A single 3D-printed elastic lattice structure enables multi-stiffness biomimetic muscles in humanoid robots, replacing complex traditional components and simplifying design.
At the 2025 Xpeng Tech Day held on November 5th, Xpeng's new-generation humanoid robot, IRON, made its debut. Its design is highly anthropomorphic, it walks with agility, and it utilizes all-solid-state batteries. What caught the attention of 3D Printing Technology Reference was that IRON possesses "extremely compact biomimetic muscles," a departure from the hard-shell enclosures typical of most current robots. He Xiaopeng referred to it as the "most human-like humanoid robot."
From on-site videos and graphic introductions, it's understood that the biomimetic muscle effect is achieved through a lattice structure. According to a Phoenix News report, it is precisely this 3D-printed lattice material. He Xiaopeng pointed out that the sophistication of this technology lies in its ability to generate personalized 3D lattice topological structures based on different body shapes. This means IRON can possess different body curves, just like real people, ultimately enabling highly flexible production for customizing robot body shapes according to user preferences. (Special note: The use of 3D printing was not explicitly confirmed by the official.)
The field of robotics has long faced a significant challenge: how to replicate the fine control and flexible characteristics of biological muscles? Biological muscles can provide both strength and cushioning simultaneously, whereas traditional actuators often force a choice between the two. 3D-printed elastic lattice structures might become one of the solutions for 'biomimetic muscles' in humanoid robots.
Xpeng's newly released IRON humanoid robot offers a groundbreaking solution—by using an elastic lattice structure to successfully simulate the human muscular system. This biomimetic design grants the robot movement capabilities close to those of a biological organism, signaling the opening of a entirely new direction.
The advantage of lattice structures lies in their programmable mechanical properties. By adjusting the design parameters of the unit cells, engineers can precisely control the softness and hardness of the lattice modules in different directions.
Chinese scholar Guan Qinghua and others from the School of Engineering at EPFL (École Polytechnique Fédérale de Lausanne) in Switzerland recently published research titled "Lattice-structured musculoskeletal robots: Reshaping body structures using programmable geometric topology and anisotropy" as a cover article in Science Advances.
They developed a lattice structure generation technology that supports over a million discrete configurations and infinite geometric variations. Using different lattice distributions manufactured from a single material, the material can exhibit different states—soft or rigid—in different areas. 3D Printing Technology Reference notes that this scheme provides a scalable solution for designing lightweight, adaptable robots.
This characteristic of "one structure, multiple stiffnesses" enables individual voxelated muscle units to supplant conventional complex multi-component drive systems, substantially streamlining the robot's structural design.
The core of this technological leap lies in the combination of the development of special elastomer materials and advanced manufacturing processes. Thermoplastic polyurethane (TPU) elastomer has become the material of choice, as it combines the high elasticity of rubber with the strength of plastics, maintaining structural integrity even after tens of thousands of cycle tests.
Domestically in China, a very typical developer of 3D printing materials, processes, and equipment is Boli Technology. Based on an interview with Boli Technology by 3D Printing Technology Reference during the TCT event in Shenzhen, the company currently has nearly ten thousand material formulations in its overall product lineup and has introduced 3D-printed multi-layer constructed honeycomb composite materials for humanoid robots. Such materials possess multiple characteristics including high elasticity and demonstrate exceptional performance in shock absorption, lightweighting, and heat dissipation. Data shows they have high energy absorption rates and strong deformation recovery capabilities.
For manufacturing such complex internal lattice structures, traditional injection molding or cutting processes are completely inadequate. 3D printing technology has become the only feasible solution for realizing this design. Digital Light Processing (DLP) 3D printing technology, with its advantages of high precision and speed, has become the preferred process for manufacturing microscopic lattice structures. This technology builds complex lattices by curing photopolymer resin layer by layer, capable of achieving feature sizes as low as 50 micrometers.
The advantage of 3D printing technology also lies in its unparalleled design freedom—lattice type, density gradient, and unit cell size can all be precisely defined in the digital model and then realized in a single printing process.
Equipping humanoid robots with biomimetic muscles may not be a first-time achievement, but the IRON robot is a rare case where the biomimetic lattice structure is visibly evident. Although the official did not explicitly state it was manufactured using 3D printing, detailed reasoning suggests that 3D printing technology could indeed accomplish it.
Moving from the laboratory to industrialization, the application scope of elastic lattice structures is continuously expanding. With ongoing breakthroughs in materials science and continual advancements in printing processes, we are likely to witness flexible structures sharing equal importance with rigid components in the field of robotics within the next decade.
