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Hollow Auxetic Polymer Structures with Manufacturing-Constrained Design and Mechanical Validation
Finlay Bridge1, Rakan Albarakati2, Hany Hassanin3
1Mechanical Engineering, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK.
Polymers
|April 14, 2026
Summary
This study introduces a new method for creating hollow auxetic lattices using stereolithography (SLA), optimizing them for lightweight designs. The hollow SLA lattices offer significant density reduction and improved specific stiffness for specialized applications.
Area of Science:
- Additive Manufacturing
- Materials Science
- Mechanical Engineering
Background:
- Hollow auxetic structures offer lightweight design advantages but are primarily studied in laser powder bed fusion (LPBF) metals.
- Stereolithography (SLA) presents an alternative additive manufacturing method for creating complex lattice structures.
Purpose of the Study:
- To develop and validate a manufacturing-constrained design framework for hollow hybrid re-entrant chiral lattices using SLA.
- To optimize the geometry of these lattices for desirable mechanical properties and manufacturability.
Main Methods:
- Unit cell parameterization (chiral angle, strut length, internal diameter) and integration of drainage features for SLA printing.
- Minimum internal diameter study to define the printable design window.
- Central composite design coupled with finite element analysis (FEA) for response surface mapping and optimization.
- Compression testing of printed unit cells and 3x3x3 lattices.
Main Results:
- An optimized geometry (θ = 15°, L = 3.5 mm, d = 1.68 mm) was identified with a predicted unit-cell Poisson's ratio of -1.17.
- Printed hollow lattices exhibited rotation-dominated auxetic deformation, with measured Poisson's ratios of -0.68 (unit cell) and -0.29 (3x3x3 lattice).
- Compared to solid lattices, hollow lattices achieved 42.4% density reduction and 68.9% specific stiffness increase, with a 5.2% specific peak strength increase, but a 25.6% decrease in specific energy absorption.
Conclusions:
- The study provides practical design guidance for creating manufacturable hollow SLA auxetic lattices.
- These structures are particularly suitable for lightweight and stiffness-limited applications where low mass and high specific stiffness are prioritized over energy absorption.
- The developed framework enables the design of advanced auxetic materials with tailored properties for specific engineering challenges.
