Microrobots have future in targeted therapy

SPERM-inspired microrobots, consisting solely of a head coated in a thick cobalt-nickel layer and an uncoated tail, have been developed by team of researchers at the University of Twente and the German University in Cairo. The 322 micron-long robots, which can be controlled by oscillating weak magnetic fields, are described in a cover article* in the journal Applied Physics Letters from AIP Publishing.

When the microrobot is subjected to an oscillating field of less than five millitesla – about the strength of a decorative refrigerator magnet – it experiences a magnetic torque on its head, which causes its flagellum to oscillate and propel it forward. Directing the magnetic field lines towards a reference point allowed the researchers to steer the robot.

Islam Khalil, an assistant professor of the German University in Cairo (GUC), designed the MagnetoSperm microrobots along with Sarthak Misra and colleagues at MIRA-Institute for Biomedical Technology and Technical Medicine at the University of Twente.

The microrobot was made by spin-coating onto a silicon support wafer a five-micron layer of SU-8, a polymer chosen for its ease of fabrication and mechanical stability. The cobalt-nickel layer was then added to the head by use of electron beam evaporation.

“Nature has designed efficient tools for locomotion at micro-scales. Our microrobots are either inspired from nature or directly use living micro-organisms such as magnetotactic bacteria and sperm cells for complex micro-manipulation and targeted therapy tasks,” Dr. Misra, the principal investigator and an associate professor at the University of Twente, said.

Dr. Khalil noted that as technology progresses and many products get smaller, it becomes difficult to assemble objects on nano- and micro-scales. “MagnetoSperm can be used to manipulate and assemble objects at these scales using an external source of magnetic field to control its motion,” he said.

The radical downsizing afforded by the offloading of power and navigation systems also opens up a wide range of biomedical tasks that MagnetoSperm can perform, Dr. Khalil said. These include targeted drug delivery, in vitro fertilization, cell sorting and cleaning of clogged arteries, among others.

In the future, the researchers hope to further scale down the size of MagnetoSperm. The team is currently working on a method to generate a magnetic nanofiber that can be used as a flagellum.

* Islam S. M. Khalil, Herman C. Dijkslag, Leon Abelmann and Sarthak Misra. "MagnetoSperm: A Microrobot that Navigates using Weak Magnetic Fields" Applied Physics Letters (DOI: 10.1063/1.4880035).