Researchers at EPFL and Uppsala University have developed a novel technique that enables the fabrication of composite materials via volumetric additive manufacturing (VAM), overcoming long-standing limitations in the field. Published in ACS Materials Letters, the study demonstrates how post-printing hydrogel infusion can convert transparent VAM-printed parts into functional composites with high filler content.
Overcoming transparency constraints in VAM
VAM processes require light to pass cleanly through a resin vat to polymerize structures volumetrically. This restricts material choice to transparent photopolymers and excludes fillers, which scatter light. Composite resins, therefore, are mostly incompatible with current VAM technologies.
To address this, the team employed Xolography, a VAM method that uses intersecting light beams to define polymerization zones within a vat. Instead of printing with filled resins, they printed transparent hydrogels first and infused them with metal ions post-printing. The composite fillers were then formed in situ by chemical precipitation, enabling the creation of magnetic and conductive parts without affecting print quality.
Magnetic and conductive composites with tunable properties
The researchers demonstrated two main applications; magnetic iron oxide nanoparticles (IONPs) were grown within the hydrogels using iron salts and ammonia. Up to 65 wt% loading was achieved, a significant milestone given the usual 0.5 wt% limit for light-scattering fillers in VAM. Additionally, silver nanoparticle composites were created via reduction of infused silver nitrate, producing conductive structures capable of closing LED circuits.
Properties such as magnetic strength, electrical conductivity, and mechanical behavior could be tuned by varying temperature, infusion time, and the number of reaction cycles. While higher temperatures improved magnetization, they also reduced structural integrity, highlighting a trade-off between performance and durability.
Multimaterial and spatially controlled structures
One of the study’s most innovative aspects was its demonstration of spatially localized material transformation. By selectively infusing regions of the hydrogel with metal ions prior to the precipitation step, researchers created multimaterial structures with embedded actuation zones.
Demonstrator devices included a pendulum with a magnetic joint that could be rotated using an external magnet and a spring structure with responsive behavior driven by filler placement. This approach could enable soft robotics, interactive devices, or smart structures with site-specific functionality, all printed as a single body, without assembly.
Post-fabrication transformation over resin formulation
Instead of developing new resin blends to accommodate fillers during printing, the method reframes the problem by applying post-fabrication chemistry. A single hydrogel formulation becomes a modular platform for different composite functions, streamlining the material development pipeline.
Though limited by degradation during multiple infusion cycles, the authors propose switching to more chemically robust polymers to support higher performance applications.
Broader implications and future directions
This research could unlock new possibilities in biomedical devices, sensors, robotics, and electronics, where multifunctional materials and geometric freedom are essential. The infusion-based approach is also compatible with other VAM platforms reliant on resin transparency, including multiphoton lithography.
A patent has been filed for the process, and supporting videos show remote control of printed composite structures, underscoring its potential.
As volumetric printing continues to evolve, this hydrogel infusion method may shift how the industry approaches functional material integration.
Volumetric and hydrogel-based additive manufacturing evolve
Volumetric additive manufacturing (VAM) has seen rapid development in recent years. Earlier this year, researchers at EPFL unveiled a MEMS-based holographic VAM platform that leverages micro-mirrors to enhance resolution, energy efficiency, and scalability, offering a promising upgrade to tomographic printing systems. Separately, Xolo’s launch of the Xube² volumetric printer has extended Xolography’s commercial potential, supporting applications from soft materials to optics.
In parallel, the National Research Council of Canada developed an automatic exposure system for VAM, improving process control by compensating for variable resin properties and reducing overexposure during curing.
This latest study by Ji et al. complements those advances by addressing a critical material limitation: the incompatibility of conventional VAM processes with composite resins. By enabling post-print infusion and in situ nanoparticle synthesis, the researchers introduce a practical route to producing functional composites, including magnetic, conductive, and spatially programmable structures, within VAM workflows.
What 3D printing trends should you watch out for in 2025?
How is the future of 3D printing shaping up?
To stay up to date with the latest 3D printing news, don’t forget to subscribe to the 3D Printing Industry newsletter or follow us on Twitter, or like our page on Facebook.
While you’re here, why not subscribe to our YouTube channel? Featuring discussion, debriefs, video shorts, and webinar replays.
Featured image shows VAM printed hydrogel to functional composite. Image via ACS Materials Lett.
