From Micro Lattices to Macro Bodies: How 3D Printing Shapes the "Muscles" and "Skeletons" of Next‑Generation Humanoid Robots

In the pursuit of anthropomorphic design and high performance for humanoid robots, we have previously explored multiple challenges ranging from post-processing of TPU materials to computing power and energy supply for future robots. One core solution to tackle these challenges lies in a sophisticated structure — the lattice structure. It is the secret behind robots’ combined rigidity and flexibility, and its manufacturing method directly defines the performance ceiling of robotic devices. This article focuses on two core topics: the applications of lattice structures in robots, and the pros and cons of the two mainstream manufacturing technologies for lattice structures — vat photopolymerization and powder bed fusion printing.

Figure: Schematic of 3D printing applications in humanoid robots

I. Lattice Structures: Bionic Ingenuity for Humanoid Robots

Why are lattice structures indispensable for next-generation humanoid robots? The answer draws inspiration from nature. The efficient locomotion of living creatures relies on a seamless, gradual transition of stiffness and strength across rigid bones, soft muscles and tendons. Traditional robots are assembled from discrete rigid components, which can hardly replicate such integrated coordination.

By programming the shape, density and arrangement of unit cells, lattice structures enable continuous gradient changes from ultra-soft elasticity to high-load rigidity within a single part or material.

1. Bionic Muscles & Flexible Actuators

This is the most intuitive application of lattice structures. For instance, researchers at the École Polytechnique Fédérale de Lausanne (EPFL) developed an elephant robot using programmable foam lattices. Its trunk can twist and bend just like a real elephant’s trunk, while joints such as hips, knees and feet are engineered with higher rigidity, perfectly mimicking the tissue distribution of living organisms.In China, XPeng Motors’ IRON humanoid robot also adopts 3D-printed lattice materials to precisely replicate the lines of human muscles.

Figure: XPENG humanoid robot with lattice filling

2. Lightweight Structures & Integrated Joints

Acting as an intelligent porous material, lattices remove material from non-load-bearing areas while retaining strength at critical positions, achieving extreme lightweighting. The knee joint support of Tesla Optimus Gen2 uses 3D-printed titanium alloy lattices, cutting weight by up to 42%.

More importantly, lattice structures support functional integration. Components including bearing seats, wiring ducts and heat dissipation channels can be printed as a single piece with load-bearing structures, which reduces assembly work and improves reliability and precision.

Table: 3D printing applications on Optimus Gen 2

3. Shock Absorption, Heat Dissipation & Energy Recuperation

The honeycomb-like porous nature of lattices makes them excellent impact absorbers. Installed at joint limiters, they replace harsh metal-on-metal collisions and enable safer, smoother robot movements. Meanwhile, their large specific surface area delivers natural heat dissipation performance. Combined with high thermal conductivity fillers, lattices effectively lower the operating temperature of joint motors.Advanced TPU lattice materials can also store and release kinetic energy during compression and rebound, boosting locomotion efficiency.

Figure: Some common elastomeric lattice structures

Core Advantages of Lattice Structures:

Gradient stiffness: Enables smooth transition between rigidity and flexibility

• Extreme lightweighting: Weight reduction of over 40%

• Functional integration: Combines structural support, heat dissipation and wiring channels in one component

• Energy management: Capable of shock absorption, heat dissipation and energy recuperation

• II. Vat Photopolymerization vs. Powder Bed Fusion: Two Technical Paths for Lattice Fabrication

• High-precision 3D printing technologies are essential for manufacturing intricate lattice structures. Two mainstream processes stand out: vat photopolymerization (represented by DLP and SLA) and powder bed fusion (SLS is primarily used for TPU printing). A detailed comparison is as follows:

• Comparison Dimension	Vat Photopolymerization 3D Printing	Powder Bed Fusion (SLS) 3D Printing
  Working Principle	UV laser or planar light irradiates liquid photosensitive resin to cure parts layer by layer.	A laser selectively sinters polymer powder (e.g., TPU) to fuse particles and build parts layer by layer.
  Printing Precision	Extremely high. Industrial-grade equipment achieves micron-level precision (as low as 2.8 μm), ideal for ultra-fine lattice features and smooth surfaces.	Good. Precision typically ranges from 0.1 mm to 0.2 mm, sufficient for most functional lattice structures.
  Material Performance	Uses photosensitive resin. Its flexibility and weather resistance are slightly inferior to conventional TPU. Emerging elastomer resins are narrowing this performance gap.	Core strength. Directly uses flexible TPU powder. Finished parts deliver outstanding elasticity and weather resistance, matching the mechanical properties required for robotic "muscles".
  Design Freedom	Extremely high for complex lattices. Drainage holes must be reserved for hollow or enclosed structures to prevent residual uncured resin.	Extremely high with no need for support structures. Unsintered powder acts as natural support, enabling the production of arbitrarily complex, embedded and interlocking lattices with minimal design constraints.
  Post-Processing	Requires cleaning, support removal and secondary curing to stabilize performance. The workflow is relatively complicated.	Parts are extracted from powder and cleaned of loose powder (a common "powder residue" issue). Surfaces tend to have a granular texture; additional processing is required for a smooth finish. We offer dedicated solutions for powder removal and surface smoothing.
  Production Speed	Fast. Planar exposure technologies (e.g., DLP) cure an entire cross-section at once, 20 to 100 times faster than traditional point-by-point scanning.	Relatively slow. The laser scans point by point, and the repeated powder spreading, heating and cooling cycles extend production time.
  Environmental Friendliness	Materials are mostly thermosetting resins and non-recyclable. New-generation resins contain partial bio-based ingredients.	Materials are thermoplastics and fully recyclable.
  Cost Characteristics	Moderate equipment and resin costs. Fast single-part printing speed, suitable for small-batch production of high-precision complex components.	High equipment cost, yet high material utilization rate. Most unsintered powder can be reused, making it ideal for small-batch custom production of functional parts.

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• How to Choose the Right Technology?

• Choose Vat Photopolymerization: Prioritize this process when pursuing ultimate precision, superior surface smoothness and rapid prototyping, and when advanced elastomer resins can meet performance requirements. Typical applications include exposed flexible robotic skin with fine textures and sensor housings.

• Choose Powder Bed Fusion (SLS): Opt for SLS when part functionality and long-term mechanical performance (flexibility and durability) are top priorities, or when producing highly complex support-free structures. Typical applications include core joint bumpers and bionic muscle actuator bodies that undergo repeated bending and impact.

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III. Integration & Future: From Printed Components to Synthetic Robotic Bodies

The two manufacturing technologies are not mutually exclusive; they are evolving toward integration. On one hand, vat photopolymerization resins are becoming more durable and functionally capable. On the other hand, SLS processes are advancing in precision and efficiency, and improved post-processing delivers better surface quality. Both technologies share a common goal: transforming robot manufacturing from component assembly to integrated structure generation.

In the future, AI-driven design will enable customized performance distribution across lattice structures. Fueled by the computing revolution brought by AI Data Centers (AIDC), the simulation and optimization of complex lattices will become far more efficient. Ultimately, 3D printing will evolve from a mere manufacturing tool into an intelligent system. Starting from microscopic lattice design, it will directly fabricate macroscopic, rigid-flexible coupled robotic bodies, paving the way for practical, low-cost and high-performance humanoid robots.

This exploration spanning microscopic material processing, macroscopic energy supply and core structural manufacturing outlines the full technological evolution roadmap for humanoid robots. As a critical connecting link, lattice structures are quietly reshaping the form of next-generation mechanical life.