Robots are traditionally built from rigid materials such as metal, plastic, gears, hinges and bolts. These components are useful for precise mechanical tasks, but they can make robots less flexible when they need to move through complicated environments or interact gently with people and delicate objects.
Nature uses a very different strategy. Animals and plants can bend, stretch, twist and change their shapes continuously without relying on conventional mechanical joints. Inspired by these natural movements, researchers led by Jones have developed a new approach to creating soft robots from flexible elastomer materials. Their method combines advanced fabrication, bubble-based structures and pneumatic actuation to produce complex robotic movements from a single integrated structure.
The technology could eventually help create artificial muscles, adaptive robotic grippers and highly complex soft machines.
What Makes Soft Robots Different?
Soft robotics focuses on building machines that can deform and move using flexible materials. Instead of relying entirely on rigid joints, soft robots use elastomers—rubber-like materials capable of stretching and changing shape.
A key component is the soft actuator. An actuator converts an external stimulus into movement. In pneumatic soft robots, air pressure is commonly used. When air enters an internal chamber, the chamber expands, causing the surrounding elastomer to bend, stretch or twist.
This simple principle can create surprisingly sophisticated movements.
For example, a soft gripper can wrap around an irregular object rather than grabbing it with rigid fingers. An artificial muscle can contract or bend when pressure is applied, producing movements that resemble biological tissues.
The Challenge of Manufacturing Soft Robots
Although soft robots have many advantages, manufacturing complicated actuators remains difficult.
Many existing approaches require several individual components to be fabricated separately and then assembled. Modern rapid-prototyping techniques have made this process easier, but they still have limitations involving scalability, design flexibility and robustness.
The more components a robot contains, the more complicated its assembly becomes. Connections between individual pieces can also become potential weak points.
The researchers therefore developed an all-in-one approach in which fabrication and movement programming are closely connected.
Instead of simply assembling separate robotic parts, the technique uses controlled flows of elastomer materials and bubble-like internal structures to create integrated pneumatic actuators.
How Does Bubble Injection Help?
One important aspect of the fabrication concept is the use of bubble injection to create internal air-filled structures within the soft elastomer.
These bubbles are not simply loose bubbles floating inside the robot. Instead, the fabrication process creates controlled cavities or channels that become part of the actuator's internal architecture.
Once the elastomer cures, these internal structures can function as pneumatic chambers. When air pressure is introduced, the chambers expand and push against the surrounding flexible material.
That deformation produces movement.
In simple terms: bubble injection helps create the internal chambers, and controlled air pressure later makes those chambers deform the soft robot.
This provides engineers with another way to control how different sections of a soft actuator respond to pressure.
Turning Shape Into Movement
One of the most interesting features of the researchers' approach is that movement can be programmed into the geometry of the actuator.
The internal chambers do not necessarily have to be identical. Their size, shape, position and arrangement can be carefully designed.
When pressure is applied, different regions can therefore deform in different ways.
For example, one section might bend more strongly than another. A long actuator could curve progressively along its length. Multiple sections could also move one after another.
This means the physical structure itself can contain information about how the robot should move.
Instead of depending entirely on complicated electronics, motors and software, some of the robot's behavior is effectively built into its material and geometry.
How Can One Input Produce Several Movements?
The researchers demonstrated an especially interesting capability: sequential motion generated from a monotonic stimulus.
A monotonic stimulus is an input that continuously increases or decreases rather than repeatedly changing direction.
Imagine gradually increasing air pressure inside a soft robotic structure. Instead of every section moving at the same time, the carefully designed geometry can cause one section to deform first, followed by another and then another.
The result is a sequence of movements produced from a relatively simple input.
This could make future soft robots easier to control because sophisticated motion does not always require sophisticated external control systems.
Understanding the Fluid Mechanics
The researchers did not rely only on trial and error. They studied the fluid mechanics involved when the elastomer materials flow during fabrication.
Understanding these flows is important because the way the material moves determines the final structure.
The team developed models that describe how the actuator forms and how it subsequently changes shape when stimulated.
This creates a predictive design process.
Instead of manufacturing an actuator and repeatedly testing different versions, engineers could potentially use mathematical models to determine the geometry required for a particular movement before fabrication.
That could significantly speed up the development of customized soft machines.
Applications in Artificial Muscles
One promising application is the development of artificial muscles.
Biological muscles produce movement by changing their shape and generating forces. Soft pneumatic actuators can perform somewhat similar functions by expanding, contracting or bending when pressure changes.
Because the new fabrication method allows the internal structure to be customized, engineers could design actuators for specific movement patterns.
Such artificial muscles could eventually become useful in wearable technologies, assistive devices and robotic systems that require flexible movement.
Smarter and Gentler Robotic Grippers
Soft robotic grippers are another major application.
Rigid robotic hands can be excellent at repetitive industrial tasks, but they may require precise positioning to avoid damaging fragile objects.
Soft grippers can conform to an object's shape. Their flexibility allows them to distribute forces over a larger area.
With bubble-created pneumatic chambers and carefully programmed geometry, future grippers could potentially perform more complex gripping motions while using relatively simple pressure inputs.
This could be useful for handling delicate products, biological materials or objects with unusual shapes.
Creating Long and Winding Robots
The researchers also see opportunities for producing long, tortuous and vascular structures.
Such structures can be difficult to manufacture when they must be assembled from many separate parts.
An integrated fabrication approach could make it easier to create continuous soft structures with complicated pathways.
This opens possibilities for robots that can bend around obstacles, navigate confined spaces or follow winding paths.
The ability to combine complex geometry with flexible materials could also create robotic behaviors that would be difficult to achieve with conventional mechanical systems.
When Geometry Becomes the Robot's Intelligence
Perhaps the most important idea behind this research is that a robot's intelligence does not always have to come from electronics.
The material itself can contribute to the robot's behavior.
By carefully controlling the geometry, internal pneumatic chambers and material properties, engineers can make a soft machine respond differently to the same external stimulus.
This takes advantage of material and geometric nonlinearities, where a relatively simple input can produce complicated changes in shape.
Nature has evolved countless examples of this principle. The researchers' approach attempts to bring some of that efficiency into engineered machines.
A New Path for Soft Robotics
The combination of elastomer flows, bubble-based internal structures, pneumatic actuation and mathematical modeling could provide a new route for manufacturing advanced soft robots.
Rather than constructing complicated machines from numerous individual components, engineers may be able to create integrated actuators whose shape, material and internal air pathways are designed together.
The researchers believe the flexibility, robustness and predictive nature of this methodology could accelerate the development of soft robotics.
In the future, robots created using these principles could move more naturally, adapt to complex environments and perform sophisticated sequences of motion using surprisingly simple inputs.
The ultimate goal is not simply to make robots softer. It is to make machines that can move, deform and adapt more like living organisms. Bubble-created pneumatic structures combined with carefully programmed elastomer geometry could become an important step toward that vision.
Reference: Jones, T.J., Jambon-Puillet, E., Marthelot, J. et al. Bubble casting soft robotics. Nature 599, 229–233 (2021). https://doi.org/10.1038/s41586-021-04029-6
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