Development, 3D printing, and mechanics of novel auxetic unit cell monostructures

• Introduces a new 3D S-shaped monostructure using mechanics-based and additive mindset approaches. • Explores the relationship between structural behavior and geometrical features using experimental and numerical methods. • Outperforms existing re-entrant and star auxetic structures regarding spatial auxeticity, negative Poisson's ratio, linearity, and elasticity. • The scalability, printability, and tailorability of the S-shaped monostructures are suitable for the accelerated development of translatable biomedical implants. • Identifies rigid body motion as the primary deformation mechanism in the S-shaped unit cell, while material and architecture contribute to the overall behavior of re-entrant and star structures. Complex structures with unique mechanics are pivotal to advancing additive manufacturing, enabling applications where traditional methods are impractical. This study presents a novel 3D auxetic S-shaped monostructure designed for scalability, tunability, and printability using vat photopolymerization. Unit cell geometries were fabricated and experimentally evaluated under quasi-static loading conditions, with full-field analyses providing insights into their structural performance. Benchmarking against common auxetic structures (re-entrant and star topologies) highlighted the superior capabilities of the proposed design. The S-shaped monostructures exhibited geometric insensitivity in their force-displacement responses, with a stiffness of ∼180 N/m, withstanding large displacements of 11 mm without fracture or self-contact and supporting forces up to 1.8 N ( i.e. , 95 times their weight) before fully recovering upon unloading. Computational and experimental results demonstrated robust spatial auxeticity, persisting up to 85 % of axial global displacement due to geometry-driven rigid body motion, independent of base material properties. The S-shaped structures achieved superior auxetic performance ( ν m a x ≈ −0.43) compared to re-entrant ( ν m a x ≈ −0.30) and star ( ν m a x ≈ −0.05) counterparts, with a monotonic and reversible auxetic response throughout loading. Strain contour analyses from digital image correlation validated the reduced stress concentrations and rigid body-dominated mechanism. The exceptional auxeticity and mechanical resilience of the S-shaped monostructures suggest promising applications in advanced designs, including 3D stackable configurations for impact mitigation applications.