The ability to control the motion of soft robots, coupled with their flexibility, gives them potential applications ranging from biomedical technologies to manufacturing processes, researchers said.
A team of researchers from North Carolina State University (NC State) found a way of embedding long chains of nanoscale magnetite particles in sheets of elastic polymer to form a magnetic polymer nanocomposite.
By applying a magnetic field, the researchers can control the way the nanocomposite bends - making it a soft robot.
The process begins by dispersing nanoparticles of magnetite, an iron oxide, into a solvent. A polymer is then dissolved into the mixture, which is poured into a mold to form the desired shape.
A magnetic field is then applied, causing the magnetite nanoparticles to arrange themselves into parallel chains.
The solution is dried, locking the chains into place, and the finished nanocomposite can be cut, to further refine its shape.
"Using this technique, we can create large nanocomposites, in many different shapes, which can be manipulated remotely," said lead author Sumeet Mishra, a PhD student at NC State.
"The nanoparticle chains give us an enhanced response, and by controlling the strength and direction of the magnetic field, you can control the extent and direction of the movements of soft robots," Mishra said.
The researchers have also constructed a simple model to explain how the chained nanoparticles affect the mechanical response in magnetic fields.
"The key here is that the nanoparticles in the chains and their magnetic dipoles are arranged head-to-tail, with the positive end of one magnetic nanoparticle lined up with the negative end of the next, all the way down the line," said corresponding author Joe Tracy, from NC State.
"When a magnetic field is applied in any direction, the chain re-orients itself to become as parallel as possible to the magnetic field, limited only by the constraints of gravity and the elasticity of the polymer," he said.
The researchers believe this technique may be especially attractive for some biomedical applications, as compared to soft robotics that rely on electricity or light for control.
"Electrical control can raise safety issues for some medical applications," said Mishra.
"And both electrical and light signals pose challenges in terms of communicating those signals to devices embedded in the body. Magnetic fields, on the other hand, pass through easily - and pose fewer safety challenges," he said.
The study was published in the journal Nanoscale.
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