Minimalist Micrometer Robots for Medical Applications

Now, engineers at Drexel University have pioneered a new fabrication method for tiny swimmers using the minimum geometric requirements for locomotion in a fluid.

Using just two conjoined microparticles coated with magnetic iron oxide debris, the microrobots spin and move in a manner similar to bacterial flagella when exposed to an external magnetic field.

Min Jun Kim, professor of mechanical engineering and mechanics at Drexel University, and his colleagues recently discussed the concept in Applied Physics Letters.

The particle-based robots are fabricated through chemical conjugation and magnetic self-assembly, rather than existing methods that use specialized chemistry and lithography methods, sometimes including the use of molds and elastomeric materials.

“Such simple microswimmers circumvent the technical limitations of fabrication technologies, which effectively allow for a focus on the functionalization of microswimmers,” said Kim. “Furthermore, the use of particles to create these microswimmers will synergize well with other micro- and nanoparticle–based technologies such as nanoparticle drug delivery systems.”

The locomotion method works by exploiting the negligible inertial forces found at low Reynolds numbers in a fluid. That is, as viscous forces become dominant, the robots rely on nonreciprocal motion created by their rotation.

With a strong electromagnetic system fixed to a microscope surrounding the microrobots’ chamber, Kim noted they were able to exert fine control over the swimmers.

“Our results demonstrated successful control over the microswimmers’ swimming speed and direction. The significance of the results is the demonstration that such extremely simple microswimmers can be fully controllable at low Reynolds number,” Kim added. 

An example of the application of Kim’s work in microrobotics. (Video courtesy of Drexel University.)

Kim hopes to expand on the research by systematically investigating the particle size and application of the tiny bots.

As technological limitations are broken down, medical technology comes closer to noninvasive surgeries using nanotechnology. Using these technologies to assist existing surgical methods— or to deliver specific dosages of drugs within the human body—would change the way we handle medicine and potentially expand the human lifespan further than we already have.