Tensegrity metastructure with tunable stiffness, strength, and energy dissipation

Design and fabrication of architected multi-material lattices with tunable stiffness, strength, and energy absorption

Energy‐dissipating mechanical metamaterials possess broad applications where absorbing shocks and isolating vibrations within monolithic and sandwich composite structures are required. This study presents the design of a novel bidirectional mechanical metamaterial with tunable stiffness and energy dissipation. By leveraging the phenomenon of Coulomb friction, the metamaterial dissipates energy when a small gap closes and two walls slide across one another under planar loading. The conceptual design of the metamaterial is parameterized, so the material behavior can be tailored to a particular application. A computational framework is built, using finite element analysis and a multi‐objective genetic algorithm to maximize the volumetric energy dissipation such that the unit cell does not undergo plastic deformation. The finite element mesh used in this analysis is first parametrically optimized to minimize simulation time while remaining within a global error threshold. The optimal unit cell is arrayed into a bulk material, formed into a hollow cylinder, and simulated under a compression cycle for different metamaterial densities. A prototype of the hollow cylinder is 3D printed via fused deposition modeling and is tested. Both the simulated and experimental results demonstrate the repeatability of the energy‐dissipating property with a strong correlation.

Architectured ceramics with tunable toughness and stiffness

Static and dynamic properties of a perforated metallic auxetic metamaterial with tunable stiffness and energy absorption

A Supramolecular Polymer Formed by Small Molecules

Tunable negative stiffness spring using maxwell normal stress

Superior material properties have been recently exhibited under the concept of biomimetic designs, where the material architectures are inspired by nature. In this study, a computational framework is developed to present novel architectured bi-material structures with tunable stiffness, strength, and toughness to be used for additive manufacturing (AM). The structure of natural nacre is mimicked to design robust multilayered structures constructed from hexagonal brittle and hard building blocks bonded with soft materials and supports. A set of computational models consisting of fully bonded zones, while allowing for interlayer interactions are created to accurately mimic the interplay between the hard and soft organic phases. As required for such complex designs, the numerical constraints are properly set to run quasi-static non-linear explicit analysis, which allow for a 3× faster analysis with higher efficiency and 2× lower computational cost, when compared to static analysis. The models are used to assess the stiffness, strength and toughness of bi-material beams when subjected to a flexural three-point bending load. The influence of structural features like the soft-to-hard volume ratio (i.e. the distance between each building block, its aspect ratio, and overlap length), material features (e.g. the stiffness ratio of the hard-to-soft phases), the plastic strain failure of soft phase, and AM features (e.g. different types of within-layer/sandwiched supports) are systematically investigated. The results revealed that the toughness of the architectured beams was enhanced by up to 25% when compared to a monolithic structure. This improvement is due to the frictional tile sliding in the brittle phase and the extensive shear plastic deformation of the soft interfaces. This work provides compatible designs to facilitate the AM of nacre-based bi-martial structures with balanced/tailored mechanical performance and to understand the influence of the architectural parameters.

Regulation of electrospun scaffold stiffness via coaxial core diameter

Multi Jet Fusion (MJF) is a 3D-printing process capable of fabricating large-scale polymer structures. Herein, we present a framework for MJF-printed lattices with tunable stiffness and strength based on an empirical analysis of structural behavior.

Nanoparticle networks, characterized by strong interparticle adhesion and structural rigidity, are typically considered resistant to dynamic reorganization under mechanical perturbation, unlike thixotropic gels or granular materials that fluidize when agitation exceeds critical thresholds. Using high-resolution atomic force microscopy (AFM) coupled with dynamic mechanical analysis, this study examines a frictional unlocking mechanism in porous sintered silver nanoparticle networks, where small oscillatory strains trigger a reversible transition from a purely elastic to elastoplastic response. This nanoscale reorganization occurs through intermittent particle rearrangements that enable localized mobility while maintaining global network integrity, mediated by the conversion of oscillatory energy into grain-boundary shear. The results indicate that this mechanism represents one stage of a broader constrained densification pathway, in which nanoparticle networks evolve from a fluid-like, loosely connected state through distinct intermediate metastable configurations, each separated by well-defined energy barriers, before reaching a reversible solid-like state. This stepwise progression, quantified through energy dissipation measurements and microstructural analysis, contrasts with classical unjamming or liquefaction phenomena by preserving the structural continuity throughout the transition. By establishing links between nanoscale energy dissipation pathways and macroscopic mechanical responses, this work provides a framework for designing materials with tunable stiffness and dynamic adaptability. The findings are relevant to technologies such as electronic interconnects with stress-adaptive properties, powder-based additive manufacturing processes, and energy storage systems, where controlled nanoparticle mobility under operational stresses is important for long-term performance.

Through the use of mechanical reinforcement of collagen matrices, mechanically strong and compliant 3D tissue mimetic scaffolds can be generated that act as scaffolds for soft tissue engineering. Collagen has been widely used for the development of materials for repair, augmentation or replacement of damaged or diseased tissue. Herein we describe a facile method for the layer-by-layer fabrication of robust planar collagen fiber constructs. Collagen gels cast in a phosphate buffer were dried to form dense collagen mats. Subsequent gels were layered and dried atop mats to create multilayer constructs possessing a range of tunable strengths (0.5 - 11 MPa) and stiffness (1 - 115 MPa). Depending on processing conditions and crosslinking of constructs, strain to failure ranged between 9 to 48%. Collagen mats were constructed into hernia patches that prevented hernia recurrence in Wistar rats.

Liquid crystals may possess macroscopically aligned structural, electrical and optical properties when oriented in external fields which leads to a wide range of applications including optical filters, displays, and data storage devices. Combining the properties of thermosets [1, 2] with the properties of liquid crystals (LC) is a logical step towards creating new materials. The development of liquid crystalline thermosets (LCT) has been motivated by their potential use in structural applications and the need for more adaptable polymeric materials with tunable strength and stiffness as well as tailored mechanical anisotropy. It is known that mechanical properties of conventional thermosets are determined by many factors including curing agent, filler, degree of cure, crosslink density, glass transition temperature, and accelerator. In LCT's all of these factors will ultimately be controlled by the both the molecular organization and orientation of the LC phase.

Hydrogels prepared from natural polymers, such as silk fibroin, are useful in the field of tissue engineering due to their biocompatibility, biodegradability, and biological performance. However, poor mechanical properties can limit their broader utility. This study investigated reinforcing enzymatically crosslinked silk hydrogels with 130 nm silk nanoparticles (SNPs) to generate silk-silk composite materials with tunable strength and stiffness. The strength of the materials was dependent on SNP concentration, and hydrogels with Young's moduli of 14, 34, and 67 kPa were fabricated by adding no SNPs, 2 mg/mL SNPs, and 4 mg/mL SNPs, respectively. These methods were applied to silk bioinks using Freeform Reversible Embedding of Suspended Hydrogels (FRESH) 3D printing to fabricate complex 3D structures with control of elasticity and modulus. Cylinders with Young's moduli of 17, 35, and 58 kPa were obtained with no SNPs, 2 mg/mL SNPs, and 4 mg/mL SNPs, respectively. SNPs were also preloaded with epidermal growth factor (EGF), relevant for tissue development and wound healing, and sustained release was achieved for over 15 days when embedded in hydrogels. Pilot studies of dermal fibroblast encapsulation in SNP-reinforced silk hydrogels demonstrated cytocompatibility. Tunable silk hydrogels reinforced with SNPs provide application-specific scaffolding for a variety of biomaterial and tissue engineering applications.

Cellular materials are gaining popularity as constituent materials in end-use products due to their tunable stiffness and energy absorption capabilities. Additive manufacturing technologies have allowed the fabrication of these porous materials with engineered topologies. Previous works have characterized the mechanical response of cellular materials mainly under static loading scenarios; their fatigue behavior is a complex phenomenon, not yet thoroughly studied. In this work, we exploited the benefits of fused filament fabrication to build thermoplastic polyurethane cellular materials and experimentally characterize their properties under static and dynamic loadings. Three different topologies (hexagonal, re-entrant, and square) with same volume fraction were studied. A geometrical assessment was conducted on specimens to evaluate the accuracy of the selected fabrication process. Compression-compression fatigue tests (2 Hz, R = 0.1) resulted in the construction of stiffness degradation and energy absorption ability plots. Samples exhibited a loss of 30% of their original rigidity and 50% of their normalized energy absorbed after 100,000 loading cycles. Our findings comparatively illustrated the advantages between different cellular materials and the selection of thermoplastic polyurethane as constituting material in terms of fatigue life performance.

Helmholtz resonators are a classic means to absorb low frequency acoustic waves with great effectiveness and straightforward implementation. Yet, traditional Helmholtz resonators are tuned to absorb a specific frequency of wave energy and are unable to adaptively tailor damping capability. On the other hand, recent research on elastomeric metamaterials offers concepts for large and tunable damping properties using internal constituents that buckle to trap large elastic energy when subjected to geometric or load constraints. The research reported here draws from the principles of Helmholtz resonance and constrained metamaterials to device a resonant metamaterial with tunable acoustic energy dissipation. Using the fluid-structure interaction of an internal beam-like member with the resonator chamber, the metamaterial absorbs acoustic waves at a target frequency and tailors energy dissipation by changing external constraints that relatively magnify or suppress the interaction between acoustic pressure and damped beam member. An analytical model is developed to qualitatively characterize the behavior of the metamaterial observed in the laboratory. From the combined experimental and analytical studies, it is found that the metamaterial may significantly reduce the sound pressure level at the targeted frequency range while modulating the broadness of the absorption effect by way of external load control.