Information magazine of the Department of Industrial Engineering
Università di Trento
Information magazine of the Department of Industrial Engineering
Università di Trento
In our daily lives, robots are silent companions, present in factories, homes, and even hospitals. From robust and powerful industrial robots to small household assistants, robotics technology is constantly evolving to meet diverse human needs. So, what will be the next revolution? The so-called soft robotics. This approach to robotics aims to transform rigid robots into flexible and adaptable tools capable of safely interacting with their surroundings. Soft robots are ideal for operating in unstructured environments and handling objects and living beings delicately.
In the field of soft robotics, one of the most critical and fascinating aspects is the development of artificial “muscles”, actuators that enable flexible robots to move, adapt, and interact with the world, much like biological muscles. But why is this such a complex challenge?
Think about human muscles—they are incredibly efficient, capable of contracting up to 20% of their resting length and generating power up to 50 W per kilogram of muscle mass. Reproducing these performances with artificial materials is anything but simple. However, achieving this would unlock new levels of functionality and versatility in soft robotics.
Conventional motors, based on rigid components like magnets, bearings, and metal casings, are designed for high-speed rotations and are optimized for slow, linear movements. However, soft robotics requires flexibility and the ability to adapt to more complex interactions and movements.
This is why smart materials offer a particularly promising solution for the development of robotic artificial muscles. These materials have the unique ability to respond to external stimuli, such as electric currents, temperature changes, or light radiation, by deforming—just as our skeletal muscles contract in response to electrical impulses from the brain.
Giacomo Moretti’s research focuses on the design, modeling, and experimental demonstration of robotic artificial muscles using smart polymeric materials. Over the years, he has explored various principles and materials to develop polymeric robotic muscles, enabling the creation of increasingly compact, fast, and lightweight soft robots.
“During my Ph.D. at the Scuola Sant’Anna in Pisa, I started working with thermoactive polymers. The idea—originally developed by a research group at the University of Dallas—is simple: by twisting highly drawn polymer fibers (such as common fishing lines or sewing threads made of nylon), it is possible to obtain spring-like structures that contract when heated (Figure 1). However, these muscles have a major limitation: their slow response time, as they require significant time to heat up and cool down,” says Moretti.
“Later, I shifted my focus to electroactive polymers (activated by an electric current), specifically dielectric elastomers. These materials can stretch when electrically stimulated. I pursued this research further during a period at the Saarland University in Germany, where we developed fast and repeatable dielectric elastomer muscles based on rolled polymer membranes (Figure 2), which closely resemble the structure of biological muscles.”
However, dielectric elastomers have limitations in contraction due to their inherent stiffness. To overcome this challenge, in 2020, Professor Moretti collaborated with colleagues from the Department (Professors Fontana, Fambri, and Diré) to develop a new type of muscle, based on a similar principle but using different materials and structures.
These new muscles feature a bellows-like structure (Figure 3), with polymeric walls and an insulating fluid inside. By applying electric charges to the external surfaces of the polymer, the fluid is expelled, allowing the muscle to contract significantly with minimal resistance. These muscles can achieve contractions of up to 40% of their original length (several centimeters) and lift considerable loads (up to several hundred grams) while remaining extremely lightweight.
“In summary, my research has explored and developed various artificial muscle solutions, from thermoactive polymers to dielectric elastomers, and finally, to bellows-structured muscles. These advances represent significant steps forward in soft robotics, bringing us ever closer to the creation of flexible and powerful robots with performance comparable to biological muscles.”
This innovative approach to artificial muscles, combining fluids and polymers, has attracted the attention of the scientific community. This concept is seen as a potential breakthrough in soft robotics, promising the development of flexible robots with previously unimaginable performance.
Driven by this vision, Moretti and his team are focusing on designing complex robots based on the artificial muscles they have developed. At the same time, they are exploring new application opportunities, particularly in the aerospace sector. This industry constantly seeks lightweight and compact actuation solutions, which align perfectly with the characteristics of the systems the team is developing.
Through these efforts, their goal is to advance technological innovation and expand the potential applications of robotics, pushing the boundaries of what flexible robots can achieve.
