Lightweight Robotics and Multimaterial 3D Printing: How to Build a Soft Humanoid

Lightweight Robotics and Multimaterial 3D Printing: How to Build a Soft Humanoid

The production of lightweight and flexible robots is entering the industrial era thanks to innovative 3D printing techniques that integrate rigid and soft materials in a single process.

Soft robotics represents one of the most promising frontiers of modern automation, offering safer and more adaptable solutions than traditional rigid systems. At the heart of this revolution is a multimaterial 3D printing process developed at Harvard University, which makes it possible to create flexible robotic structures with programmed movements, eliminating the need for molds and drastically accelerating prototyping times.

Introduction to Soft Robotics and the Advantages of Lightweight

Soft robotics represents a breakthrough compared to traditional rigid systems, offering greater safety and adaptability, especially in human contexts.

Soft robots stand out from their rigid predecessors for their ability to deform, adapt, and interact safely with humans. This characteristic makes them ideal for medical applications, personal assistance, and environments where human-machine collaboration is essential. The soft robotics sector is still predominantly in the pure research phase, but the research and development landscape has begun to produce examples of early-stage commercialization.

Researchers have begun to focus on the genuine advantages of soft robotics over their more rigid counterparts, and the open design capabilities of additive manufacturing have been fundamental to this evolution. The lightness of 3D-printed components, combined with the flexibility of soft materials, makes it possible to create robotic systems that consume less energy and present lower risks in the event of accidental contact.

Multimaterial 3D Printing Technology

Multimaterial 3D printing enables the direct integration of rigid and soft components, opening new possibilities for complex and functional structures.

Multimaterial 3D printing eliminates the limitations of single-material printing or traditional casting, allowing designers to incorporate actuation pathways, graded stiffness, and functional features without additional assembly. This technology combines soft elastomers and stiffer polymers in a single build, overcoming the material integration limitations typical of conventional methods.

The process makes it possible to deposit multiple materials through a single nozzle along a precise path, with the ability to rapidly change material and create both simple and highly complex shapes. This ability to build parts directly from digital designs eliminates assembly bottlenecks, reduces delivery times, and makes it possible to incorporate pneumatic channels and other functional elements during printing itself.

The multimaterial approach solves one of the most intractable problems associated with design for the robotics industry: the creation of joints, articulations, and organic shapes that would otherwise require molds and multi-stage processes.

Harvard's Innovative Process: Rotating Head and Programmatic Inflation

The system developed by the Wyss Institute combines mechanical precision and morphological programmability through a rotating head and inflation-responsive materials.

The process developed by researchers at Harvard's School of Engineering and Applied Sciences is based on a rotating printer with a multimaterial nozzle. Users first print a rigid polymer shell, then layer a gel-like polymer on top, creating a channel when the shell fully hardens, after which the softer substance is washed away.

Once the final product is inflated, the embedded design (“programmed shapes”) fully emerges, producing bio-inspired shapes whose production would otherwise require casts and molds. As Jackson Wilt, a graduate student who worked on the project, explains: “We use two materials from a single outlet, which can be rotated to program the direction in which the robot bends when inflated. In this work, we don't have a mold. We print the structures, program them rapidly, and are able to quickly customize the actuation.”

The process involves designing an internal channel made of poloxamer, a polymer commonly used in hair gels. By adjusting the 3D printer's nozzle, its rotation speed, and the material flow rate, the researchers were able to precisely control the shape, size, and orientation of each channel. The structure is then coated with a polyurethane membrane. Once solidified, the internal poloxamer core is removed, yielding a hollow shell that can be pressurized to bend into different shapes.

This rotational movement not only enables rapid material changes, but also makes it possible to create complex geometries without the use of traditional molds. The researchers completed their work in the laboratory of Jennifer Lewis, the Hansjorg Wyss Professor of Biologically Inspired Engineering at SEAS, who was the lead author of the first study based on the underlying process, published in 2022. That earlier project demonstrated how helical shapes could be exploited to create joints and hinges for soft robotics.

Materials and Geometries: Gel-Like Polymers and Bioinspired Structures

The use of hybrid polymers allows the creation of joints and curved surfaces without supports, reducing weight and design complexity.

The choice of materials is crucial for the success of 3D-printed soft robotics. Harvard's process uses a combination of polyurethane for the rigid outer layer and poloxamer for the gel-like inner core. This combination makes it possible to obtain complex geometries with precise internal channels that, once pressurized with air, allow controlled and predictable movements.

The channels can be arranged in linear configurations as well as in flat or elevated patterns. By adjusting parameters such as nozzle geometry, rotation speed, and material flow rate, researchers controlled the dimensions, orientation, and geometry of each internal channel with high precision. This level of control makes it possible to create structures that contract, grasp objects, or expand in response to pressurization.

To demonstrate the versatility of the approach, the team 3D-printed a flower-like design in a spiral as a continuous maze-style path. They also created a five-finger handle with articulated sections that function similarly to knuckles, capable of bending in a controlled manner. Some of the example patterns detailed in the Advanced Materials article include flowers and human hands, addressing one of the most intractable problems associated with design for the robotics industry.

The combination of rigid and gel-like polymers makes it possible to obtain complex geometries without the use of traditional molds, significantly reducing the overall weight of the robotic system and simplifying design. This approach solves critical problems in lightweight robotics, such as creating joints and bio-inspired shapes that imitate natural structures.

Practical Applications: From Prosthetics to Robotic Assistants

The advantages of lightweight and flexible design find direct application in areas such as rehabilitation and personal assistance.

The potential applications of 3D-printed soft robotics are vast and promising. According to Wilt, the results highlight how rapid fabrication techniques like this could support applications ranging from surgical robotics to human assistive technologies. Predictable movement in soft robotics has traditionally depended on complex molds and multi-stage fabrication processes, slowing design iteration and limiting customization.

The new method is set to accelerate the development of adaptive systems for surgical robotics, wearable assistive technologies, and flexible industrial automation. The ability to produce soft robotic devices with embedded and programmable movement eliminates assembly steps and enables faster prototyping, design freedom, and on-demand customization compared with conventional production.

In rehabilitation, soft robots can assist patients with reduced mobility by providing gentle and adaptable support. In personal assistance, they can help elderly people or people with disabilities in daily activities, offering safe and natural interaction. Even in the industrial sector, soft robots can manipulate fragile objects or work in confined spaces where traditional rigid robots would be inadequate.

The greatest strength for the direction that soft robotics research seems to be taking, and the greatest strength for the role of 3D printing in this research area, is the potential to maximize functional design. The logical extreme of this would be to type in a desired function and have a program respond with a design suited to the purpose, a concept that has attracted a significant amount of venture capital investment in recent years.

Conclusion

The convergence between lightweight robotics and multi-material 3D printing opens innovative scenarios for the design of safer, more efficient, and more adaptable robotic systems.

The rotating multi-material 3D printing process developed at Harvard represents a significant step forward in the production of soft robots. By eliminating the need for molds, reducing prototyping times, and enabling rapid customization, this technology is transforming soft robotics from a purely research field into a sector with concrete commercialization possibilities.

Although technical and practical challenges remain before widespread adoption – including material performance, fatigue resistance, scalability for larger devices, and standardization of testing processes – the potential is undeniable. The ability to create complex structures with embedded actuation during manufacturing represents a paradigm shift in robotic design.

If advances in soft robotics can synchronize with all the progress made so far with more rigid robotic components for humanoid systems, the idea of a mass market for humanoids in the future starts to make more sense. Soft robots built with 3D printers could be a perfect use case for testing all those text-to-design applications that have attracted significant investments in recent years.

Discover how the principles illustrated can be applied to your engineering or research projects, exploring the possibilities offered by multi-material 3D printing to create robotic systems that are safer, lighter, and adaptable to the specific needs of your industry.

article written with the help of artificial intelligence systems