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Making Minimotors with Paper: Just Add Liquid

Magnetic ferropaper is an inexpensive way to make micromotors for surgical instruments. Photo courtesy of ANDREW HANCOCK/PURDUE UNIVERSITY  

Purdue University (West Lafayette, IN) researchers have developed an inexpensive way to make miniature motors and actuators using paper and liquid ferrofluid that contains magnetic nanoparticles. The resulting micromotors could be used in minimally invasive surgical instruments. 

Babak Ziaie, professor of electrical engineering at Purdue, says the process is very simple. “All you need to do is put a drop on the paper. The paper soaks it up, and there you are,” says Ziaie, adding that the appeal of the technology is the inexpensive process. The method used to create this paper doesn’t require special lab facilities either, and according to Ziaie, a high school student could make it.

The researchers first used scissors to cut the paper. However, laser machining makes shapes that are more complicated and smaller—as small as 100 μm.

The process begins by impregnating regular paper with mineral oil and iron oxide magnetic particles, which are commercially available. Ziaie recommends newspaper and soft tissue paper due to the porous nature of those materials. To provide resistance to water and fluid evaporation, the paper is coated with a biocompatible plastic film. The coating enhances the strength, stiffness, and elasticity of the paper, which is called ferropaper because of its relation to iron.

For biomedical applications, the softness of the paper is useful in cases in which a lot of force shouldn’t be applied, such as for tissue cultures. And although it could be difficult to use the ferropaper to make motors for surgical instruments, it’s not impossible, says Ziaie. “[Devices] that are easier [to make] are grabbers, or small tweezers, that you can remotely activate with a magnetic field.” Such grabbers would be used to touch and manipulate sensitive tissue during a minimally invasive procedure such as an eye operation.

The researchers used the ferropaper to make a cantilever actuator, which is moved using a magnetic field. Ziaie says that although cantilever actuators are common, they’re usually made from silicon, which is much more expensive than the ferropaper and requires a special facility for the manufacturing process.

The next step is to create an easier way to integrate the ferropaper into a substrate. “If you want [the ferropaper] it to be more useful, you have to be able to attach or integrate it into other materials like polymers or silicones,” says Ziaie.

The researchers are currently working on licensing the technology to a company. At press time, they were filing for patent protection. They presented their research at the 23rd IEEE International MEMS conference in Hong Kong.

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