Mud and Sand Inspire a New 3D-Printable Food Ink for Safe Swallowing

Scientists have borrowed a trick from civil engineering — the humble mixture of mud and sand — to solve a stubborn problem in food science: how to turn a protein-rich emulsion into a printable ink that holds its shape, survives storage, and can be swallowed safely by people who struggle to eat. In a study published in Current Research in Food Science, a research team led by Yuanyuan Liu describes a high internal phase emulsion reinforced by two natural polysaccharides, gellan gum and xanthan gum, whose complementary roles mirror the way rigid sand grains and binding mud cooperate to give earthen materials both strength and workability.

The motivation is pressing. A rapidly aging global population, together with growing numbers of people living with dysphagia — difficulty swallowing — has created urgent demand for foods that are simultaneously safe, nutritious, and appealing. Such foods must meet strict texture standards to reduce the risk of aspiration, yet they also need to carry meaningful nutrition, particularly lipophilic bioactive compounds, to counter the malnutrition that often accompanies chewing and swallowing disorders. Traditional thickening systems built on starches or hydrocolloids fall short: they struggle to deliver high nutrient density, they cannot structure healthy lipids efficiently, and they tend to break down or separate during long storage.

The team’s starting point was a protein-based Pickering emulsion, a class of systems in which solid particles — rather than synthetic surfactants — adsorb at the oil–water interface and form a protective shell around droplets. The researchers built their interface from ovalbumin, the main protein of egg white, working together with tea polyphenols and hyaluronic acid. Ovalbumin’s amphiphilic character lets it anchor at the interface and form a film, tea polyphenols reinforce the particles through hydrogen bonding and hydrophobic interactions while adding antioxidant capacity, and hyaluronic acid thickens the interfacial layer. When the oil fraction is pushed above 74 percent, the result is a high internal phase emulsion, or HIPE: a material so packed with droplets that it behaves like a soft solid, self-supporting and stable, ideal for loading fat-soluble nutrients.

But stability alone was not enough. A HIPE’s solid-like rheology, the very property that makes it stable, also makes it difficult to process by conventional filling and molding, and even harder to shape with the precision that modern personalized nutrition demands. Enter 3D printing. Extrusion-based food printing promises digital control over both geometry and internal microstructure, which in turn governs how a food breaks apart in the mouth and how nutrients are released. The catch is that a good printing ink must be a rheological paradox: thin and flowing under the high shear of the nozzle, yet instantly stiff and self-supporting the moment extrusion stops.

To resolve that paradox, the researchers turned to the mud–sand analogy. Undissolved gellan gum particles, added at 0.3 percent, played the role of sand: rigid fillers that embed in the droplet network, anchor it physically, and boost mechanical strength. Xanthan gum, tested at 0.2, 0.6, and 1 percent, played the role of mud: its long molecular chains weave a continuous viscoelastic network through the aqueous phase, thickening the system, imparting the shear-thinning behavior needed for smooth extrusion, and reconnecting the gellan particles into a coherent whole. The base formulation — 25 percent composite aqueous phase and 75 percent soybean oil — was homogenized at 12,000 rpm to produce emulsions containing 75 percent oil, well into high internal phase territory.

Spectroscopic and scattering analyses confirmed that the additions were gentle on the protein. Fourier-transform infrared spectra showed that the amide bands of ovalbumin, near 1635 and 1534 per centimeter, remained essentially unchanged across all formulations, meaning the protein’s conformation was barely disturbed. X-ray diffraction revealed a broadly amorphous structure, with xanthan gum actually suppressing the local crystallization of tea polyphenols at higher concentrations, yielding a more uniform composite. Zeta potential measurements told a subtler story: adding gellan gum diluted the system’s net negative charge from about −32 to −26 millivolts, yet the steric hindrance and physical network of the undissolved particles more than compensated, and xanthan gum restored the potential to roughly −35 millivolts at the optimal dose.

Microscopy and stability testing made the synergy vivid. Confocal laser scanning images of the control emulsion showed heterogeneous, flocculated droplets with clear signs of coalescence — the thin interfacial film simply could not withstand the capillary pressures inside a HIPE. Gellan gum alone produced a bipolar droplet distribution, but the combination of gellan and xanthan gum produced small, evenly dispersed droplets locked inside a dense gel matrix. Under centrifugation, the control lost nearly 13 percent of its oil; the best dual-polysaccharide formulation lost none. After 30 days of refrigerated storage, every emulsion remained free of visible phase separation, and heat treatment at 85 degrees Celsius actually strengthened most of the modified systems, as denatured protein formed tougher interfacial films and hydrated gellan molecules tightened the gel network.

The rheological measurements revealed exactly why the material prints so well. All samples showed pronounced shear-thinning, and the storage modulus exceeded the loss modulus throughout, confirming solid-like behavior. As xanthan gum concentration rose, the storage modulus climbed from about 1049 pascals in the control to more than 2500 pascals, while the loss tangent fell — hallmarks of a stronger, more elastic gel. Critically, three-interval thixotropy tests showed that the xanthan-rich formulations recovered roughly 85 percent of their structure after 300 seconds of high shear, thanks to flexible xanthan chains that rapidly re-entangle and bridge the disrupted gellan particles. Yield points shifted to strains above 50 percent, meaning the ink resists deformation during handling yet flows cleanly through the nozzle.

Printing trials put those numbers to the test. The control emulsion exceeded its target dimensions by up to 110 percent, with broken filaments, blurred contours, and collapsed cylinders. Adding gellan gum helped, but deviations still reached 45 percent. The dual-polysaccharide inks, by contrast, achieved near-zero deviation — within a ±3 percent tolerance — producing cylinders and cuboids with crisp edges, uniform layers, and robust interlayer adhesion. The optimal formulation, 0.3 percent gellan gum with 0.6 percent xanthan gum, also proved the most resilient: it survived freeze–thaw cycling better than the 1 percent xanthan version, whose overly rigid network was punctured by growing ice crystals, and it showed the mildest oxidation during a week of storage at −4 degrees Celsius.

Perhaps most importantly for its intended users, the printed foods passed the international standard for dysphagia diets. In fork pressure and spoon tilt tests aligned with the IDDSI framework, the samples deformed under roughly 17 kilopascals — comparable to the force of the tongue during swallowing — broke into small, safe pieces with no large lumps, and held their shape on a tilted spoon, placing them at Levels 6 to 7, soft and bite-sized to easy-to-chew. After steam treatment, the printed constructs retained their form, held water well, and showed a tender texture with reduced adhesiveness, lowering choking risk. The mud–sand design, the authors conclude, offers a generalizable strategy for turning protein-based HIPEs into precision food inks — a step toward printed meals that are simultaneously beautiful, stable, nutrient-dense, and safe for those who need them most.

Subject of Research: Polysaccharide-reinforced protein-based high internal phase emulsions for 3D-printed dysphagia foods

Article Title: “Mud-Sand Structure”-Inspired Synergistic Reinforcement of Gellan Gum and Xanthan Gum on the 3D Printing Properties of Protein-Based High Internal Phase Emulsions

Article References: Xie, Y., He, C., Yu, X., Ma, J., Zhao, E., Liu, M., Zhang, H., Yuan, J., Zhou, Y., Zhu, Q., Cheng, Y., & Liu, Y. (2026). “Mud-Sand Structure”-Inspired Synergistic Reinforcement of Gellan Gum and Xanthan Gum on the 3D Printing Properties of Protein-Based High Internal Phase Emulsions. Current Research in Food Science, Article 101579. https://doi.org/10.1016/j.crfs.2026.101579

Image Credits: AI Generated

DOI: 10.1016/j.crfs.2026.101579

Keywords: 3D food printing, high internal phase emulsion, Pickering emulsion, gellan gum, xanthan gum, ovalbumin, dysphagia, rheology, food ink, IDDSI, tea polyphenols, hyaluronic acid