Printing Ink 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.

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.

Development of a pH-responsive intelligent label using low molecular weight chitosan grafted with phenol red for food packaging applications

In this study, we successfully developed a screen-printed pH-responsive intelligent label using low molecular weight chitosan grafted with phenol red (LCPR) as a colorant for screen printing ink. The LCPR was synthesized via a Mannich reaction, and its successful grafting was confirmed through FT-IR, UV–vis, and NMR spectroscopy. The LCPR exhibited lower crystallinity and thermal stability compared to low molecular weight chitosan (LC) and demonstrated zwitterionic behavior. To create intelligent labels, the LCPR-based ink was efficiently printed on cotton substrates with high resolution. The label exhibited remarkable sensitivity to buffer pH solutions and ammonia gas, leading to distinctive color changes from orange to red to purple. Additionally, the label showed excellent reversibility, storage stability, and leaching resistance to different food simulant solutions. The label was utilized to monitor shrimp freshness, successfully detecting a noticeable color shift upon spoilage. These findings highlight the significant potential of the LCPR-based label as an intelligent food packaging solution, offering pH-responsiveness and color stability for qualitative freshness detection of protein-rich food.

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.

Pimobendan controlled release guar gum printlets: Tailoring drug doses for personalised veterinary medicines

Treating chronic heart diseases in dogs is challenging due to variations in mass within and between species. Pimobendan (PBD), a veterinary drug only, is prescribed in specific cases of chronic heart disease in dogs and is available on the market in only a few different doses. Furthermore, the therapy itself is challenging due to the large size of the chewable tablets and the requirement for twice-daily administration. The development of customised and on-demand PBD medicines by three-dimensional (3D) printing has been proposed to circumvent these disadvantages. In this study, we designed controlled-release flavoured printlets containing PBD. We evaluated the use of two natural polymers, guar or xanthan gums, as the main component of the printing inks. Guar gum showed the better rheological behavior and printability by semisolid extrusion. The printlets were produced in three different shapes and sizes to allow dose customisation. Guar gum printlets showed a PBD controlled release profile, regardless of their shape or size. Therefore, we have demonstrated a novel approach for controlling PBD drug release and tailoring the dose by employing a natural polymer to produce 3D-printed tablets. This study represents a significant step towards the development of 3D-printed guar gum controlled-release formulations for veterinary applications.

Hydrogel Ink for 3D Printing with High and Widely Tunable Mechanical Properties via the Salting‐Out Effect

AbstractDue to the difficulty of simultaneously ensuring printability and controlling their mechanical properties, 3D printed hydrogels thus far have low modulus, far less than that of many biological tissues and organs. Therefore, their feasibility toward various biomimetic applications is currently limited. Herein, Direct‐Ink‐Writing (DIW) based 3D printable hydrogel ink with broadly adjustable mechanical properties is introduced. The salting‐out effect is utilized to effectively lower the gelation temperature of hydrogel inks with a wide range of modulus (0.193–1.072 MPa), making them all 3D printable. As a proof of concept, multi‐layered synthetic blood vessels that mimic the mechanical properties of biological blood vessels are printed, and their practicability toward surgical training is demonstrated. The versatility and simplicity of this technique make it highly promising for use in various 3D‐printed hydrogel biomaterials applications.

Considering cell viability in 3D printing of structured inks: A comparative and equivalent analysis of fluid forces

In conventional extrusion-based three-dimensional (3D) printing (E3DP), smaller needles reduce cell viability due to increased fluid forces like pressure and shear stress. A novel E3DP approach has emerged, involving 3D printing with structured inks. Fluid forces in both conventional and structured ink-based methods were evaluated through computational fluid dynamics (CFD) simulations. By employing 18G needles, we showcased the advantages of structured inks, including 2-symmetric, 4-symmetric, vascular-like, and hepatic lobule analogue-like inks, which demonstrated consistently lower pressures and shear stress compared with conventional inks. Specifically, vascular-like inks with a 2:1:1 extruded fiber layer distance showed significantly lower shear stress (average 6.595e+0 Pa, maximum 2.069e+2 Pa) than conventional methods. Equivalent analyses explored commonly used symmetric and core–shell inks, examining fluid forces on cells. Particularly, in core–shell inks with a 2.8 mm core layer radius, cells in the flow domain of the shell layer experienced an equivalent viscosity of 3.70 Pa·s, while in the core layer, it was 1.72 Pa·s. The analyses revealed a positive correlation between equivalent homogeneous ink viscosity and shear stress. The proposed workflow, emphasizing cell viability, offers an efficient approach for structured ink design. Also, experiments that used vascular-like ink-based printing as an example indicated significantly higher cell viability when compared with conventional printing. This research provides valuable insights for enhancing cell viability in 3D printing and advancing printing material design.

3D printing of cyanate ester resins with interpenetration networks for enhanced thermal and mechanical properties

AbstractCyanate ester (PT‐30) resin possesses exceptional thermal and mechanical properties, including high heat distortion temperature, high glass transition temperature (Tg), and outstanding mechanical characteristics. Conversely, the Tg of the homopolymer of tris(2‐hydroxyethyl)isocyanurate triacrylate (T‐acrylate) surpasses that of other acrylates. The combination of PT‐30 and T‐acrylate results in the formation of an interpenetrating polymer network (IPN) through a dual curing mechanism. Furthermore, the combination of these two polymers enables the tuning of rheology for shear thinning behavior for Ink Extrusion 3D printing technology by adjusting the amount of photoinitiator and rheological modifier. Here, 3D printable ink was formulated using PT‐30, T‐acrylate with a higher Tg, a photoinitiator, and a powdered rheological additive. The printed structures underwent a dual‐curing process involving exposure to UV light and thermal curing. Thermomechanical properties of the printed samples were characterized using dynamic mechanical analysis, thermogravimetric analysis, and tensile testing. The successful formation of an IPN structure through the polymerization of T‐acrylate and PT‐30 was observed, resulting in improved mechanical properties and an elevated Tg. The Fourier transform infrared spectroscopy analysis verified the formation of cross‐linked samples. Overall, this study demonstrates the feasibility of Ink Extrusion 3D printing, using a cyanate ester resin and tris(2‐hydroxyethyl)isocyanurate triacrylate with a dual‐curing mechanism. The enhanced mechanical properties at elevated temperatures (~80% retention of room temperature tensile strength at 200°C for sample with 70/30 wt%) and high Tg of 349 ± 3°C for printed structures shown in this study make them suitable for high‐performance structural applications in industries such as aerospace, defense, and microelectronics.

3D printed emulsion based on arginine-myofibrillar protein

The feasibility of preparing high internal phase Pickering emulsions (HIPPEs) from arginine (Arg) and tilapia myofibrillar protein (MP) complex particles for 3D printing was investigated. The characterization of Arg-MP solutions showed that the Arg-MP complexes had excellent emulsification potential. HIPPE stabilized by Arg-MP had a strong self-supporting and stable gel structure. Therefore, HIPPE stabilized by Arg-MP showed excellent stability. Furthermore, the viscoelasticity and thixotropic recovery of the Arg-MP-stabilized HIPPEs increased with increasing Arg concentrations. This made them suitable for 3D printing. Notably, the Arg-MP stabilized HIPPEs exhibited the best printing precision shape, resolution, and clear contours in 3D printing at an Arg concentration of 0.5 wt%. Our results provide a valuable source of food-grade materials for 3D printing inks and demonstrate a promising strategy for deep processing of tilapia myofibrillar protein.

Comparative study of print quality attributes on bio-based biodegradable plastic using flexography and gravure printing process

Printing has revolutionized not only the religious and educational world by providing printing on paper but also the commercial world by providing end-to-end solutions for packaging by printing on materials like plastics. Print quality refers to level of details and sharpness of printed products for wider acceptability. Print quality has an important role in maintaining consistency during printing on selected surfaces to provide desired satisfaction. Printability and runnability of substrates, substrate surface characteristics, and printing ink properties are attributes of print quality and are considered important for determining good quality printing. Solid ink density (SID), Hue error, grayness and ink trapping are some of the important measurable printability factors that play an important role in determining the print quality irrespective of substrates. Gravure printing and flexography printing are high-speed printing suitable for printing on flexible substrates so, attempts were made for explore the mutual compatibilities of new-generation printing substrates with established printing processes, which will prove to be a boon in the future by replacing conventional plastics with bio-based biodegradable plastics in printing for packaging and its other applications. So, multi-color printing on selected bio-based biodegradable plastics were explored for determining printability by measuring and maintaining print quality attributes during print runs.

Removal of Congo red dye from industrial effluents using metal oxide-clay nanocomposites: Insight into adsorption and precipitation mechanisms

The efficacy of magnesium oxide (MgO)-bentonite clay nanocomposite particles (MgO nanoparticles embedded in powdered bentonite clay) for water and wastewater treatment applications is examined herein. Congo red (CR), a widely used azo dye, was used as the model contaminant. For CR concentrations ≤120 mg/L, the optimum nanocomposite dosage was ≤1 g/L, achieving CR removal ≥99% for contact times (mixing durations) ≤10 min, whereas temperature and pH had no significant effect on the treatment process. The removal of CR dye followed the pseudo-second-order model than the first order model. Furthermore, adsorption isotherms followed the Langmuir adsorption isotherm rather than the Freundlich adsorption isotherm (R2 ≥ 0.99), hence confirming monolayer homogenous adsorption. The surface morphological and physicochemical characteristics of the nanocomposite were also identified, and results suggest that CR removal was governed by electrostatic attraction between the protonated hydroxyl groups (i.e., -OH2+), embedded on the nanocomposite surface, and the negatively charged –SO3-groups of the CR dye. When used for the treatment of real printing ink wastewater, CR was practically removed (⁓100%), whereas for real printing and dyeing wastewater (PDW), a more challenging effluent that also contains salts and other contaminants, CR removal was ≥80%. Overall, the produced MgO-bentonite clay nanocomposite hold great promise for sustainable CR removal, a typical contaminant that is released by many industries including printing, tannery and textile, paper, plastic, and paint and coatings.

A Molecular Rheology Dynamics Study on 3D Printing of Liquid Crystal Elastomers.

This work presents a rheological study of a biocompatible and biodegradable liquid crystal elastomer (LCE) ink for three dimensional (3D) printing. These materials have shown that their structural variations have an effect on morphology, mechanical properties, alignment, and their impact on cell response. Within the last decade LCEs are extensively studied as potential printing materials for soft robotics applications, due to the actuation properties that are produced when liquid crystal (LC) moieties are induced through external stimuli. This report utilizes experiments and coarse-grained molecular dynamics to study the macroscopic rheology of LCEs in nonlinear shear flow. Results from the shear flow simulations are in line with the outcomes of these experimental investigations. This work believes the insights from these results can be used to design and print new material with desirable properties necessary for targeted applications.

3D Printing of Anisotropic Piezoresistive Pressure Sensors for Directional Force Perception.

Anisotropic pressure sensors are gaining increasing attention for next-generation wearable electronics and intelligent infrastructure owing to their sensitivity in identifying different directional forces. 3D printing technologies have unparalleled advantages in the design of anisotropic pressure sensors with customized 3D structures for realizing tunable anisotropy. 3D printing has demonstrated few successes in utilizing piezoelectric nanocomposites for anisotropic recognition. However, 3D-printed anisotropic piezoresistive pressure sensors (PPSs) remain unexplored despite their convenience in saving the poling process. This study pioneers the development of an aqueous printable ink containing waterborne polyurethane elastomer. An anisotropic PPS featuring tailorable flexibility in macroscopic 3D structures and microscopic pore morphologies is created by adopting direct ink writing 3D printing technology. Consequently, the desired directional force perception is achieved by programming the printing schemes. Notably, the printed PPS demonstrated excellent deformability, with a relative sensitivity of 1.22 (kPa*wt. %)-1 over a substantial pressure range (2.8 to 8.1kPa), approximately fivefold than that of a state-of-the-art carbon-based PPS. This study underscores the versatility of 3D printing in customizing highly sensitive anisotropic pressure sensors for advanced sensing applications that are difficult to achieve using conventional measures.

Stabilizing effect of silver carp myofibrillar protein modified by high intensity ultrasound on high internal phase emulsions: Protein denaturation, interfacial adsorption and reconfiguration

This study evaluated the impact of high intensity ultrasound (HIU) on myofibrillar proteins (MP) from silver carp, and investigated the stabilizing effect of HIU-treated MP (UMP) on high internal phase emulsions (HIPEs). Ultrasonic cavitation induced protein denaturation by decreasing size and unfolding conformation, to expose more hydrophobic groups, particularly UMP at 390 W, showing the smallest particle size (181.71 nm) and most uniform distribution. These structural changes caused that UMP under 390 W exhibited the highest surface hydrophobicity, solubility (92.72 %) and emulsibility (115.98 m2/g and 70.4 min), all of which contributed to fabricating stable HIPEs with oil volume fraction up to 0.8. UMP-based HIPEs possessed tightly packed gel network and self-supporting appearance due to the adsorption of numerous proteins at the oil-water interface and the reduction of interfacial tension by protein reconfiguration. The larger interface coverage reinforced cross-linking between interfacial proteins, thus increasing the viscoelasticity and recoverability of HIPEs, also the resistance to centrifugal force, high temperature (90 °C, 30 min) and freeze-thaw cycles. These findings furnished insightful perspectives for MP deep processing through HIU, expanding the high-value application of UMP-based HIPEs in fat replacer, nutritional delivery system with high encapsulation content and novel 3D printing ink.

Multi‐Scale Design of Metal–Organic Framework Metamaterials for Broad‐Band Microwave Absorption

AbstractThe development of nanocomposite microwave absorbers is a critical strategy for tackling electromagnetic pollution. However, challenges persist regarding material stability and achieving broadband absorption. Herein, a novel multi−scale design approach for metamaterial absorbers is proposed. First, a series of bimetallic (cobalt and copper) semiconductive metal–organic framework (SC−MOF) crystals with atomically resolved structures are successfully prepared to serve as building blocks for metamaterials. By simply adjusting the concentration ratio of the two ions, the controllable preparation of crystal morphology can be achieved. This enables to precisely tune the absorption peak and bandwidth range of the SC−MOF, resulting in excellent EMW absorption performance (effective absorption bandwidth: 6.16 GHz, minimum reflection loss: −61 dB). Based on this, printable inks are further constructed by encapsulating the SC−MOF in polydimethylsiloxane and 3D‐printed multi−layered metamaterial absorbers based on woodpile porous architecture. The metamaterial absorber demonstrates a near‐perfect absorption in the microwave spectrum (with a bandwidth of 11.33 GHz), closely matching theoretical simulations. This multi−scale design approach, combining precise MOF materials construction with topological structure design, offers new insights for the development of broadband microwave absorbers.

Two-dimensional (2D) materials for 3D printed micro-supercapacitors and micro-batteries

Two-dimensional (2D) materials display a unique set of physical/chemical properties and are considered potential building blocks for the manufacturing of microstructured materials for a number of applications. Prominent applications range from advanced electronics to miniaturized electrochemical energy storage devices (EESDs). Herein, we present a comprehensive and critical review of the recent developments in design and microfabrication of 2D-driven microscale electrodes for three-dimensional (3D)-printed micro-supercapacitors and micro-batteries. Firstly, we systematically discuss the advantages and disadvantages associated with various microfabrication techniques such as stereolithography, fused deposition modeling, inkjet printing, and direct ink writing. Next, key parameters disclosing the relationship between the characteristics of 2D-based materials and extrusion-driven 3D printing process for the development of versatile and sustainable EESDs are highlighted. 2D materials utilized for the construction of microelectrodes for supercapacitors (e.g., electric double layer capacitors (EDLCs), pseudocapacitors, and hybrid capacitors) and batteries (e.g., Li-based systems and next-generation systems, e.g., sodium-ion batteries and zinc-ion batteries) along with their prominent electrochemical contributions in relation to obtained 3D-printed architectures are discussed in detail. To promote the development of 2D materials-driven high-performance microscale EESDs, the relevant challenges and future research opportunities are also addressed.

A novel fluorescence probe for ultrafast detection of SO2 derivatives/biogenic amines and its multi-application: Detecting food and fish freshness, fluorescent dye and bioimaging

In this study, we have effectively prepared a novel fluorescent probe named HDXM based on benzopyran derivatives for the ultrafast detection (within 3 s) of SO2 derivatives or biogenic amines. HDXM showed a noticeable color change after the addition of SO2 derivatives (from purple to colorless) or biogenic amines (from purple to blue), indicating that HDXM can identify two analytes with the naked eye. It is worth noting that HDXM can be used to detect SO2 derivatives in actual sugar samples, and to image HSO3−/SO32− in living cells. More importantly, sensing labels (HDXM-loaded filter paper or agarose hydrogel) enable real-time visual monitoring of salmon freshness through colorimetric and fluorescence dual channels. Compared with the Chinese national standard method, the sensing label is an effective tool for evaluating the freshness of fish. Benefiting from its excellent solubility and fluorescence performance, HDXM can be used as a versatile fluorescent material in various applications, including flexible films, glass coatings, impregnating dyes, printing, and fingerprint ink. HDXM is expected to be a promising and valuable multifunctional tool for food safety and fluorescent materials.

Closed-loop recycling of polypropylene: A case study on mechanical recycling of separately collected yogurt cups in Austria

Yogurt cups with their recognizable design are made from plastics that are approved for food contact. The materials used have an interesting property profile. Therefore, these products represent a promising waste fraction for plastics recycling. In this study, yogurt cups were pre-sorted by consumers and further hand-sorted. A 2:1 ratio of polypropylene (PP) cups to polystyrene cups was found. In terms of decorations, cups with printing inks dominated. Two thirds of the PP cups were produced by thermoforming and one third by injection molding. Compositional analysis of the recycled PP showed no significant contamination other than residual dyes. Material characterization exhibited that both processing and application-oriented properties can compete with virgin material. To demonstrate a closed-loop, the recycled PP was used to produce thermoformed cups with exceptional properties. This study shows the positive effect of closed-loop recycling and points out potential waste fractions that can be used in the future.

Naturally Crosslinked Biocompatible Carbonaceous Liquid Metal Aqueous Ink Printing Wearable Electronics for Multi-Sensing and Energy Harvesting

HighlightsNaturally crosslinked carbonaceous liquid metal aqueous printable ink mediated by biopolymers.E-textile with conductivity, stability, wearability, and aesthetic characteristics.Multi-applications in health monitoring, pressure sensing, and energy harvesting.

The importance of mechanical and biological cues of tympanic membrane grafts to ensure optimal regeneration

Chronic suppurative otitis media (CSOM) is often associated with permanent tympanic membrane (TM) perforation and conductive hearing loss. The current clinical gold standard, using autografts and allografts, suffers from several drawbacks. Artificial replacement materials can help to overcome these drawbacks. Therefore, scaffolds fabricated through digital light processing (DLP) were herein created to support TM regeneration. Various UV-curable printing inks, including gelatin methacryloyl (GelMA), gelatin-norbornene-norbornene (GelNBNB) (crosslinked with thiolated gelatin (GelSH)) and alkene-functionalized poly-ε-caprolactone (E-PCL) (crosslinked with pentaerythritol tetrakis(3-mercaptopropionate) (PETA4SH)) were optimized regarding photo-initiator (PI) and photo-absorber (PA) concentrations through viscosity characterization, photo-rheology and the establishment of working curves for DLP. Our material platform enabled the development of constructs with a range of mechanical properties (plateau storage modulus varying between 15 and 119 kPa). Excellent network connectivity for the GelNBNB and E-PCL constructs was demonstrated (gel fractions >95 %) whereas a post-crosslinking step was required for the GelMA constructs. All samples showed excellent biocompatibility (viability >93 % and metabolic activity >88 %). Finally, in vivo and ex vivo assessments, including histology, vibration and deformation responses measured through laser doppler vibrometry and digital image correlation respectively, were performed to investigate the effects of the scaffolds on the anatomical and physiological regeneration of acute TM perforations in rabbits. The data showed that the most efficient healing with the best functional quality was obtained when both mechanical (obtained with the PCL-based resin) and biological (obtained with the gelatin-based resins) material properties were taken into account.