A modular metamaterial mimics DNA geometry to combine twist compression, tunable stiffness, fast recovery, and reusable shock absorption for robotics and impact systems.
(Nanowerk Spotlight) Across sectors as varied as robotics, aerospace, and protective equipment, engineers face a recurring dilemma. How do you build structures that are strong but not brittle, lightweight but not fragile, and flexible without being uncontrollable? Materials are often good at one of these things, but not all three. Soft foams, for instance, cushion well but lose their shape over time. Rigid frameworks carry load efficiently but fail completely when pushed beyond their limit. And most materials, once deformed, do not recover without help.
The problem is not just about material choice. It is also about geometry — how internal structures distribute force, absorb energy, and return to their original shape. Traditional engineering tends to focus on the chemistry and bulk properties of materials. But in nature, geometry plays a central role. The flexibility of tendons, the coiled strength of seed pods, the resilience of a strand of DNA — these arise not from rare materials, but from how form guides function. These biological structures adapt through shape and structure, not through active control or complex sensors. Translating this kind of passive adaptability into engineered materials remains a challenge.
Mechanical metamaterials offer one way forward. Built from repeating structural units, these materials achieve novel behaviors by design rather than by composition. Some can expand sideways when compressed, twist under linear loading, or shift stiffness depending on the applied force. However, many of these systems are limited in how they respond to complex, multidirectional loads. Most cannot fully recover after being deformed. Others operate well under lab conditions but degrade after repeated use.
Researchers in China have developed an approach that addresses these limitations through a modular structure inspired by the form of the DNA double helix. Published in Advanced Functional Materials (“Twist, Recover, Repeat: Helical Tensegrity Metamaterials with Compression‐Torsion Coupling, Negative Dissipation, and Programmable Energy Response”), the study introduces a reconfigurable metamaterial that couples compression with torsion and recovers its shape quickly and without external energy. The material also demonstrates a rare phenomenon where it releases more force during unloading than it absorbed during compression. This is known as negative energy dissipation.
This behavior is made possible by combining tensegrity principles with chiral geometry. The basic unit, called the Four Bar Tensegrity Module, or FTM, is composed of four curved rigid rods, flexible tension cables, and two parallel platforms. Left and right handed versions of this unit are designed to twist in opposite directions when compressed. When assembled into multicell arrays, these units enable coordinated movement across the structure. The geometry converts vertical compression into rotational motion, which changes how the material stores and releases energy.
Under static loading conditions, the structure behaves predictably and elastically. Compression causes both shortening and twisting, with a nonlinear increase in stiffness as deformation progresses. But when compressed quickly, the system does not have time to fully deform. Energy becomes trapped in the partially compressed geometry and is released forcefully when the load is removed. This creates a rebound effect, where the unloading force temporarily exceeds the applied force. The authors describe this as a dynamic inertial response governed by the geometry of the system.
Complete structural design and assembly strategy of the Four-bar Tensegrity Module (FTM). a) DNA replication process. Four-bar tensegrity elementary structure: b) right-handed unit and c) left-handed unit. d) Exploded view of the FTM structure. e) Internal mortise-tenon connection method of FTM and the physical FTM prototype. f) Comparison of interference behaviors between FTM and the traditional four-bar tensegrity platform under compression conditions. (Image: Reprinted with permission by Wiley-VCH Verlag) (click on image to enlarge)
The material was fabricated using dual material 3D printing. Polylactic acid (PLA) was used for rigid components, while thermoplastic polyurethane (TPU) provided flexible hinges. The hinges were designed with reinforced interfaces to prevent failure under repeated bending. These composite hinges showed 46 percent higher tensile strength than hinges made of TPU alone and maintained mechanical performance over 10,000 loading cycles. Across these tests, stiffness degraded by less than six percent, and energy dissipation remained nearly constant.
Beyond single units, the researchers built assemblies composed of multiple FTM modules. These multicell structures showed consistent behavior regardless of which part of the structure was loaded. Tests confirmed that the material exhibits a negative Poisson’s ratio close to minus one, meaning it contracts laterally when compressed vertically. This auxetic response helps distribute forces evenly and enhances resistance to localized deformation.
One of the key advantages of the system is that its mechanical behavior can be programmed through changes to geometry rather than composition. Adjusting the curvature of rods, the length of cables, or the angles between elements tunes the stiffness and energy absorption characteristics. Shorter cables increase initial stiffness by introducing pretension. Longer rods enable more energy to be absorbed before the structure reaches its limit. Inclined rods modify the balance between twist and compression, allowing the designer to control how deformation unfolds under load.
The structure also performs well under impact. Drop tests showed that the metamaterial reduced peak impact forces by up to 40 percent compared to a rigid surface. In indentation tests, the material distributed localized forces across multiple cells. The system recovered its original shape in about 70 milliseconds after impact. When struck at the center of a nine cell array, the structure exhibited the highest load capacity, demonstrating that neighboring units actively reinforced the affected area. This cooperative behavior enhanced the effective strength of the material by up to 47 percent compared to single unit tests.
These results suggest that the combination of twist compression coupling, elastic recovery, and structural programmability could be useful in areas where repeated loading is unavoidable. In wearable protective systems, the ability to absorb and dissipate energy without permanent deformation would reduce the need for replacement and improve comfort. In soft robotics, this kind of structural intelligence could enable machines that change shape smoothly and recover quickly. In aerospace systems, where both weight and resilience are critical, the material’s high energy absorption and fast recovery may offer advantages over traditional damping systems.
Importantly, the geometry here does not just support the structure. It defines its behavior. The modular design allows for tuning without redesigning the entire system. By building mechanical function directly into the form of the material, the authors demonstrate how tensegrity principles and biologically inspired geometry can be used to create responsive, reusable structures with properties that emerge from their shape rather than their substance.
The study marks a significant step toward materials that do more than passively resist force. Through careful structural design, it becomes possible to guide how energy moves through a material, how deformation happens, and how recovery proceeds. This approach blurs the line between structure and mechanism, offering a path to materials that are not just strong or flexible, but actively programmable in how they respond to the world around them.
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