for Electromagnetic Shielding and Infrared Stealth.

Processing transition metal carbides/nitrides (MXenes) inks into large-area functional coatings expects promising potential for electromagnetic interference (EMI) shielding and infrared stealth. However, the coating performances, especially for scalable fabrication techniques, are greatly constrained by the flake size and stacking manner of MXene. Herein, the large-area production of highly densified and oriented MXene coatings is demonstrated by engineering interfacial interactions of small MXene flakes with catecholamine molecules. The catecholamine molecules can micro-crosslink MXene nanosheets, significantly improving the ink's rheological properties. It favors the shear-induced sheet arrangement and inhibition of structural defects in the blade coating process, making it possible to achieve high orientation and densification of MXene assembly by either large-area coating or patterned printing. Interestingly, the MXene/catecholamine coating exhibits high conductivity of up to 12 247 S cm-1 and ultrahigh specific EMI shielding effectiveness of 2.0 ×10 5 dB cm2 g-1 , obviouslysuperior to most of the reported MXene materials. Furthermore, the regularly assembled structure also endows the MXene coatings with low infrared emissivities for infrared stealth applications. Therefore, MXene/catecholamine coatings with ultraefficient EMI shielding and low infrared emissivity prove the feasibility of applications in aerospace, military, and wearable devices.

Water Influence on the Physico-Chemical Properties and 3D Printability of Choline Acrylate-Bacterial Cellulose Inks.

The aim of this work was to study the influence of water as a co-solvent on the interaction between a polymerizable ionic liquid-choline acrylate (ChA)-and bacterial cellulose. Bacterial cellulose dispersed in ChA is a new type of UV-curable biopolymer-based ink that is a prospective material for the 3D printing of green composite ion-gels. Higher cellulose content in inks is beneficial for the ecological and mechanical properties of materials, and leads to increased viscosity and the yield stress of such systems and hampers printability. It was found that the addition of water results in (1) a decrease in the solvent viscosity and yield stress; and (2) a decrease in the stability of dispersion toward phase separation under stress. In this work, an optimal composition in the range of 30-40 wt% water content demonstrating 97-160 Pa of yield stress was found that ensures the printability and stability of inks. The rheological properties of inks and mechanical characteristics (0.7-0.8 MPa strength and 1.1-1.2 MPa Young's modulus) were obtained. The mechanism of influence of the ratio ChA/water on the properties of ink was revealed with atomic force microscopy, wide-angle X-ray diffraction studies of bacterial cellulose after regeneration from solvent, and computer simulation of ChA/water mixtures and their interaction with the cellulose surface.

Eucalyptus bleached kraft pulp-ionic liquid inks for 3D printing of ionogels and hydrogels

3D printing has been recently recognized as one of the most promising technologies due to the multiple options to fabricate cost-effective and customizable objects. However, the necessity to substitute fossil fuels as raw materials is increasing the research on bio-based inks with recyclable and eco-friendly properties. In this work, we formulated inks for the 3D printing of ionogels and hydrogels with bleached kraft pulp dissolved in [Emim][DMP] at different concentrations (1–4 wt%). We explored each ink's rheological properties and printability and compared the printability parameters with a commercial ink. The rheological results showed that the 3 % and 4 % cellulose-ionic liquid inks exhibited the best properties. Both had values of damping factor between 0.4 and 0.7 and values of yield stress between 1900 and 2500 Pa. Analyzing the printability, the 4 wt% ink was selected as the most promising because the printed ionogels and the hydrogels had the best print resolution and fidelity, similar to the reference ink. After printing, ionogels and hydrogels had values of the elastic modulus (G′) between 103 and 104 Pa, and the ionogels are recyclables. Altogether, these 3D printed cellulose ionogels and hydrogels may have an opportunity in the electrochemical and medical fields, respectively.

Ink Design Enabling Slot‐Die Coated Perovskite Solar Cells with >22% Power Conversion Efficiency, Micro‐Modules, and 1 Year of Outdoor Performance Evaluation

AbstractThe next technological step in the exploration of metal‐halide perovskite solar cells is the demonstration of larger‐area device prototypes under outdoor operating conditions. The authors here demonstrate that when slot‐die coating the halide perovskite layers on large areas, ribbing effects may occur but can be prevented by adjusting the precursor ink's rheological properties. For formamidinium lead triiodide (FAPbI3) precursor inks based on 2‐methoxyethanol, the ink viscosity is adjusted by adding acetonitrile (ACN) as a co‐solvent leading to smooth FAPbI3 thin‐films with high quality and layer homogeneity. For an optimized content of 46 vol% of the ACN co‐solvent, a certified steady‐state performance of 22.3% is achieved in p‐i‐n FAPbI3‐perovskite solar cells. Scaling devices to larger areas by making laser series‐interconnected mini‐modules of 12.7 cm2, a power conversion efficiency of 17.1% is demonstrated. A full year of outdoor stability testing with continuous maximum power point tracking on encapsulated devices is performed and it is demonstrated that these devices maintain close to 100% of their initial performance during winter and spring followed by a significant performance decline during warmer summer months. This work highlights the importance of the real‐condition evaluation of larger area device prototypes to validate the technological potential of halide perovskite photovoltaics.

Effect of dispersant on catalyst ink properties and catalyst layer structure for high performance polymer electrolyte membrane fuel cells

Here, catalyst ink is prepared using a dispersant with the hydrophile-lipophile balance (HLB) value of 17. The effects of the ionomer-catalyst agglomerate size on the ink rheological properties, and subsequent catalyst layer (CL) microstructure and electrochemical performance are investigated to elucidate the relationship between ink properties and cell performance. Results shows that the smallest agglomerate size (2.7 μm) and polydispersity index (PDI, 0.068) are obtained with 1 wt% dispersant content; the low PDI indicate that the ink is well dispersed. Steady-state and thixotropy tests also show that the ink has shear-thinning and gel-like behavior (Recovery ratio: 30.4%). It is proposed that this occurs because the agglomerates are smaller and the interaction forces between them increase. Thus, the ink structure is maintained until the dried CL is formed, and as a result, the pore volume of CL with 1 wt% dispersant is increased compared to those with 0 and 9 wt%. In addition, the 1 wt% CL-based MEA shows the highest performance (1224.4 mA cm−2 at 100% RH) owing the increase in the number of channels (1190 mA cm−2 in four-channel) and back pressure (1240 mA cm−2 at 1.5 barca).

Investigation and effect on 3D printing quality of surimi ink during freeze-thaw cycles by antifreeze peptides

Frozen storage of 3D printing ink is an inevitable trend, but it may impair the processing properties of surimi ink. Antifreeze peptides (AFPs) show potential application foreground in 3D printing. In this study, the rheological properties in 3D printing extrusion, recovery and stabilization stage were investigated of surimi ink with AFPs during FT cycles, and linking the printability, resolution and shape fidelity, respectively. Moreover, the evaluation method of 3D printing quality during freeze-thaw (FT) cycles including printability, resolution, and shape fidelity of surimi ink after FT was firstly established by the line of suspension and 1D patterns, 2D patterns, and 3D models. The results showed that the rheological properties of ink were significantly improved due to optimum addition of AFPs during FT cycles. The yield stress ( τ 0 ), consistency index ( K ), and shear-thinning index ( n ), of 2% AFPs ink at FT 4 times were 185.93 Pa, 2.506 × 10 5 Pa•s n , and 0.062, respectively, in the extrusion stage. In the recovery stage, the recovery time (T) and gelation time (Tgel) were 26.14 s and 174.83 s. In the stabilization stage, the ink has properties similar to solids, the interaction strength of molecular ( A ) and the number of molecular interactions ( z ) were 1.994 × 10 3 Pa s 1/z and 9.488. It demonstrated best printability, resolution, and shape fidelity, even supporting 23-layer 3D printing structures. This research firstly constructed a new approach for the application of AFPs in 3D printing of frozen foods. • The evaluation method of ink printing quality was firstly constructed. • Rheological properties and print quality were influenced by FT cycles. • 2% AFP ink is the optimum formulation for 3D printing after FT cycles. • Suspension line is a quantitative indicator of continuous printing.

Embedded 3D printing of dilute particle suspensions into dense complex tissue fibers using shear thinning xanthan baths.

In order to fabricate functional organoids and microtissues, a high cell density is generally required. As such, the placement of cell suspensions in molds or microwells to allow for cell concentration by sedimentation is the current standard for the production of organoids and microtissues. Even though molds offer some level of control over the shape of the resulting microtissue, this control is limited as microtissues tend to compact towards a sphere after sedimentation of the cells. 3D bioprinting on the other hand offers complete control over the shape of the resulting structure. Even though the printing of dense cell suspensions in the ink has been reported, extruding dense cellular suspensions is challenging and generally results in high shear stresses on the cells and a poor shape fidelity of the print. As such, additional materials such as hydrogels are added in the bioink to limit shear stresses, and to improve shape fidelity and resolution. The maximum cell concentration that can be incorporated in a hydrogel-based ink before the ink's rheological properties are compromised, is significantly lower than the concentration in a tissue equivalent. Additionally, the hydrogel components often interfere with cellular self-assembly processes. To circumvent these limitations, we report a simple and inexpensive xanthan bath based embedded printing method to 3D print dense functional linear tissues using dilute particle suspensions consisting of cells, spheroids, hydrogel beads, or combinations thereof. Using this method, we demonstrated the self-organization of functional cardiac tissue fibers with a layer of epicardial cells surrounding a body of cardiomyocytes.

Preparation of photoluminescent nanocomposite ink for detection and mapping of fingermarks.

Simple and efficient detection and mapping method based on a strong turn-on fluorescent pigment was developed for fingerprint analysis. We present a phosphor powder characterized by strong emission which is useful to achieve better fingerprint detection on multicolored or photoluminescent surfaces, such as currency notes characterized by optically changeable inks and highly fluorescent positions, because it offers better contrast and reduce the difficulty of background interference. Novel photochromic ink was prepared to establish a fingerprinted colorless film onto cellulose documents with green emission for anticounterfeiting applications as illustrated by photoluminescence spectra. Inorganic/organic nanoscale composite ink was prepared from rare-earth doped aluminate phosphor nanoparticles (PNPs; 27-49 nm) dispersed in a polyacrylic acid binding agent. PNPs were dispersed efficiently in polyacrylic acid to generate a colorless mark. The produced photochromic inks were spray-coated onto off-white paper sheets enclosing invisible fingermarks, and then exposed to thermofixation. Photochromic film was detected on paper surface presenting a transparent appearance under visible daylight and switchable to green under UV light. The CIE Lab parameters and photoluminescence spectra were studied under visible light and ultraviolet irradiation. The fingerprinted sheets showed fluorescence band at 517 nm upon excitation at 366 nm, showing a bathochromic shift and reversible photochromism without fatigue. The morphologies of pigment phosphor particles and fingerprinted sheets were inspected. The rheological properties of ink and mechanical behavior of the fingerprinted paper samples were explored. HIGHLIGHTS: Novel smart ink with alkaline-earth aluminate and polyacrylic acid was developed. Dual-mode fluorescent photochromism was presented for latent fingerprint analysis. Off-white fingerprinted films under daylight showed color change to green under UV. Fluorescence band monitored at 517 nm upon excitation at 366 nm. Fluorescent fingermark on paper sheets demonstrated good photostability.

Direct Ink Writing of AISI 316L Dense Parts and Porous Lattices

The focus of the present work is the development of a metallic ink that possesses controlled rheological properties: by keeping printing parameters constant both AISI 316L dense parts and porous scaffolds have been produced. Shrinkage, porosity, and mechanical properties have been studied to evaluate the link between the ink rheological properties and the final part. Depending on binder composition, linear shrinkage ranging from 9% to 22% and porosity from 34 to 7 vol% are measured. Tensile strength for specimens sintered at 1240 °C reach the value of 444 MPa and elongation at a break of 12.3%. These values are still far from additively manufactured AISI 316L parts with powder bed fusion technologies, but represent an improvement compared to previously reported data in the literature for AISI 316L parts 3D printed by DIW. Porous scaffolds with a spanning distance of 1.2 mm are printed and sintered. Porosity of 74 vol% and compression strength of 74 MPa are measured for this set of samples showing how the produced ink represents a valuable alternative to pastes already present in the literature.

3D Bioprinted Hydroxyapatite or Graphene Oxide Containing Nanocellulose-Based Scaffolds for Bone Regeneration.

Bone tissue is usually damaged after big traumas, tumors, and increasing aging-related diseases such as osteoporosis and osteoarthritis. Current treatments are based on implanting grafts, which are shown to have several inconveniences. In this regard, tissue engineering through the 3D bioprinting technique has arisen to manufacture structures that would be a feasible therapeutic option for bone regenerative medicine. In this study, nanocellulose-alginate (NC-Alg)-based bioink is improved by adding two different inorganic components such as hydroxyapatite (HAP) and graphene oxide (GO). First, ink rheological properties and biocompatibility are evaluated as well as the influence of the sterilization process on them. Then, scaffolds are characterized. Finally, biological studies of embedded murine D1 mesenchymal stem cells engineered to secrete erythropoietin are performed. Results show that the addition of both HAP and GO prevents NC-Alg ink from viscosity lost in the sterilization process. However, GO is reduced due to short cycle autoclave sterilization, making it incompatible with this ink. In addition, HAP and GO have different influences on scaffold architecture and surface as well as in swelling capacity. Scaffolds mechanics, as well as cell viability and functionality, are promoted by both elements addition. Additionally, GO demonstrates an enhanced bone differentiation capacity.

Effects of spatial and temporal offset during landing on mixing performance in intersecting-jets printing

Intersecting-jets printing extends the inkjet printing capability to allow the deposition of different materials using a printing-then-mixing approach. This study focuses on the analysis of the robustness of mixing performance under spatial and temporal offset conditions during intersecting-jets printing and how this robustness is affected by the ink rheological properties and reactivity. Reactive sodium alginate and calcium chloride solutions have been used as the model materials. Shannon’s entropy has been used to measure the mixing efficiency, and high-speed imaging and particle image velocimetry have been used to characterize the ink motion after intersecting collision and landing onto a receiving substrate to better understand its mixing dynamics. While optimal mixing performance (> 90%) can be obtained under ideal printing conditions, the presence of a spatial offset may result in a smaller post-landing velocity but it may not affect significantly the time required to reach an equilibrium state depending on ink materials used. The spatial offset may induce a negative effect on the mixing performance, and selecting a less viscous or low reactivity ink can largely attenuate the effects of spatial offset on the mixing performance. Due to the gelation of the first deposited droplet, even small temporal offsets, on the order of 0.5 – 2.0 ms, may still lead to inconsistencies in the mixing performance. While the intersecting-jets printing process is a complicated process that may involve complex fluids as inks, the mixing performance can still be satisfactorily predicted by using an artificial neural network-based modeling approach.

Ink Rheology Regulates Stability of Bioprinted Strands.

Three-dimensional (3D) extrusion bioprinting typically requires an ad hoc trial-and-error optimization of the ink composition toward enhanced resolution. The ink solutions are solidified after leaving cone-shaped or cylindrical nozzles. The presence of ink instability not only hampers the extrusion resolution but also affects the behavior of embedded cellular components. This is a key factor in selecting (bio)inks and bioprinting design parameters for well-established desktop and handheld bioprinters. In this work, we developed an analytical solution for the process of ink deposition and compared its predictions against numerical simulations of the deposition. We estimated the onset of ink instability as a function of ink rheological properties and nozzle geometry. Our analytical results suggest that enhancing the shear-thinning behavior of the ink shortens the toe region of the deposition. Such an extrusion process is often desired, as it leads to faster depositions. However, we demonstrated that such conditions increase the possibility of lateral buckling of the strand once touching the substrate defined as instability in this study. The present study serves as a benchmark for detailed simulations of the extrusion process for optimal bioprinting.

Two-dimensional Material based Printed Photonics: A Review

Abstract Functional inks based on two-dimensional (2D) materials have potential application in building new and commercially viable photonic devices via different printing techniques. Printed photonics using 2D material-based inks brings together the unique optical properties of 2D materials via different printing techniques for fabricating photonic devices that can revolutionize various sectors in telecommunication, information technology, sensors and computing. Understanding the need for a comprehensive guide for researchers in the field of printed photonics based on 2D material inks, we have brought together the essential concepts in this field. The review begins with discussion on optical properties of commonly used 2D materials in photonic applications. Since different printing techniques demand different ink rheological properties for efficient printing, we have discussed it for different printing techniques. The substrates compatible for printed photonics application are also listed. Mechanisms of common printing methods in device fabrication are explained with more focus on the most commonly demonstrated method in printed photonics, i.e., inkjet printing. We have discussed a few examples of photonic devices where printed photonics is already demonstrated with 2D material functional inks. Finally, our perspective on future prospects of 2D materials, with excellent optical properties, that are yet to be formulated into inks for new and efficient photonic device fabrication as well as devices with potentially new functionalities are listed.

Rubber ink formulations with high solid content for direct-ink write process

Additive manufacturing (AM) is a potential technology for future applications such as smart devices and airless tires. Natural rubber, which is used with restricted processing methods in the tire industry, has drawbacks for use in AM technology because of the high pressure and temperatures required to process it. The motivation of this study is to determine if natural rubber can be used as a 3D printable material. To this end, natural rubber latex (NL) was used as the basis for a printable ink. Liquid rubber was introduced to the NL in various amounts to increase the amount of solid in the ink so as to improve its 3D printability and prevent shrinkage, and sulfur and other additives were incorporated into the mixture to facilitate vulcanization. The rheological properties of inks were investigated for consistent extrusion as well as for shape retention in the printed parts. Dimensional accuracy, printability, and mechanical properties of 3D printed specimens have been investigated. Using a direct-print AM system and the developed rubber ink, various 3D structures were fabricated to demonstrate that the developed ink could be a candidate for future rubber applications.

Optimization of Hybrid Ink Formulation and IPL Sintering Process for Ink-Jet 3D Printing.

Ink-jet 3D printing technology facilitates the use of various materials of ink on each ink-jet head and simultaneous printing of multiple materials. It is suitable for manufacturing to process a complex multifunctional structure such as sensors and printed circuit boards. In this study, a complex structure of a SiO2 insulation layer and a conductive Cu layer was fabricated with photo-curable nano SiO2 ink and Intense Pulsed Light (IPL)-sinterable Cu nano ink using multi-material ink-jet 3D printing technology. A precise photo-cured SiO2 insulation layer was designed by optimizing the operating conditions and the ink rheological properties, and the resistance of the insulation layer was 2.43 × 1013 Ω·cm. On the photo-cured SiO2 insulation layer, a Cu conductive layer was printed by controlling droplet distance. The sintering of the IPL-sinterable nano Cu ink was performed using an IPL sintering process, and electrical and mechanical properties were confirmed according to the annealing temperature and applied voltage. Then, Cu conductive layer was annealed at 100 °C to remove the solvent, and IPL sintered at 700 V. The Cu conductive layer of the complex structure had an electrical property of 29 µΩ·cm and an adhesive property with SiO2 insulation layer of 5B.

Microstructural design of printed graphite electrodes for lithium-ion batteries

Performance properties of lithium-ion battery electrodes; capacity, rate and lifetime, are determined by the design of the coating composite microstructure. The internal pore structure and electronic networks for high coat weight graphite electrodes are manipulated through changes in the ink rheological properties, and through an syringe dispensing printing process. The rheological properties of a water-based, high viscosity graphite ink were optimised using a secondary solvent for the rheological requirements of a syringe dispensing method. The microstructure of high coat-weight battery electrodes produced from printing and tape cast methods were compared and the electrochemical performance evaluated. Cross sectional analysis of the slurry cast coatings showed improved component homogeneity, lower graphite alignment with 0.1% to 10% weight increase of the secondary solvent, with a corresponding change in tortuosity of the electrodes of 5.3–2.8. Improved cycle life is observed with a printed electrode containing an embedded electrolyte channel. Performance properties were elucidated through charge discharge, GITT and PEIS measurements. Improved electronic conductivities, exchange currents and diffusion coefficients were observed for the syringe deposited electrode. This digital deposition process for manufacturing electrodes shows promise for further optimisation of electrodes for long-life, high energy density batteries.

Study on ink flow of silicone rubber for direct ink writing

AbstractDirect ink writing of soft materials is a very promising technology in 3D printing, and the rheological properties of inks are crucial for successful printing. In this paper, the effect of the rheological properties on the printing process of silicone rubber inks is studied to lay a foundation for the configurations of 3D printing process parameters. Also, the shape retention of the printing filaments is studied to provide a basis for the viscosity deployment of the inks. In addition, by studying the die swell ratio of nano‐silica‐reinforced silicone rubber inks at normal printing speed, it is found that the die‐swell ratio is proportional to the ink's relaxation time. Finally, the influence of the configuration of the short‐nozzle on the die swell is investigated, and the concave nozzle has a smaller extrusion swelling effect than the convex nozzle and the conical nozzle, providing new ideas for the adjustment of the filament diameter.