For precise, straightforward tasks, unnecessary complexity is the enemy. That's why scientists at Drexel University are working to design smaller, simpler microrobots.

Researchers say the minimalist robots could be used for tissue incision or and to puncture retinal veins.

The newly unveiled microbots are designed to swim, replicating a fluid motion in the simplest manner possible.

The swimming microbots consist of two conjoined magnetic microbeads coated in iron oxide debris. To combine the microparticles, scientists prepare two sets, coating one in avidin and the other in biotin -- a pair of proteins that form one of the strongest natural non-covalent bonds. Magnetic debris is then adhered to microstructures on the surface of the microparticles.

Previous microbot production techniques have mostly relied on sophisticated chemistry and lithography, which require 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," MinJun Kim, a professor of mechanical engineering at Drexel, explained in a news release. "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."

Researchers used magnetic forces to spin the microbots in way that converts rotational motion into translational motion and moves the swimmers through a fluid. By mounting an electromagnetic coil system onto a microscope, scientists were able to precisely manipulate the strength, direction and rotational frequency of the magnetic field.

The secret to the robots' swimming success is propulsion at low speeds. High spin rates could disturb the fluid medium too much, and the microbots' maneuverability would be thwarted. Scientists used fluid dynamics to determine the ideal low Reynolds number -- the proper ratio of forces that ensure a low degree of turbulence.

They published their findings in a new paper, which appeared this week in the journal Applied Physics Letters.

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