Researchers at the Iran University of Science and Technology have developed four hybrid auxetic metamaterial structures using PLA, achieving up to 6,024 J/kg specific energy absorption (SEA) under compression. The study, published in Scientific Reports on October 30, 2025, combines honeycomb, cubic, and tetrachiral unit cells to enhance energy absorption for lightweight applications such as crash protection and biomedical devices.
Combining proven designs for higher performance
The team selected the three unit cells based on previous research showing strong compressive performance and auxetic behavior. Instead of inventing new cell geometries, they combined the best-performing existing ones into four hybrid configurations: honeycomb–cubic (HC), honeycomb–tetrachiral (HT), tetrachiral–cubic (TC), and honeycomb–tetrachiral–cubic (HTC).
Each design was modeled using CATIA and fabricated on a Creality K1 3D printer. The parts were printed from PLA at 180 °C with 0.2 mm layers, 100 % infill, and a printing speed of 20 mm/s. Compression tests followed the ASTM D695 standard on a Santam STM-400 machine, while finite element simulations were performed in Abaqus/Explicit 2018.
HT structure triples the energy absorption of solid PLA
The honeycomb–tetrachiral (HT) structure achieved the highest energy absorption at 6,024 J/kg, approximately three times greater than that of solid PLA, which reached 1,810 J/kg. The next best performer, HTC, recorded 4,756 J/kg, followed by HC at 3,374 J/kg and TC at 2,101 J/kg. Despite being about 50 % lighter than the solid control, all hybrid structures absorbed significantly more energy, highlighting the effectiveness of combining auxetic and chiral geometries.
Why auxetic lattices excel under compression
The HT configuration outperformed the others due to its longer plateau region in the compression curve, allowing it to sustain energy absorption over a greater range of deformation. In comparison, the TC sample exhibited higher peak stress but a much shorter plateau, which limited its overall SEA.
All structures showed negative Poisson’s ratios between −1.0 and −1.7, confirming their auxetic character. The HC structure exhibited the most negative ratio at −1.7, while HTC balanced moderate auxeticity with more uniform deformation across its layers.
Simulations and real-world failure modes
The numerical simulations reproduced the experimental compression behavior with high accuracy. The study reported several distinct failure mechanisms, including cell collapse, cracking at honeycomb corners, and interlayer sliding, particularly evident in the TC structure. No delamination occurred, indicating excellent print quality. The authors noted that the small differences between the simulated and experimental results were largely due to the fully constrained boundary conditions used in the model, which do not replicate the slight real-world movements.
Deformation and von Mises stress distributions for HT, HC, TC, and HTC under compression. Images via Scientific Reports / Shahmorad et al. (2025).
Toward lightweight energy-absorbing materials
According to the researchers, these hybrid PLA metamaterials demonstrate that careful unit-cell selection and composition can outperform more complex multi-material or topology-optimized designs. The approach offers a practical and low-cost method for producing lightweight, energy-absorbing, or crash-resistant parts using standard FDM equipment.
The study suggests that such structures could also find applications in biomedical implants, protective devices, and other components where tailored mechanical response and weight reduction are essential. Future work will investigate scaling effects, dimensional optimization, and anisotropy in 3D printed PLA to further enhance performance.
Advancing energy-absorbing metamaterials
The study builds on a growing body of research exploring how 3D printed architectures can control deformation and energy dissipation. Earlier this year, Korean researchers developed a tactile sensor using auxetic metamaterials to enhance flexibility and strain sensitivity in soft electronics, while RMIT scientists introduced an ultra-stiff, energy-absorbing lattice aimed at improving safety and durability in construction applications. More recently, a collaboration between the University of Glasgow and Italian researchers produced a twist-to-absorb metamaterial that dissipates impact energy through controlled torsion, highlighting the expanding role of architected materials in vehicle and infrastructure safety.
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Feature image shows observed failure modes in the tested metamaterial structures after compression testing. Image via Scientific Reports / Shahmorad et al. (2025).
