Microrobots have been developed and demonstrated to deliver drugs within the human body but typically can target only easily accessible sites. A new device designed at Max Planck Institute for Intelligent Systems, Germany, expands the reach of drug-carrying bots by enabling them to traverse the circulatory system and move with as well as against the flow of blood.

These microrollers navigate blood vessels by rolling along and adhering to their walls where blood flow is slower. Steered by an external magnetic field, the microrollers move against the bloodstream, which has been a The microbots roll along the inner walls of blood vessels, even against the flow of blood. Source: Max Planck Institute for Intelligent Systemschallenge for bots of this size. The microbots are similar in size, shape and locomotion capabilities as leukocytes — white blood cells — and feature a chamber that can be loaded with drugs and a surface to which antibodies can be attached.

One side of the leukocyte-inspired spherical microrollers is coated with gold and nickel layers to facilitate manipulation by magnetic field. An anticancer drug and antibodies are applied to the other side to steer the microroller toward tumor cells. Magnetic propulsion and steering of the 3 to 8 μm diameter spheres in an artificial blood vessel resulted in translational motion speeds up to 600 μm/second.

The microbots are not yet ready for human clinical trials, as the drug cargo transported by one such device is not of sufficient therapeutic strength. A swarm of microrollers must be activated to provide any required dose of medicine.