Architected fillers redefine composite design
Researchers at Tampere University see 3D-printed particle shape as a new design tool for composites. Conventional composite fillers come in simple shapes such as spheres, plates or fibres, set by how they are synthesised or milled, and usually with a spread of sizes. The research led by Adel Badria, Postdoctoral Researcher at Tampere University, deals with architecturally engineered fillers – in other words, polymer fillers designed to have specific shapes. The research is based on an approach in which the 3D geometry of each particle is designed and printed in accordance with the requirements.
Using high-resolution 3D printing (Digital Light Processing (DLP), Badria and his team produced large numbers of identical sub-millimetre architected fillers, such as cubes and four-armed tetrapods, and embedded them in silicone. Changing the filler shape gave clearly different mechanical behaviour under compression: Tetrapods were the more efficient reinforcers, making the composite up to 12.8 times stiffer than the unfilled silicone and outperforming cubes of matching size, even per unit of filler. The largest cubes (1 mm³) reinforced least, but they were the only fillers to show a reproducible stress plateau under compression, a signature that no other geometry reproduced.
Complex particle shapes in this submillimetre range are hard to produce at scale because they are too large to make by chemical synthesis and too small to machine. As a result, they have rarely been available in controlled, repeatable shapes, and their effect on composites has not been studied systematically. The new work provides an experimental route to test how filler geometry governs composite mechanics and gives engineers a way to tune the stiffness and deformation response of soft materials by changing filler architecture, not only the material.
“Printing removes that barrier and turns particle shape into a design parameter that can be chosen deliberately, alongside the choice of material,” Adel Badria says.
Potential applications in soft robotics
Designing performance through geometry can also reduce the need to develop new material formulations, and the same base materials can be given different mechanical properties simply by changing filler shape.
In the future, Badria expects to see that this fundamental study might inspire new applications in soft robotics, where components need tailored stiffness; biomedical materials and devices with stiffness matched to tissue; and printed scaffolds for tissue engineering.
The article also presents a systematic method for comparing the geometries of fillers in a fair manner by normalising stiffness according to the physical amount of filler that can be incorporated into each composite, and by describing how each composite fractures.
"Instead of asking only what a filler is made of, we can now ask what shape it should have. 3D printing lets us design that shape and produce it in batches," Adel Badria concludes.
The article 3D-Printed architected fillers in soft composite matrices: A systematic framework for geometry-dependent mechanical characterisation was published in Materials & Design (Elsevier) on 5 November 2026.
The research was funded by the Research Council of Finland through the PROFI7 profiling programme SUSBIO (grant no. 352754).
