A team from École Polytechnique Fédérale de Lausanne (EPFL) has unveiled a breakthrough in vat photopolymerization (VP), demonstrating a hydrogel-based technique that enables the 3D printing of ceramics and metals with far lower shrinkage than previously possible. Published in Advanced Materials on September 24, 2025, the study shows how repeated infusion–precipitation cycles transform printed hydrogel templates into dense, architected structures with shrinkages as low as 20% and material densities exceeding 80%.
Overcoming limitations in vat photopolymerization
Vat photopolymerization (VP) is one of the most widely used additive manufacturing technologies for polymers, valued for its fine resolution and rapid build speeds. Extending VP to ceramics and metals, however, has remained a challenge.
Traditional approaches often rely on particle-filled slurries, where ceramic or metal powders are mixed into a photosensitive resin. While effective in theory, this increases viscosity and light scattering, making it difficult to print fine features and often leading to poor surface quality. Hybrid photoresins, which embed inorganic components directly into the resin chemistry, offer better printability but restrict the range of possible compositions.
A more versatile alternative has been the use of aqueous metal salt solutions. These allow for greater material diversity and avoid light scattering issues. Yet they are accompanied by a critical drawback: extreme shrinkage during thermal conversion. Structures can shrink by 50–90%, leading to warping, cracks, and porosity that compromise mechanical integrity. This shrinkage problem has been the single largest barrier to practical adoption of VP for dense ceramic and metal parts.
A hydrogel-driven infusion–precipitation process
To overcome these limitations, the EPFL team developed a process that decouples printing from material loading. Instead of directly embedding powders or salts into a resin, they first print a “blank” hydrogel scaffold using standard digital light processing (DLP).
These hydrogel templates are then infused with metal salt solutions. Rather than immediately converting them into ceramics or metals, the researchers trigger an in situ precipitation step: a chemical reaction inside the hydrogel that transforms the dissolved metal ions into nanoparticles distributed throughout the structure.
By repeating this infusion–precipitation cycle multiple times, the team progressively increases the concentration of metal within the hydrogel. In some cases, loadings reached nearly 80 wt%, far beyond what conventional slurry-based or hybrid resin methods can achieve.
The final step is thermal treatment. Once dried and heated, the nanoparticle-rich hydrogel is converted into a dense ceramic or metal structure that closely retains the shape of the original printed template. Because so much inorganic material is already present before conversion, the overall shrinkage is drastically reduced compared to earlier methods.
High-density, low-shrinkage results
Using their infusion–precipitation approach, the researchers fabricated a range of structures including iron oxide (Fe₂O₃), strontium hexaferrite (SrFe₁₂O₁₉), iron, copper, and silver. Across these compositions, shrinkage was reduced to around 20–40%, compared to up to 90% with previous hydrogel infusion additive manufacturing (HIAM) techniques.
Material density was also significantly improved. Final parts reached 80–90% of their theoretical densities, a level that delivers far greater mechanical stability than earlier processes. In compression tests, iron gyroid lattices produced with the new method withstood stresses around 25 times higher than those made with conventional HIAM, showing compressive strengths of approximately 5 MPa.
Dimensional fidelity was another key outcome. Micro-CT scans revealed close alignment between printed parts and their CAD models, with deviations generally within tens of microns. Even at centimeter scale, structures such as gears and stents maintained their intended geometry with minimal warping, a major improvement over earlier methods where large shrinkage often led to distortion.
The team also demonstrated the ability to fabricate fine features, producing silver gyroids with wall thicknesses below 100 μm, dimensions that are challenging to achieve with powder-based methods like selective laser sintering (SLS), particularly for highly reflective metals such as copper and silver.
Expanding applications for functional ceramics and metals
The reduced shrinkage and higher density enabled by this method open up new possibilities for vat photopolymerization beyond fragile prototypes. Dense, architected metals and ceramics can now be manufactured with mechanical integrity suitable for practical use.
In the biomedical field, for example, the researchers fabricated iron-based stents that retained their tubular geometry without warping, a demonstration of how the process could support the development of implants and other medical devices requiring both fine resolution and robustness.
Energy-related systems stand to benefit as well, since architected ceramics and metals are central to batteries, fuel cells, and catalytic reactors, where porosity control and dimensional fidelity play a decisive role in performance.
The process also extends to functional ceramics. By infusing iron oxide composites with strontium salts, the team produced 3D architectures of strontium hexaferrite, a hard magnetic ceramic that displayed strong magnetization. This suggests new opportunities for integrating magnetic functionality into lightweight, architected structures.
More broadly, the ability to produce fine, high-density lattices could accelerate research into metamaterials and sensing devices, where architecture often dictates performance more than composition alone.
Rather than replacing existing technologies such as selective laser sintering (SLS), the researchers emphasize that their approach is complementary. SLS is well suited for larger parts with wall thicknesses above 300 μm, but it struggles to achieve sub-100 μm features, particularly with highly reflective metals like copper and silver. By contrast, the hydrogel infusion–precipitation strategy excels at these dimensions, offering a cost-effective and accessible alternative for applications where precision and material versatility are key.
Hydrogels in additive manufacturing
Hydrogels have become an increasingly important medium in additive manufacturing research due to their versatility as printable scaffolds. Earlier this year, researchers demonstrated how volumetric additive manufacturing could enable the production of composite materials via hydrogel infusion, highlighting the potential for rapid multi-material fabrication.
In another study, Caltech advanced metal 3D printing through hydrogel infusion additive manufacturing, showing how polymer templates can be transformed into functional metal structures. Hydrogels have also been explored in bioprinting and space applications, from xolography-based tissue engineering to improving radiation protection for astronauts.
The latest work from EPFL builds on this momentum by addressing one of the key limitations of hydrogel-based approaches, the severe shrinkage during conversion, and offering a pathway to dense, mechanically robust ceramics and metals.
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Featured image optical images of centimeter-scale Fe. Image via Daryl Yee et al./EPFL.
