Bio-composite design and 3D printing of soft multi-functional meta-structures with tuneable quasi-constant force

Rahmani, K ORCID: https://orcid.org/0000-0002-0815-1562, Malekmohammadi, H, Haque, AM, Karmel, S, Branfoot, C, Pande, I, Breedon, P ORCID: https://orcid.org/0000-0002-1006-0942 and Bodaghi, M ORCID: https://orcid.org/0000-0002-0707-944X, 2025. Bio-composite design and 3D printing of soft multi-functional meta-structures with tuneable quasi-constant force. Applied Materials Today, 47: 102961. ISSN 2352-9407

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Abstract

This study presents a novel, 3D printable, multifunctional bio-composite material system for quasi-zero stiffness (QZS) mechanical metamaterials, transitioning from material development to structural implementation. Bio-based thermoplastic polyurethane (TPU) is reinforced with 3–5 wt.% bamboo charcoal (BC), 1 wt.% carbon nanotubes (CNT), and extruded for 3D printing via fused filament fabrication (FFF). The newly developed bio-composite shows up to 86 % strength enhancement and 35 % reduction in flammability. A surrogate-based optimisation method is implemented to calibrate a second-order Ogden hyper-elastic model using tensile data, enabling accurate prediction of nonlinear mechanical behaviours. Inspired by the human ribcage, QZS meta-structures were designed with dual-arched geometries and fabricated using the optimised TPU/BC/CNT composite. A finite element model is developed to digitally design the meta-structure and carry out a parametric study. Experimental and computational analyses demonstrate a materially tuneable constant-force plateau (e.g., 2.3–5.12 N) extending across a 6 mm displacement range, with excellent agreement between FEM and test results. Notably, the composite-based QZS structures show an 88 % increase in cyclic energy dissipation versus pure TPU. This response exhibits only limited early-cycle Mullins-type softening that stabilises by 10 cycles, retains 98 % of the maximum force at 1000 cycles, and remains durable under repeated loading-unloading. A modular triple-unit configuration further triples the force capacity without compromising QZS behaviour. This material-to-structure integration provides a scalable, sustainable pathway for engineering adaptive, load-bearing systems applicable to soft robotics, automotive interiors, and protective medical devices where force regulation, overload protection, safety, and comfort are desired.

Item Type:	Journal article
Publication Title:	Applied Materials Today
Creators:	Rahmani, K., Malekmohammadi, H., Haque, A.M., Karmel, S., Branfoot, C., Pande, I., Breedon, P. and Bodaghi, M.
Publisher:	Elsevier BV
Date:	December 2025
Volume:	47
ISSN:	2352-9407
Identifiers:	Number Type 10.1016/j.apmt.2025.102961 DOI 2517046 Other
Rights:	© 2025 The Author(s). This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
Divisions:	Schools > School of Science and Technology
Record created by:	Jeremy Silvester
Date Added:	24 Oct 2025 08:51
Last Modified:	24 Oct 2025 08:51
URI:	https://irep.ntu.ac.uk/id/eprint/54618

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