Researchers from Purdue University have developed magnetic ‘millirobots’ which can climb slopes, move against a current, and deliver substances to rodent neural tissue with great precision.

The study investigated how the robots – ‘Magnetically Aligned Nanorods In Alginate CapsuleS’ (aka ‘Maniacs’) – could perform as drug delivery vehicles inside the body. It found that, when controlled using a magnetic field, the robots can move against fluid flow, climb slopes and move through neural tissue, such as the spinal cord, to deposit substances at precise locations.

Disease in the central nervous system can be very difficult to treat. Lamar Mair of Weinberg Medical Physics, which partnered with the academics on the study, explained: “Delivering drugs orally or intravenously, for example, to target cancers or neurologic diseases, may affect regions of the body and nervous system that are unrelated to the disease. Targeted drug delivery may lead to improved efficacy and reduced side-effects due to lower off-target dosing.”

One way to target dosing is to use tiny robots which enter the body to deliver drugs to specific locations; a technology which is now emerging after years of speculation. The major challenge in developing useful drug delivery robots is in controlling their activity as they travel through tissues to their destination. Few researchers have put their soft, tumbling robots to the challenge in real tissues.

The Purdue University and Weinberg Medical Physics scientists used magnetic fields to control their robots, as they are not influenced by tissues and tend to be completely safe. Applying an external magnetic field, they can control the ‘Maniac’ robots, which contain magnetic nanorods encased in a soft spherical shell. The robots safely tumble through the body towards a target site for drug delivery.

The researchers put their robots to the test under the challenging conditions they may experience in the body; the architecture of the nervous system is ‘undulating and tortuous’, with flowing cerebral spinal fluid and steep slopes. They obtained rat brains and mouse spinal cords to assess the ability of the robots to move along the tissues and separately tested their ability to climb slopes and move against the current of a flowing liquid.

They found that the robots could be manoeuvred around the rodent neural tissues with a fine degree of control and deposit the dye in the desired location, even returning to ‘re-dose’ that spot. They could scale slopes as steep as 45° and were able to swim against a current similar to that which they would encounter in the nervous system.

“The ability to go back and re-dose regions which received insufficient dose upon initial treatment is significant,” said Professor David Cappelleri. “These results are very preliminary and highly experimental, but we think we have demonstrated strong evidence that small, soft capsule-based microrobots have potential for controlled local delivery in neural diseases.”