In a unique feat, researchers at the Indian Institute of Science (IISc) in Bangalore have developed 'nano-swimmers' that can be steered through human blood and a variety of other biological fluids using an external magnetic field1.
The collaborative work by a team of IISc physicists, material scientists and electrical engineers could be an essential step towards realising physicist Richard Feynman's decades-old prophecy that someday doctors would send nano robots cruising through blood vessels to coduct microsurgery or deliver disease-treating drugs.
The swimmers are made of silica and covered in a layer of magnetic coating so that their motion can be controlled from outside by a small and homogeneous rotating magnetic field. Dubbed 'nano voyagers', these tiny swimmers could potentially open doors to a range of biomedical applications.
"The holy grail would be to use these voyagers for targeted drug delivery and microsurgery under in-vivo conditions," physicist Ambarish Ghosh, one of the corresponding authors of the report, told Nature India. "We still have a long way to go."
Most nano swimmers realised to date by workers elsewhere were actuated in de-ionized water, in human serum and saliva. There has not been a successful voyage of externally driven nano motors in undiluted blood because of two challenges this posed, says Ghosh.
One important requirement for a nano motor to swim in human blood is that the thrust it generates should be big enough to overcome viscous drag due to the thickness and stickiness of blood and resistance offered by blood cells. Secondly, according to Ghosh, the large concentration of chloride and phosphate ions in blood can eat away the magnetic coating necessitating another protective cover around the nano motor. Finding a suitable second coating that remains stable for several hours proved to be one of the biggest challenges faced by the IISc researchers.
They overcame these hurdles by using a 'conformal ferrite' coating over the magnetic nano helices. The nano swimmers were also put through cell culture tests to confirm that the coating is non-toxic – an essential criterion to realise future biomedical applications.
"These coatings were found to be stable in various bio-fluids, even after overnight incubation, and did not have significant influence on the propulsion efficiency of the magnetically driven nano helices, thereby facilitating the first successful “voyage” of artificial nano motors in human blood," Ghosh said. The authors believe that the conformal ferrite coating developed for this study can be incorporated in other designs of nano motors as well.
The team is now conducting 'in-vitro sensing' and therapeutic 'proof-of-principle' experiments. "Our next aim, in collaboration with cancer biologists, is to check the motion of the nano voyagers in cancerous tissue, and test its potential for cancer diagnostics and drug delivery."
1. Venugopalan, P.Y. et al. Conformal cytocompatible ferrite coatings facilitate the realisation of a nanovoyager in human blood. Nano Lett. 14, 1968–1975 (2014) doi: 10.1021/nl404815q