Predictable motion in soft robotics has traditionally depended on complex molds and multi-step fabrication processes, slowing design iteration and limiting customization. Researchers at Harvard University have now introduced a multimaterial 3D printing approach that embeds actuation directly into flexible structures during fabrication, allowing soft robotic devices to be produced with built-in, programmable movement.
Reported in Advanced Materials, the method uses additive manufacturing to create filament-based components with precisely engineered internal channels that enable controlled bending and deformation when pressurized with air, eliminating assembly steps and allowing faster prototyping, design freedom, and on-demand customization compared to conventional manufacturing. The new method is expected to accelerate the development of adaptive systems for surgical robotics, wearable assistive technologies, and flexible industrial automation.
The study was conducted by graduate student Jackson Wilt and former postdoctoral researcher Natalie Larson in Jennifer Lewis’s lab at Harvard SEAS, with support from the U.S. National Science Foundation and the Army Research Office’s Multidisciplinary University Research Initiative (ARO MURI).
Rotational Multimaterial 3D Printing Approach
The fabrication method builds on a technology known as rotational multimaterial 3D printing, previously developed in the Lewis laboratory. This technique uses a single nozzle capable of depositing multiple materials at once. As the printing system rotates and shifts orientation, it deposits material in customizable configurations. Earlier work from the group used this strategy to create helical soft structures that function as artificial muscles and other adaptive components.
In the new study, the team produced filaments featuring a polyurethane outer layer combined with an internal channel formed from a poloxamer polymer commonly used in hair gels. These filaments could be arranged in linear configurations as well as flat or elevated patterns. By adjusting parameters such as nozzle geometry, rotational speed, and material flow rate, the researchers controlled the size, orientation, and geometry of each internal channel with high precision.
“We use two materials from a single outlet, which can be rotated to program the direction the robot bends when inflated,” Wilt said. “Our goals are aligned with creating soft, bio-inspired robots for various applications.”
After the outer shell hardened, the poloxamer core was removed through a washing process, leaving behind tubular structures with hollow interiors. These channels can be pressurized to enable directional bending, allowing the resulting devices to expand, contract, or grasp objects.
Streamlined Fabrication Without Molds
The technique introduces a simplified pathway for producing mechanically complex soft robotic systems. Conventional fabrication typically involves molding elastomeric materials, embedding pneumatic pathways onto surfaces, and sealing them beneath additional layers, a process that can be time-consuming and difficult to customize.
“In this work, we don’t have a mold. We print the structures, we program them rapidly, and we’re able to quickly customize actuation,” Wilt said.
To demonstrate the versatility of the approach, the team spiral-printed a flower-like design in a continuous, labyrinth-style path. They also created a five-fingered handle featuring jointed sections that function similarly to knuckles, capable of controlled bending. According to Wilt, the findings highlight how rapid fabrication techniques like this could support applications spanning surgical robotics and human assistive technologies.
Limitations and Technical Challenges
Despite its potential, the multimaterial 3D printing approach still faces several technical and practical challenges before widespread adoption. Material performance remains a key consideration, as soft robotic components must balance flexibility with durability, fatigue resistance, and long-term mechanical stability under repeated pressurization cycles. Scaling the process for larger devices or high-throughput manufacturing may also introduce complexities related to print consistency, internal channel reliability, and quality control.
As with many emerging additive manufacturing techniques, further work is needed to validate repeatability, refine material combinations, and establish standardized testing and certification pathways, particularly for safety-critical applications such as surgical robotics.
Multimaterial 3D Printing Enables Programmable Soft Robots
Soft robotics has long been constrained by fabrication limits: traditional molding and multi-step assembly slow iteration and make precise, predictable motion difficult. Additive manufacturing overcomes these hurdles by building parts directly from digital designs, eliminating assembly bottlenecks, cutting lead times, and allowing pneumatic channels and other functional elements to be embedded during printing. This enables soft robots with reliable, programmable motion for applications such as surgical robotics and wearable assistive devices.
Multimaterial 3D printing takes this further by combining materials, soft elastomers and stiffer polymers, in a single build. This removes the material integration limits of single-material printing or casting, allowing designers to embed actuation pathways, graded stiffness, and functional features without extra assembly.
Recent examples highlight the practical impact of multimaterial 3D printing. Harvard’s MM3D method printed soft robots with multiple materials and embedded channels, creating origami-like walkers that carry several times their own weight. In addition, CU Boulder researchers developed OpenVCAD, a tool for smarter multimaterial 3D design. These examples demonstrate the impact of multimaterial additive manufacturing and confirm it as a practical method for producing programmable soft robotic systems.
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Featured image shows Print-path planning for generating complex soft robotic matter. Image via Harvard.
