Intelligent Multifunctional Materials Are the Future of Soft Robotics
Wed, April 21, 2021

Intelligent Multifunctional Materials Are the Future of Soft Robotics

Soft robots can provide in-home assistance by moving and gripping objects. / Photo by: pixelbliss via 123rf 


In factories, robots are solely used for heavy lifting or fine detail work, according to Michael Ford of the news platform The Conversation. Currently, Boston Dynamics’ nimble four-legged robot, Spot, is available for lease to companies. The robot can undertake different real-world jobs. This innovation demonstrates how “common interactions between humans and machines have become” recently. 

But it’s not only brawny robots that are being developed today. Many researchers conclude that soft robots are capable of safe physical interaction with humans, per the findings of Carmel Majidi of publishing firm Wiley Online Library and Steven I. Rich and colleagues of academic portal Nature. For example, soft robots can provide in-home assistance by moving and gripping objects. Soft robots will populate the future along with hard robots. 

What Is Soft Robotics? 

It is an emerging field of research where a robot’s body is composed of flexible and soft materials, said Hayato Saigo and colleagues of research portal Hindawi. In their journal article titled “Analysis of Soft Robotics Based on the Concept of Category of Mobility,” the robot’s body allows it to bend, deform, and twist to “move or adapt to the environment for grasping.” This is difficult or even impossible to achieve for hard robots with rigid bodies. 

The field is being intensively studied to address the difficulties of traditional hard robots built “from a rigid underlying structure.” Soft robotics is also studied to create new value by utilizing intrinsically soft and/or extensible material. Hard robots require precision control of their actuators for links and joints. 

They perform well for executing repetitive, well-defined motions, making them suitable for manufacturing. However, hard robots have difficulty in dealing with uncertain environments. Interestingly, soft robotics is inspired by biology, specifically the skin sensors, muscle-tendon complex, and retina of living organisms.  

The Future of Soft Robotics

Soft robotics and wearable computers are technologies that are safe for human interaction. These two technologies will demand new types of materials. The components should be soft and stretchable, allowing the robot to perform various functions. Ford and his colleagues at the Soft Machines Lab at Carnegie Mellon University developed multifunctional materials. Along with their collaborators, Ford and his team created a material that can combine the properties of soft rubbers, metals, and shape-memory materials.  

These multifunctional materials can heal themselves, conduct electricity, and detect damage. They are also capable of sensing touch and changing their shape and stiffness in response to electrical stimulation akin to an artificial muscle. Pioneering researchers Kaushik Bhattacharya and Richard James described them as “the material is the machine.”


Soft robotics and wearable computers are technologies that are safe for human interaction. / Photo by: Oleg Doroshin via 123rf


Making Multifunctional Materials Intelligent

The idea of the material is the machine can be encapsulated in embodied intelligence. Embodied intelligence is used on a system of interconnected materials, similar to tendons in your knees. When you run, for instance, the tendons can stretch and relax to adapt as soon as your foot lands on the ground. This process doesn’t need any neural control. 

You could also think of embodied intelligence as a single material that can process, sense, and respond to its surroundings without sensors, processing units, and other embedded electronic devices. One good example is rubber. It is composed of strings of coiled and linked molecules. Stretching or compressing the material uncoils the strings, but the links force the rubber to return to its original position. 

Engineered materials suitable for machine-human interaction will require multifunctionality in the near future. Recently, Ford and his co-workers created self-healing circuits, embedding them in rubber. The circuits dispersed micro-scale liquid metal droplets enclosed in an electrically insulating “skin” through the rubber. In the rubber’s original state, the thin metal oxide layer of the skin stops it from conducting electricity. 

If enough force is applied to the metal-embedded rubber, the droplets will rupture and form electrically conductive pathways. Hence, the lines printed in the rubber become self-healing. Alternatively, shape memory is also a notable example of embodied intelligence in materials. Shape memory materials are great for linear motion in soft robotics as they can move back and forth, similar to your bicep muscle. 

Hillel Aharoni and colleagues of the Proceedings of the National Academy of Sciences of the United States of America (PNAS), a peer-reviewed journal platform, used a class of materials called liquid crystal elastomers to transform a flat rubber-like sheet into a 3D topographical map of a person’s face. 

A New Innovation

Ford and his colleagues created a soft composite with unprecedented multifunctionality. It is soft and stretchable. It can also conduct heat and electricity, unlike regular rubber. What makes the soft composite stand out is its ability to actively change its shape. It is also resilient to damage. Their soft composite is capable of self-healing as well as detecting damage in a “whole new way.” 

Damage helps it form new electrically conductive lines, which trigger its shape-morphing capabilities. When punctured, the composite responds by spontaneously contracting. This is not mere fantasy. We have to accept that shape-morphing composites are starting to make a mark in the world. These composites may be applicable to soft assistive devices like companion robots, prosthetics, antennas, and more. 

The soft robotics field will be highly dependent on materials that can self-heal, morph, and detect damage. These materials are paving the way for the future of soft robotics. We will get to see them in action outside of research labs someday.