Direct ink writing, often abbreviated as DIW, belongs to the broader family of additive manufacturing technologies that build objects layer by layer directly from a digital model. Unlike laser-based powder bed fusion or vat photopolymerization, DIW relies on a simple but demanding principle: a viscous paste, called the ink, is pushed through a fine nozzle and deposited along a programmed toolpath. The trick is that the ink must flow easily under the shear stress of extrusion, yet instantly stiffen once it leaves the nozzle so that it holds its shape and supports the layers printed on top of it. Achieving that dual behavior is the central challenge of the entire technique, and it is governed by the field of rheology, the science of how materials deform and flow.

The review devotes considerable attention to the composition of ceramic inks, which typically combine ceramic powder with a liquid medium, binders, dispersants, and various additives. The ceramic powder provides the final material properties, while the liquid carrier determines whether the ink is water-based or solvent-based. Dispersants keep the fine particles from clumping together, a critical concern because agglomerates can clog the nozzle and create defects in the printed part. Binders give the freshly extruded filament its green strength, allowing it to survive handling before the part is fired. The authors explain that the selection of each component is a balancing act: too much binder and the part will shrink or crack during burnout, too little and the printed structure collapses under its own weight.

At the heart of ink design lies a rheological profile that researchers describe as shear-thinning behavior with a yield stress. In practical terms, the ink behaves like a solid at rest, but when forced through the nozzle it temporarily liquefies. Models such as the Herschel-Bulkley equation are commonly used to capture this behavior, relating the applied stress to the resulting flow rate. Solid loading, meaning the fraction of the ink volume occupied by ceramic particles, is another decisive parameter. Higher solid loading produces denser, stronger parts after sintering and reduces shrinkage, but it also raises viscosity and makes extrusion harder. Studies on alumina, zirconia, and titania inks cited in the review show how researchers tune particle size distributions and additive chemistry to push solid loading as high as possible without sacrificing printability.

The mechanics of the printing process itself come in several variants. Pneumatic extrusion uses pressurized air to drive the ink, offering simple control but limited precision with very viscous pastes. Piston-driven systems push the material mechanically, providing more consistent volumetric flow, while screw-driven extruders can handle extremely high-viscosity feedstocks and even enable co-extrusion of multiple materials. Nozzle geometry, printing speed, and layer height all influence the final geometry, and the review highlights how dimensional accuracy and surface roughness depend on carefully matching these parameters to the ink’s flow characteristics. More advanced approaches, such as embedded printing, in which the ink is deposited into a supporting gel bath, allow genuinely freeform structures with overhangs that would otherwise sag or collapse.

Once printing is complete, the part is still a fragile green body held together by binder. It must first undergo debinding, a careful thermal or solvent treatment that removes the organic components without causing cracks, and then sintering at high temperature to densify the ceramic. The review emphasizes that these post-processing steps are just as important as printing itself: rapid heating during binder burnout can leave behind carbon residues or trigger catastrophic failure, while sintering conditions determine the final microstructure, grain size, and porosity. Emerging techniques such as flash sintering and rapid sintering are being explored to shorten these energy-intensive stages and bring printed ceramics closer to industrial throughput.

The range of ceramics now being printed by DIW is remarkably broad. Oxide ceramics such as alumina and zirconia dominate structural and biomedical applications, with zirconia-toughened alumina pastes yielding dense, high-strength components. Non-oxide ceramics, including silicon carbide, boron carbide, silicon nitride, and ultra-high temperature ceramics such as zirconium diboride, are being printed for demanding applications ranging from armor to aerospace, often using preceramic polymers as ink precursors that convert to ceramic during pyrolysis. Bioceramics such as hydroxyapatite, beta-tricalcium phosphate, and bioactive glasses are printed into porous bone scaffolds whose interconnected channels guide tissue regeneration, and several studies report promising in vivo bone responses to DIW-fabricated hydroxyapatite implants.

Perhaps the most exciting frontier is ceramic matrix composites and architectured materials. By incorporating continuous carbon fibers, ceramic whiskers, or graphene-based additives into the ink, researchers have produced composites with dramatically improved fracture toughness, a long-standing weakness of monolithic ceramics. Multi-material and core-shell printing takes this further, allowing gradients in composition that mimic the elegant microstructures of natural materials such as nacre, in which layered architecture turns brittle constituents into resilient structures. Printed piezoelectric ceramics, wave-transparent silica fiber composites, catalyst supports with hierarchical porosity, and even refractory waste-derived parts demonstrate how the technique spans energy, electronics, environmental, and structural applications.

The review is candid about the obstacles that remain. Nozzle clogging, especially with fiber-reinforced inks, continues to plague long prints, and the layer-by-layer nature of extrusion leaves anisotropic weaknesses at interfaces between deposited strands. Shrinkage during drying and sintering complicates dimensional control, and the slow deposition rates of fine nozzles limit the size of parts that can be produced economically. Real-time process monitoring, pressure-based feedback, and machine-vision defect detection are emerging as tools to address reliability, while in situ curing and novel binder chemistries aim to strengthen green parts before firing.

What emerges from this comprehensive survey is a field in rapid maturation. Direct ink writing has moved from laboratory demonstrations of periodic lattice structures two decades ago to functional ceramic components with genuine engineering relevance, from load-bearing dental prostheses to hydrogen-production catalyst supports. The authors argue that the path forward lies in systematic ink design, deeper structure-property correlations, and smarter process control, all of which could finally make complex-shaped ceramics as printable and dependable as the polymers and metals that currently dominate the 3D printing landscape. If that happens, the materials that already protect spacecraft and power jet engines may soon be shaped as freely as any plastic filament.

Subject of Research: Direct ink writing as an additive manufacturing technique for ceramics and ceramic composites

Article Title: Review: 3D printing of ceramics using direct ink writing

Article References: Kumar, A., Maji, B., & Mallik, M. (2026). Review: 3D printing of ceramics using direct ink writing. Journal of Materials Science. https://doi.org/10.1007/s10853-026-13774-w

Image Credits: AI Generated

DOI: 10.1007/s10853-026-13774-w

Keywords: direct ink writing, ceramics, 3D printing, additive manufacturing, rheology, ceramic inks, sintering, bioceramics, ceramic matrix composites, extrusion, porosity, preceramic polymers

The research team, led by Mursalin Sajib and Lutz Grossmann at the University of Massachusetts Amherst together with USDA collaborators including Raymond Glahn and Karen Cichy, took five pulse flours through an identical low-moisture extrusion process: a Manteca-type yellow bean called USDA Yellowjacket, a commercial navy bean mix, California Blackeye 77 cowpea, and commercially purchased chickpea and red lentil flours. The goal was twofold. First, to test whether unrefined whole-pulse flours, with all their inherent chemical complexity, could be reliably extruded into expanded snacks. Second, to determine whether the type of pulse and the type of processing changed how much iron the human intestine could actually take up.

On the processing side, the answer was a qualified yes. Using a co-rotating twin-screw extruder with a barrel temperature profile reaching 160 degrees Celsius and a feed moisture of 20 percent, all five flours produced puffed extrudates, but with strikingly different properties. Specific mechanical energy and die pressure varied significantly across flours, reflecting differences in starch composition and lipid content. Chickpea flour, with roughly six percent fat acting as an internal lubricant, expanded the least and produced the hardest puffs, with an expansion ratio of only 2.44 and a hardness of nearly 25 newtons. Red lentil, with the lowest fiber content, expanded the most at 6.44 and yielded the softest product. Yellow and navy bean puffs landed in a favorable middle ground, with expansion ratios above 4.3, hardness values around 2.2 to 2.5 newtons, and relatively low water activity, performing comparably to red lentil, a pulse already established in commercial puffed snacks.

The nutritional story proved even more interesting. Total iron concentrations were highest in the yellow bean, navy bean and cowpea flours, and processing into porridge or puffs barely changed them. But iron content alone told almost nothing about bioavailability. When the researchers ran each product through an in vitro digestion followed by the Caco-2 cell bioassay, a validated model in which intestinal cells respond to iron uptake by producing ferritin, the differences were dramatic. Yellow bean porridges and puffs produced ferritin responses of roughly 30 nanograms per milligram of cell protein, far above every other pulse product and approaching, though not matching, the 44 to 49 nanograms per milligram seen with cooked ground beef and a plant-based burger reference. Navy bean products came second. Cowpea products, despite their high iron content, performed worst of all.

The explanation lay in the chemistry of inhibitors rather than the abundance of iron. Phytic acid, the classic antinutrient that chelates ferric iron in the gut, was reduced by both boiling and extrusion, with puffs showing greater reductions than porridges. All puffed products achieved phytate-to-iron molar ratios between 6 and 9, below the threshold of 10 associated with meaningful inhibition. Lectin activity, a safety concern in undercooked beans, was undetectable in all porridges and in most puffs, confirming that both processing routes rendered the products safe. Yet these improvements applied broadly and could not explain why yellow bean so clearly outperformed the rest.

The decisive factor turned out to be flavonoids, the polyphenols concentrated in bean seed coats. Flavonoids split into two camps with opposite effects on iron uptake. Enhancers such as kaempferol and its glycosides, along with epicatechin, keep iron soluble and available for transport. Inhibitors, particularly galloylated compounds like myricetin, delphinidin and gallocatechin derivatives, form stable, non-transportable iron complexes. The dose-response is brutally asymmetric: previous work has shown that adding just 10 percent myricetin to an epicatechin mixture cuts iron bioavailability by about 65 percent. Yellow bean flour was rich in kaempferol and its glucosides, with over 770 nanomoles per gram of kaempferol 3-glucoside, while containing essentially no inhibitory flavonoids. Cowpea, by contrast, carried a full payload of galloylated inhibitors, including myricetin 3-glucoside, delphinidin 3-glucoside and petunidin 3-glucoside, which persisted at elevated levels even after processing.

Statistical analysis confirmed the hierarchy of effects. Spearman correlation and principal component analysis converged on the same conclusion: cellular iron uptake correlated negatively with summed inhibitory flavonoids (rho of minus 0.75), zinc (minus 0.72) and phytic acid (minus 0.62), while total iron showed no significant correlation at all (rho of 0.12). The summed enhancer flavonoids were likewise uncorrelated with uptake, suggesting that their benefit is realized only when inhibitors are nearly absent, as they are in yellow bean. Extrusion itself provided a modest additional boost over porridge processing, most visibly for chickpea and red lentil, likely through disruption of cotyledon cell walls that otherwise shield iron from digestive enzymes.

The practical implications are considerable. A standard snack serving of 30 to 50 grams of yellow bean puffs could make a nutritionally relevant contribution to daily iron intake, which ranges from 8 milligrams for adult men to 27 milligrams during pregnancy, assuming the in vitro findings translate to human absorption. Beyond standalone snacks, the authors calculate that incorporating roughly 35 percent yellow bean flour into plant-based meat alternatives would deliver iron comparable to lean meat on a weight-for-weight basis, while also contributing about 17 percent protein and 20 percent dietary fiber. Because the flour is unrefined, no fractionation side streams are generated, aligning the approach with sustainability goals. The Manteca yellow bean market class has already been formulated into a pasta with higher iron bioavailability than enriched wheat or commercial chickpea and lentil pastas, though the authors caution that not all yellow bean market classes share these favorable traits.

Important caveats remain. The Caco-2 model measures cellular iron uptake rather than transepithelial transport or true fractional absorption in humans, and whole-meal context, iron status of the consumer, and unmeasured matrix components all influence real-world outcomes. The extrusion trials were limited to two independent replicates per flour, and the phenolic profiling was targeted rather than untargeted. The authors call for animal and human intervention studies, broader compositional screening, and testing of yellow bean ingredients within complete meals. Still, the central message stands: when it comes to plant-based iron, the company iron keeps inside the food matrix matters more than how much of it is there, and breeding and processing strategies that minimize inhibitory flavonoids while preserving enhancers offer a scalable, evidence-based route to better iron nutrition.

Subject of Research: Iron bioavailability in extruded whole-pulse snack foods

Article Title: Matrix-controlled iron bioavailability in unrefined whole-pulse low-moisture extrudates

Article References: Sajib, M., Wiesinger, J., Xie, H., Cichy, K., Hooper, S., Howe, K., Glahn, R., & Grossmann, L. (2026). Matrix-controlled iron bioavailability in unrefined whole-pulse low-moisture extrudates. Current Research in Food Science, Article 101589. https://doi.org/10.1016/j.crfs.2026.101589

Image Credits: AI Generated

DOI: 10.1016/j.crfs.2026.101589

Keywords: iron bioavailability, yellow bean, pulses, extrusion, phytic acid, flavonoids, Caco-2 cells, plant-based nutrition, iron deficiency, food matrix, snack foods, non-heme iron

The motivation behind the work lies in one of the most stubborn limitations of conventional lightweight alloys. Aluminum alloys in the AA2XXX and AA7XXX families, the workhorses of the aerospace industry, rely on fine precipitates for their strength, but those precipitates dissolve or coarsen above roughly 200 degrees Celsius, causing properties to collapse. For applications such as supersonic aircraft, where skin temperatures can climb well beyond that threshold, designers have had no choice but to turn to heavier titanium or nickel-based materials, sacrificing fuel efficiency and increasing carbon dioxide emissions. Cerium-containing aluminum alloys offer a way out of this bind. When cerium is added to aluminum, it forms an Al11Ce3 intermetallic phase whose slow diffusion and low solubility in the aluminum matrix make it exceptionally resistant to coarsening, with stability demonstrated up to at least 350 degrees Celsius. Cerium is also a relatively abundant rare earth element, currently lacking high-volume applications, and is recovered as a byproduct of refining more valuable rare earths, which makes the alloy family economically attractive.

The alloy was prepared by melting high-purity aluminum with aluminum-cerium and aluminum-magnesium master alloys at 850 degrees Celsius and casting the melt into a graphite mold. Inductively coupled plasma analysis confirmed the composition at 10.096 percent cerium and 4.676 percent magnesium by weight, with only trace iron and silicon. The researchers deliberately chose the 4 percent magnesium content based on CALPHAD thermodynamic modeling, which showed that deforming the material at or just below the solvus of a τ-Al13CeMg6 intermetallic and above the metastable β-AlMg solvus would allow the high dislocation density generated during deformation to stimulate the nucleation of fine precipitates either during processing or upon subsequent cooling. The cast rods were then hot extruded at 300 degrees Celsius to a final diameter of 9.5 millimeters, an 86 percent reduction in cross-sectional area, using conditions deliberately kept within the envelope of conventional industrial practice.

Microstructural characterization revealed exactly why the extrusion was so effective. X-ray diffraction, scanning electron microscopy, electron backscatter diffraction, differential scanning calorimetry and high-resolution transmission electron microscopy together painted a detailed picture of the transformation. In the as-cast condition, the alloy displayed the classic script-like eutectic structure of Al11Ce3 intermetallics distributed unevenly through a large-grained aluminum-magnesium matrix, with an average grain size of about 23.6 micrometers. After extrusion, the grains shrank to roughly 7.2 micrometers and the intermetallic particles were broken down and aligned into the extrusion direction, with the average dispersoid size falling from 3.57 to 1.91 micrometers. The dislocation density, calculated from kernel average misorientation measurements, roughly doubled, and a brass-type crystallographic texture emerged. Crucially, when the extruded material was annealed at 300 degrees Celsius for up to 100 hours, neither the grain size nor the dispersoid size changed to any statistically significant degree, confirming that the refined structure is thermally stable.

The mechanical property gains were striking across the board. Yield stress and tensile strength increased by factors of roughly 2.5, while elongation at failure jumped from 3.8 percent to 17.2 percent. Hardness rose from 98 HV in the cast state to 114 HV after extrusion. The simultaneous improvement in strength and ductility, a combination that is often difficult to achieve, was attributed to the uniform refinement of the intermetallic distribution, the increased dislocation density and the development of texture. Fractographic analysis told a consistent story: cast samples failed along cleavage facets in a brittle manner, while extruded samples fractured through dimpled, ductile surfaces, reflecting intense plastic deformation before failure. The extruded material also reached a Young’s modulus of about 75 gigapascals.

Thermal endurance proved to be the alloy’s signature quality. After exposure to 300 degrees Celsius for 100 hours, the as-cast alloy retained 82 percent of its room-temperature strength, and the extruded version retained 88 percent. Fracture toughness, measured for the first time in any Al-Ce-Mg alloy using the single-edge bend method of ASTM E1820, reached 23 kilojoules per square meter in the extruded state, a value comparable to some of the highest figures reported for aluminum alloys, including aluminum-lithium systems and wire-arc additively manufactured Al-Si. After the same 100-hour anneal, 97.6 percent of that toughness was preserved. Compared with the commercial high-temperature alloy AA2618, which loses about 90 percent of its room-temperature strength at 300 degrees Celsius, the ternary alloy held on to roughly 40 percent of its strength, although it fell short of the binary Al-10Ce alloy, which retains about 70 percent.

The reason for that trade-off lies in the magnesium. Transmission electron microscopy revealed fine, nanoscale magnesium-rich precipitates both within the aluminum grains and along their boundaries, too small to be detected by X-ray diffraction or EBSD. Differential scanning calorimetry showed an endothermic dissolution event with an onset at about 215 degrees Celsius, and a weak exothermic peak on cooling at roughly 360 degrees Celsius, indicating that these precipitates dissolve as the temperature climbs and re-form when it falls. The researchers estimate that the magnesium-rich precipitates account for about 55 percent of the room-temperature flow stress, which explains why strength drops rapidly in the 150 to 250 degrees Celsius range and why the extra strength of the ternary alloy over the binary Al-10Ce is essentially erased above 250 degrees Celsius. The reversible nature of the dissolution and re-precipitation, however, means the material recovers its properties on cooling, ensuring excellent property retention through thermal cycling.

The study also documented an unusual deformation behavior: negative strain rate sensitivity at room temperature. Tensile tests across strain rates from 10^-5 to 10^-2 per second revealed serrated flow curves characteristic of the Portevin-LeChatelier effect, driven by dynamic strain aging as magnesium atoms diffuse toward and interact with moving dislocations. The strain rate sensitivity parameter reached about minus 0.03 at intermediate rates, a range similar to that observed in the commercial alloy AA5182, which contains 4.5 percent magnesium. The serrations vanished at both the fastest and slowest rates and disappeared entirely at 150 degrees Celsius, confirming the diffusion-controlled origin of the phenomenon and demonstrating that sufficient magnesium remains in solid solution even after processing.

By decomposing the strength contributions of different mechanisms, the team showed that the refinement from extrusion contributes about 106 megapascals to the yield stress, split roughly equally between the increased dislocation density and the finer grains and intermetallics, while magnesium in solid solution adds another 32 megapascals in the cast state. The most impressive single contribution, however, is strain hardening: the extruded ternary alloy hardens by about 190 megapascals between yielding and failure, nearly four times the strain hardening of the equivalent binary alloy, an effect the authors link directly to the nanoscale magnesium-rich precipitates. Taken together, the results establish extrusion-processed Al-10Ce-4Mg as a serious candidate for lightweight, temperature-resistant structural applications, from supersonic airframes to powertrain components, and demonstrate that the path from laboratory curiosity to industrial adoption may run through the most conventional of metalworking processes.

Subject of Research: Thermomechanical extrusion processing of a ternary Al-Ce-Mg alloy to enhance strength, toughness and thermal stability.

Article Title: Effect of thermomechanical processing on mechanical properties and the microstructure of ternary Al-Ce-Mg alloy

Article References: Effect of thermomechanical processing on mechanical properties and the microstructure of ternary Al-Ce-Mg alloy. (n.d.). https://doi.org/10.1007/s44492-026-00011-3

Image Credits: AI Generated

DOI: 10.1007/s44492-026-00011-3

Keywords: Al-Ce-Mg alloy, extrusion, thermomechanical processing, Al11Ce3 intermetallic, fracture toughness, high-temperature strength, Mg-rich precipitates, microstructure, dynamic strain aging, thermal stability, lightweight alloys, tensile properties