A fabrication method for creating programmable monolithic soft robotic actuators using bubble casting techniques

Background

Soft robotics is an emerging field that draws inspiration from biological organisms to create machines capable of flexible, adaptive, and lifelike movements. Unlike traditional rigid robots, soft robots are constructed from compliant materials such as elastomers, allowing them to safely interact with humans and delicate objects, navigate complex environments, and perform tasks that require gentle manipulation. The demand for soft robots is rapidly increasing in applications ranging from biomedical devices and wearable technologies to industrial automation and search-and-rescue operations. However, realizing the full potential of soft robotics hinges on the development of fabrication methods that can produce actuators with complex, programmable motions, high robustness, and scalability.

Current manufacturing approaches for soft robotic actuators—such as molding, rapid prototyping, film coating, and 3D printing—face significant limitations. These methods often require the assembly or bonding of multiple parts, which introduces potential points of failure and limits the achievable geometries and aspect ratios. Design flexibility is constrained by the need for precise machining or layer-by-layer construction, making it challenging to produce actuators with intricate internal structures or customized mechanical responses. Scalability is another major hurdle, as traditional techniques are labor-intensive and difficult to adapt for high-throughput or continuous production. As a result, existing soft actuators may suffer from defects, inconsistent performance, and limited functionality, impeding the broader adoption of soft robotics in demanding real-world applications.

Technology

This technology introduces a novel fabrication method for soft robotic actuators, known as “bubble casting.” The process involves injecting a bubble into a mold filled with a liquid elastomer that is in the process of solidifying. As the bubble moves through the elastomer, it carves out a central cavity, and the interplay of viscous, capillary, and gravitational forces during drainage creates a membrane with an asymmetric thickness profile. This asymmetry is key: when the actuator is later inflated, the thinner membrane sections expand more than the thicker base, resulting in predictable morphing behaviors such as curling, coiling, or sequential motion. The mechanical response of each actuator can be precisely programmed by adjusting parameters like bubble velocity and drainage duration, allowing for the creation of monolithic, high-aspect-ratio soft robots that perform complex tasks from a single pressure source—without the need for assembly or bonding of multiple parts.

What differentiates this technology is its robust, scalable, and programmable approach to soft actuator fabrication, overcoming major limitations of traditional methods such as molding, 3D printing, or rapid prototyping. Unlike conventional techniques that often require assembling multiple components, this method produces defect-free, single-piece actuators with customizable geometry and motion, all governed by fluid mechanics rather than precision machining. The process supports both batch and continuous manufacturing, is adaptable to various curable materials, and enables fine-tuning of actuator properties through simple control of process parameters. This results in actuators with predictable, programmable mechanical responses—validated by theoretical modeling and experimental data—making the technology highly versatile for applications in soft robotics, biomedical devices, and programmable materials, and setting it apart as a significant advancement in the field.

Benefits

• Enables fabrication of monolithic, defect-free soft pneumatic actuators without assembly or bonding, enhancing robustness and reliability.
• Allows precise programming of actuator shape and mechanical response through control of bubble velocity and drainage timing, enabling complex motions like curling, coiling, and sequential actuation.
• Supports scalable manufacturing methods, including batch and continuous processes, with tunable actuator size and membrane thickness.
• Utilizes fluid-mechanics-based fabrication governed by viscous, capillary, and gravitational forces, reducing dependence on precision machining or complex tooling.
• Produces high-aspect-ratio soft robots capable of complex 3D morphing and muscle-like contractions from a single pressure source.
• Compatible with various curable elastomer materials, demonstrated with vinyl polysiloxane elastomers, allowing material flexibility.
• Validated by theoretical modeling and experimental testing, ensuring predictable and programmable actuator performance.
• Applicable to diverse fields including soft robotic manipulators, artificial muscles, biomedical devices, and programmable materials.

Applications

• Soft robotic surgical tools
• Programmable robotic grippers
• Artificial muscle actuators
• Adaptive biomedical devices
• Customizable soft robotic manipulators

Additional info

This methodology fabricates monolithic pneumatic actuators by injecting bubbles into liquid elastomer-filled molds. Interfacial flows—governed by viscous, capillary, and gravitational forces—sculpt asymmetric membrane thicknesses during drainage. Upon pressurization, thinner sections expand preferentially, inducing predictable morphing like coiling. By modulating bubble velocity and drainage duration, the mechanical response is programmed, enabling complex, high-aspect-ratio soft robotic motions from a single pressure source without requiring assembly or bonding.