Inks For 3D Printing Research Articles

Extrusion-Based 3D Printing of Pharmaceuticals—Evaluating Polymer (Sodium Alginate, HPC, HPMC)-Based Ink’s Suitability by Investigating Rheology

Three-dimensional printing is promising in the pharmaceutical industry for personalized medicine, on-demand production, tailored drug loading, etc. Pressure-assisted microsyringe (PAM) printing is popular due to its low cost, simple operation, and compatibility with heat-sensitive drugs but is limited by ink formulations lacking the essential characteristics, impacting their performance. This study evaluates inks based on sodium alginate (SA), hydroxypropyl cellulose (HPC H), and hydroxypropyl methylcellulose (HPMC K100 and K4) for PAM 3D printing by analyzing their rheology. The formulations included the model drug Fenofibrate, functional excipients (e.g., mannitol, polyethylene glycol, etc.), and water or water–ethanol mixtures. Pills and thin films as an oral dosage were printed using a 410 μm nozzle, a 10 mm/s speed, a 50% infill density, and a 60 kPa pressure. Among the various formulated inks, only the ink containing 0.8% SA achieved successful prints with the desired shape fidelity, linked to its rheological properties, which were assessed using flow, amplitude sweep, and thixotropy tests. This study concludes that (i) an ink’s rheological properties—viscosity, shear thinning, viscoelasticity, modulus, flow point, recovery, etc.—have to be considered to determine whether it will print well; (ii) printability is independent of the dosage form; and (iii) the optimal inks are viscoelastic solids with specific rheological traits. This research provides insights for developing polymer-based inks for effective PAM 3D printing in pharmaceuticals.

Concentrated Pre-Vulcanized Natural Rubber Latex Without Additives for Fabricating High Mechanical Performance Rubber Specimens via Direct Ink Write 3D Printing

Direct ink writing (DIW) is an economical, straightforward, and relatively energy-efficient 3D printing technique that has been used in various domains. However, the utilization of rubber latex for DIW remains limited due to its high fluidity and inadequate support, which makes it challenging to meet the required ink rheological characteristics for DIW. In this study, a concentrated pre-vulcanized natural rubber latex (CPNRL) ink with a high solid content of 73% without additives is developed for DIW 3D printing. The CPNRL ink is concentrated using superabsorbent polymer (SAP) beads, which demonstrates good colloidal stability, favorable rheological properties, and superior printability. The impact of printing angles on the mechanical properties of the rubber specimens based on the CPNRL-73 ink is explored in detail, wherein the tensile strength of the specimen printed at a 90° angle reaches an impressive 26 MPa and a strain of approximately 800%, which surpasses the majority of 3D-printed rubber latex specimens. Additionally, the CPNRL ink can be used to print a wide range of intricate shapes, demonstrating its advantages in excellent formability. The preparation of 3D printable ink using the absorption method will expand the application of elastomers in fields such as customized flexible sensing and personalized rubber products.

Dual effects of exogenous ferulic acid bound in rice starch as 3D printable food ink: Structural fluidity and antimicrobial activity.

Starch-ferulic acid (FA) composites have been developed for medical and food fields, while little focus is caused on their use in functional products by 3D printing. In this work, dynamic high-pressure microfluidization was employed to treat starch at various concentrations, for preparing modified starch-FA composites. The high-performance liquid chromatography results showed that an increased starch concentration was conducive to a high yield of composite with enhanced binding of FA. Compared with pure starch and starch-FA mixture gel, the starch-FA composite gel possessed lower viscosity, with a dramatically reduced extrusion pressure in the 3D printing test. Furthermore, antimicrobial activity tests indicated that the starch-FA composite gel can inhibit the growth of microorganism for achieving a long storage period. Overall, we provide a biomaterial of starch-FA composite that can serve as both a 3D printing food ink and an edible, printable, active, and lightweight packaging ink.

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

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

Unveiling the potential of bean proteins: Extraction methods, functional and structural properties, modification techniques, physiological benefits, and diverse food applications.

Bean proteins, known for their sustainability, versatility, and high nutritional value, represent a valuable yet underutilized resource, receiving less industrial attention compared to soy and pea proteins. This review examines the structural and molecular characteristics, functional properties, amino acid composition, nutritional value, antinutritional factors, and digestibility of bean proteins. Their applications in various food systems, including baked goods, juice and milk substitutes, meat alternatives, edible coatings, and 3D printing inks, are discussed. The physiological benefits of bean proteins, such as antidiabetic, cardioprotective, antioxidant, and neuroprotective effects, are also presented, highlighting their potential for promoting well-being. Our review emphasizes the diversity of bean proteins and highlights ultrasound as the most effective extraction method among available techniques. Beyond their physiological benefits, bean proteins significantly enhance the structural, technological, and nutritional properties of food systems. The functionality can be further improved through various modification techniques, thereby expanding their applicability in the food industry. While studies have explored the impact of bean protein structure on their nutritional and functional properties, further research is needed to investigate advanced modification techniques and the structure-function relationship. This will enhance the utilization of bean proteins in innovative and sustainable food applications.

Enhanced 3D printing performance of soybean protein isolate nanoparticle-based O/W Pickering emulsion gels by incorporating different polysaccharides.

This work investigated the feasibility of employing soybean protein isolate nanoparticles (SPINPs) as emulsifiers and polysaccharides with different charge properties as thickeners to develop oil-in-water (O/W) Pickering emulsion gels 3D printing inks. The impact of non-covalent interactions between SPINPs and various polysaccharides on the microstructure, rheological properties, and 3D printability of emulsion gels was investigated at pH3 and pH7, respectively. Results showed that Locust bean gum (LBG) and Konjac gum (KG) stabilized emulsion gels mainly by increasing the viscosity of the aqueous phase. Chitosan (CS) and xanthan gum (XG) improved the system's viscosity while combining with SPINPs via electrostatic interactions. Small amplitude oscillatory shear and large amplitude oscillatory shear test results showed the highest recovery rate (97.45%) and gel strength of 7-XG, exhibiting good potential for 3D printing. The Lissajous curves revealed the weakest gel structure and larger dimensional printing deviation (27.57%) of 3-XG. The 3D-printed products of LBG and KG emulsion gels demonstrated smooth and slightly flawed surface texture. The print deformation rate of CS emulsion gels was <5.5%, which was most suitable for developing 3D printing inks. This study offers valuable insights for creating and designing protein-polysaccharide-based 3D printing inks.

Tricalcium phosphate-based capillary suspensions as inks for 3D printing of porous scaffolds

Tricalcium phosphate-based capillary suspensions as inks for 3D printing of porous scaffolds

Pinch-off dynamics of emulsion filaments before and after polymerization of the internal phase.

The capillary break-up of complex fluid filaments occurs in many scientific and industrial applications, particularly in bio-printing where both liquid and polymerized droplets exist in the fluid. The simultaneous presence of fluid and solid particles within a carrier fluid and their interactions lead to deviations in the filament break-up from the well-established capillary breakup dynamics of single-phase liquids. To examine the significance of the dispersed phase and the internal interactions between liquid droplets and solid particles, we prepare emulsions through photopolymerization and conduct experimental investigations into the pinch-off dynamics of fluid filaments, focusing on the impact of varying concentrations of liquid droplets (before polymerization) and polymerized droplets. Despite the increase in bulk viscosity due to the presence of polymerized droplets in the fluid and their aggregation, the results show that polymerization significantly reduces the length of the fluid filament before breakup, thus shortening the duration of pinch-off. We investigate two categories of complex fluids, characterized by their droplet sizes: (i) sub-micrometer droplets and (ii) droplets with an average diameter of 50 micrometers. In emulsions containing sub-micrometer droplets, the individual droplet contributions remain undetectable during capillary breakup, and the measured pinch-off dynamics predominantly reflect the bulk shear viscosity or viscoelasticity of the system. This is due to the droplet sizes falling below our imaging resolution. In contrast, emulsions with larger polymerized droplets exhibit behavior analogous to single-phase carrier fluids: once the filament's length equals the droplet diameter, the droplets are expelled. Concurrently, larger liquid droplets are deformed and elongated along the flow direction. Our study highlights the effect of mixing liquid and polymerized droplets on the capillary breakup dynamics of fluid filaments, providing insights to formulate 3D printing inks.

A Dual Binder Concept for 3D Printing Ink: Triggered Polymerization for Rapid Stiffening and Carbonation for Final Strength

A Dual Binder Concept for 3D Printing Ink: Triggered Polymerization for Rapid Stiffening and Carbonation for Final Strength

Nanoliposome functionalized colloidal GelMA inks for 3D printing of scaffolds with multiscale porosity

Bioprinting has enabled the creation of intricate scaffolds that replicate the physical, chemical, and structural characteristics of natural tissues. Recently, hydrogels have been used to fabricate such scaffolds for several biomedical applications and tissue engineering. However, the small pore size of conventional hydrogels impedes cellular migration into and remodeling of scaffolds, diminishing their regenerative potential. Porous scaffolds have been utilized for their improved diffusion of nutrients, dissolved oxygen, and waste products. However, traditional methods of generating porous structures require multiple processing steps, making them incompatible with bioprinting. Recently, we developed a method to generate multi-scale porous structures by foaming hydrogel precursors prior to printing to form colloidal bioinks. Here, to further improve the biological, mechanical, and physical properties, we functionalize colloidal bioinks with nanoliposomes (NLs), one of the most promising methods for bioactive delivery. We assess the impact of the concentration of NL on the characteristics of bioinks made from gelatin methacryloyl (GelMA) and their resulting scaffolds. Anionic liposomes made from rapeseed lecithin of 110 nm were synthesized and found to be stable over several weeks. Increasing concentrations of NL decreased the zeta potential and increased the viscosity of foamed bioinks, improving their rheological properties for printing. Furthermore, the incorporation of NL allowed for precise adjustment of the macropore size and bulk mechanical properties without any chemical interaction or impact on photocrosslinking. The nanofunctionalized foam bioinks, composed exclusively of natural components, demonstrated significant antioxidant activity and were printed into multilayered scaffolds with high printability. The foam-embedded NL showed remarkable biocompatibility with myoblasts, and cell-laden bioinks were able to be successfully bioprinted. Due to their high biocompatibility, tunable mechanical properties, printability, and antioxidant behavior, the nanofunctionalized porous scaffolds have promise for a variety of biomedical applications, including those that require precise delivery of therapeutic substances and tissue engineering.

A low-cost, open-source cylindrical Couette rheometer

Rheology describes the flow of fluids from food and plastics, to coatings, adhesives, and 3D printing inks, and is commonly denoted by viscosity alone as a simplification. While viscometers adequately probe Newtonian (constant) viscosity, most fluids have complex viscosity, requiring tests over multiple shear rates, and transient measurements. As a result, rheometers are typically large, expensive, and require additional infrastructure (e.g., gas lines), rendering them inaccessible for regular use by many individuals, small organizations, and educators. Here, we introduce a low-cost (under USD$200 bill of materials) Open Source Rheometer (OSR), constructed entirely from thermoplastic 3D printed components and off-the-shelf electromechanical components. A sample fluid rests in a cup while a micro stepping motor rotates a tool inside the cup, applying strain-controlled shear flow. A loadcell measures reaction torque exerted on the cup, and viscosity is calculated. To establish the measurement range, the viscosity of four Newtonian samples of 0.1–10 Pa.s were measured with the OSR and compared to benchmark values from a laboratory rheometer, showing under 23% error. Building on this, flow curves of three complex fluids – a microgel (hand sanitizer), foam (Gillette), and biopolymer solution (1% Xanthan Gum) – were measured with a similar error range. Stress relaxation, a transient test, was demonstrated on the biopolymer solution to extract the nonlinear damping function. We finally include detailed exposition of measurement windows, sources of error, and future design suggestions. The OSR cost is ∼1/25th that of commercially available devices with comparable minimum torque (200 µN.m), and provides a fully open-source platform for further innovation in customized rheometry.

Synergistic stabilization of oil-in-water emulsion gels by pea protein isolate and cellulose nanocrystals: Effects of pH and application to 3D printing.

In this study, pea protein isolate (PPI) and cellulose nanocrystals (CNC) were used to prepare oil-in-water emulsions, and the effects of pH and the oil content on the properties of the emulsions were investigated. The microstructural analysis revealed that PPI and CNC formed complexes by electrostatic attraction at pH3.0 and 4.5, which assembled a dense interfacial layer around the oil droplets, improving emulsification performance. Moreover, the emulsions at these pH conditions exhibited semi-solid gel properties when the oil content was increased to 75wt%, with better viscoelasticity compared to pH8.0 and high thixotropic recovery rates in rheological experiments. Printing of flat stacked models with these high internal phase emulsions had a deformation rate of around 5%, indicating desirable shear resistance and fidelity. These findings would offer valuable insights for developing fat substitutes and their application as edible inks for 3D printing.

Octenyl succinic anhydride starch enhanced 3D printability of corn starch-based emulsion-filled gels incorporating egg yolk

This work investigated the effect of octenyl succinic anhydride starch (OSAS) on the 3D printing performance of corn starch-based emulsion-filled gels containing egg yolk. The influence of OSA-S concentration on emulsion droplet size, ζ-potential and stability, as well as the printing performance, rheological properties and microstructure of gel were discussed. The results indicated that the addition of OSA-S significantly improved the accuracy of the printed objects, with the best accuracy of the models printed using OSA-1.6 and OSA-2.0 inks. Emulsion tests showed that increasing the OSA-S content reduced the droplet size, increased its ζ-potential, and enhanced the stability of the emulsion. Rheological analyses showed that the energy storage modulus, loss modulus, and apparent viscosity of the gels were slightly enhanced with increasing OSA-S content. Microstructural analysis showed that OSA-S increased the density of the gel microstructural network. In addition, the addition of OSA-S enhanced the thermal stability of the gels and facilitated the transition of water molecule states from free water to bound water. The melting temperature of the gel gradually increased from 135.72 °C to 147.52 °C with the increase of OSA content. This study aims to develop promising 3D printing ink to facilitate its industrial applications.

Film forming properties of 3D printed polysaccharide based gels and development of CO2 monitoring labels

Polyvinyl alcohol (PVA) has good compatibility with polysaccharides and is suitable for 3D printing inks for preparing food packaging films or smart labels. In this work, the influences of different concentrations of PVA on the 3D printability and film-forming performance of six polysaccharide-based inks were investigated. PVA formed a strong cross-linked network with sodium alginate (SA) and carboxymethyl cellulose (CMC), which enhanced the 3D printability of the gel, and the addition of 7 % PVA increased the printing accuracy of SA by 20.83 times. PVA also facilitated the smooth extrusion of potato starch (PS), pectin (PE), konjac glucomannan (KGM), and xanthan gum (XG) inks in the printing operation and improved their flowability. The surface of 3D printed PVA- polysaccharide film had tiny print texture, no obvious roughness or graininess, smooth surface, soft texture and good shape. However, cracks and wrinkles were found on the surface of the PVA-PS membrane, which were likely related to inappropriate ratios and uneven shrinkage. FTIR and XRD analysis showed that PVA had excellent compatibility with polysaccharides and was fully distributed within the film. A 3 % PVA addition was found to be optimal, as the polysaccharide films exhibited appropriate hydrophilicity, mechanical strength, and flexibility. The color of polysaccharide-based labels containing bromothymol blue (BTB) and methyl red (MR) prepared with 3 % PVA content changed with the change of CO2 concentration. 3D printed labels were successfully used to monitor the changes of CO2 concentration in tomato packaging during storage. This research extends the applicability of 3D-printed smart labels for real-time monitoring environmental conditions of fruits and vegetables storage, particularly CO2 concentration.

Enhancing 3D printing accuracy of cassava starch gel through temperature-controlled freezing

Starch is an important renewable resource, however, the performance of 3D printing inks prepared from it requires improvement. This study revealed the effects of different freezing temperatures (25 °C, 4 °C, 0 °C, −20 °C, −40 °C, −80 °C) on the 3D printing accuracy of cassava starch (CS) gels in terms of starch gel properties (rheological properties, moisture distribution, submicroscopic structure) and multiscale structure (molecular size, chain length distribution, short-range ordered structure). As the freezing temperature decreased, the molecular size and the amylose (Am) content in CS gel were increased, particularly for short Am chains (X∼100–1000). These resulted in a greater orderly structure of the starch, enhancing the elastic modulus of the gel. Moreover, the lower the freezing temperature, the higher mobility of water molecules within the gel matrix after thawed, which in turn caused the reduction of gel viscosity and facilitated the smooth squeezing of the gel. After freeze-thawing at cryogenic temperatures, the above changes in CS gel properties improved the stiffness and support performance of the gel structure, thereby enhancing the 3D printing precision. This study provides insights into the development of 3D printing technology for starchy food materials, emphasizing its potential to transform the customization of starch-based food processing by enabling customized food products, enhancing texture, and offering consumers personalized food choices and improved sensory experiences.

3D printed collagen scaffold for heart valve repair

Three-dimensional (3D) bioprinting has emerged as a promising approach for the development of functional tissues and organs, including the heart valves. In this study, we investigated the interaction of 3D printed collagen scaffolds with H9c2(2–1) and NIH/3T3 cells to improve heart-valve repair strategies. Type I collagen was extracted from rat tails, characterized using SDS-PAGE and Raman spectroscopy, and used as a biomaterial ink for 3D printing. The rheological properties were evaluated. The FRESH technique was used to support the printed construct. In vitro assessments were performed to determine the cell viability and distribution within the scaffold. These results demonstrated the successful extraction and characterization of Type I collagen, which exhibited suitable rheological properties for 3D bioprinting. The printed collagen scaffolds supported the growth and distribution of H9c2(2–1) and NIH/3T3 cells, indicating their potential application in heart valve repair. This study highlights the importance of collagen as a biomaterial in 3D bioprinting and provides insights into the development of advanced strategies for heart valve repair.

Optimizing Tilapia-based surimi ink for 3D printing: Enhancing physicochemical properties and printability with Ulva powder

The elderly face malnutrition and dysphagia. 3D printing with high-protein surimi offers an innovative way to customize nutrition and texture of foods for the elderly. This study explored whether tilapia-based surimi ink (TBSI) with Ulva powder (UP, 0–3 %) could improve physicochemical properties and printability as an alternative to traditional pollock-based surimi ink (PBSI). TBSI showed a more uniform microstructure, greater water-holding capacity (WHC), and better printability with consistent extrusion than PBSI. Adding UP to TBSI promoted cross-linking and enhanced microstructure and WHC. Rheological analysis revealed that all inks exhibited shear-thinning behavior. UP increased complex viscosity, storage modulus, and loss modulus. Notably, UP above 2 % improved protein matrix uniformity, structural integrity, and printability, as confirmed by FT-IR and 3D printing tests. The hardness of steamed TBSI fish cake increased when infill density increased. This study highlights the potential of TBSI with UP for 3D printing to prepare personalized and elderly-friendly food.

Ductile (Ag,Cu)2(S,Se,Te)-based auxetic metamaterials for sustainable thermoelectric power generation

Sustainable energy solution has resulted in significant interest in thermoelectric power generation, converting waste heat into electricity. However, the practical application of thermoelectric generators has been hindered by issues with their adaptability to arbitrary heat sources and durability in an operational environment. Here, we propose deformable auxetic thermoelectric metamaterials composed of high-entropy (Ag,Cu)2(S,Se,Te) ductile alloys, realized using finite element modelling and three-dimensional (3D) printing. We design a re-entrant auxetic structure with a negative Poisson’s ratio to maximize the mechanical deformability and develop an (Ag,Cu)2(S,Se,Te) particle-based colloidal 3D printable ink, tailored with Te microparticles. The 3D-printed (Ag,Cu)2(S,Se,Te) alloy exhibit a ZT value of 1.15 coupled with high compressive strength (208 MPa) and fracture strain (17.5 %). The fabricated auxetic metamaterials exhibit excellent vibrational stability and adaptability to diverse curved surfaces, realizing efficient power generation on a synclastic curved heat source. Our approach offers a method to design durable and efficient heat recovery devices.

Development of beetroot powder-enriched inks for 3D food printing based on hydrogel/oleogel bigels

3D printing with bigel inks exhibits substantial potential for food structuring and nutritional innovation, particularly through the enrichment of foods with vegetables rich in health-promoting bioactive compounds. This study focuses on the preparation of bigels incorporating beetroot powder. Hydrogels based on xanthan gum, carrageenan, and guar gum were used in combination with monoglyceride oleogels to formulate suitable inks for extrusion-based 3D food printing. This study investigated the effects of hydrogel type, vegetable powder content, and hydrogel:oleogel mass ratio on the microstructure, rheological properties, and extrusion behavior of the bigels. Furthermore, the printability of the selected formulations was evaluated. The inclusion of beetroot powder enhanced the structure and mechanical strength of all the hydrogels. Bigels prepared with an 80:20 mass ratio yielded homogeneous materials for all three hydrogelators. They exhibited maximum storage modulus values of 1.1E4, 7.8E3, and 3.3E3 Pa for guar gum, carrageenan, and xanthan gum, respectively. Moreover, these bigels partially recovered of their initial structure after the application of high strain and demonstrated appropriate flowability for extrusion through 1.2 and 2 mm 3D printer nozzles. Successful printing of 2D (grid) and 3D (cube) structures was achieved using guar gum-based bigels, followed by carrageenan-based counterparts, which displayed superior dimensional accuracy, structural integrity, enhanced line resolution, and minimal printing errors and deformations. These findings provide valuable insights and lay the groundwork for developing more complex and functional food structures.

A novel route to 3D printable protein-based HIPEs developed with shiitake oil

Tuning protein-based Pickering high internal phase emulsions (HIPEs) into 3D printing inks is promising in the food fields. Currently, the correlation between the changes in oil phase composition and the regulation of protein-based HIPEs 3D printing performance is still unclear. In this study, spiking the shiitake oil (ranging from 0 to 60 %) into the soybean oil phase of HIPEs can enhance their rheological properties and induce the formation of 3D printable HIPEs. The rheological tests showed that the yield stress and viscosity of the HIPEs respectively increased from 81.8 ± 4.84 Pa to 309 ± 16.3 Pa and from 409–1.74 Pa.s to 1762–2.93 Pa.s with increasing the shiitake oil concentration (0 % to 60 %) in the oil phase. In this study, the spontaneous interaction between phenolic compounds in shiitake oil and interfacial casein promoted the aggregation of protein, which led to the formation of casein cross-linking network in emulsion droplets, thus realizing the self-supporting and printing fidelity required for 3D printing. These findings provide a new perspective for enhancing the 3D printing properties of protein-based HIPEs.