Ultra-stiff, lightweight, and high energy-absorbing 3D printed elastomeric foam lattices via a hierarchical grid-stiffened assembly and UV-thermal curable strategy

Lightweight materials relying on multiple ordered architected systems that emerge as next-generation shock-absorbing and high-impact applications with exclusive mechanical performances, but integrating and precisely fabricating them effectively into a single enclosed system remains a challenge. Here, a foam-integrated lattice design strategy is introduced, combining grid-stiffening guided topology optimisation to design metamaterials and 3D-printed elastomeric foams to fabricate designed complex structures. Spatially equivalent grid-assisted hierarchical architecture lattices were generated and validated by experimental and numerical simulations. A dual curable mechanism is utilised via vat photopolymerization and thermal foaming process by formulating dynamically curable polyurethane resin with thermally expandable microspheres. 3D printed structure exhibits a 1.7-fold expansion with a reduced density of 215 kg/m³ with high resolution and accuracy. Upon these features, lattice (star-diamond interwoven) delivered outstanding performance, achieving 600% stiffness and 1100% strength in non-foamed condition, and reaching 0.84J with an energy absorption efficiency of 48% (240% higher than non-foam) with foam integration, compared to the Kelvin lattice. Synergistical outcome revealing that closed cell foam formation on hierarchical structures with elastomeric crosslink functionality is well-bounded. The integrated design confirms further superior cushioning and energy absorption in shoe sole prototypes, establishing a scalable framework for precision-tuned architected foamed lattices in impact-mitigating applications.