Researchers have engineered a nanomaterial flexed by rare earth magnets that is as soft as skin but strong as steel.

The studies of robotics, biomedical engineering, and wearable technology all intersect over the immensely complex task of replicating human musculature – creating materials strong enough to replace or enhance human limbs, flexible and soft enough to manipulate delicate objects or complete precise tasks in everyday life, during space exploration or on a battlefield.

The next generation of manufacturing robotics, military exoskeletons, and medical prosthetics all require human-like artificial muscles, with groundbreaking results coming out of Ulsan National Institute of Science & Technology in South Korea.

Researchers led by Professor Hoon Eui Jeong from the Department of Mechanical Engineering have developed a magnetic composite artificial muscle that operates more like the real thing – if a bit superhuman.

This new material can adapt its stiffness, transitioning from soft to rigid, while withstanding tensile and compressive forces thousands of times its weight, with stretchability exceeding 800%.

"Despite recent advancements, artificial muscles have not yet been able to strike the right balance between exceptional mechanical properties and dexterous actuation abilities that are found in biological systems," the scientists posit in a report on their findings published in Nature Communications. "Here, we present an artificial magnetic muscle that exhibits multiple remarkable mechanical properties and demonstrates comprehensive actuating performance, surpassing those of biological muscles."

Like its fleshy equivalent, the robust nanomaterial also demonstrates strength and flexibility.

"Utilizing multi-stimulation methods, including laser heating and magnetic field control, we can remotely execute fundamental movements such as elongation, contraction, bending, and torsion, along with more complex actions like manipulating objects with precision," Professor Jeong explained.

The team also incorporated an innovative vibration-damping hydrogel layer in its prototype design, enabling unprecedented control at high speeds.

"It adeptly executes various programmable responses and performs complex tasks while minimizing mechanical vibrations," the researchers penned in the report. "Furthermore, we demonstrate that this composite muscle excels across multiple mechanical and actuation aspects compared to existing actuators."

While conventional soft materials are great for smooth movements, they fall short regarding strength and load-bearing capacity. Materials commonly tested in soft robotics and devices, such as silicones and hydrogels, have limited mechanical properties. Their inherent softness has limited resistance to fatigue or damage.

Conversely, stiffness-tunable materials are too brittle to lift heavy weights or too flexible to support controlled precision. Examples include pneumatic systems, low-melting-point and shape-memory alloys. These materials typically exhibit a narrow stiffness range and minimal load capacity. They often require wired electrical connections or exacting temperature control.

"[W]e present a reconfigurable and adaptable soft magnetic muscle that outperforms the mechanical and actuating performance of biological muscles," the researcher wrote. "These remarkable attributes are achieved by integrating a shape memory polymer and magnetic particles in a composite configuration."

For this, they used two key materials that could switch between hard and soft states – shape memory polymers embedded on the surface with ferromagnetic particles – specifically neodymium magnets.

A neodymium permanent magnet is made by alloying the rare earth element neodymium with iron and boron to produce strong magnetic properties. The ferromagnetic particles within the polymer both strengthen the muscle and respond to the magnetic fields created by the rare earth magnet, allowing the muscle to be highly adaptable and change its stiffness, all controlled remotely, rapidly, and precisely.

The prototype muscle proved incredibly efficient, converting 90.9% of the input energy into superhuman feats of strength.

"This research opens avenues for transformative applications across diverse sectors, driven by mechanical properties and performance that transcend the limitations of existing artificial muscles," Jeong concluded.