The drive to make the Fantastic Voyage reality
A new propulsion system could drive remote-controlled nano-bots to repair our bodies from the inside. Iddo Genuth reports.
In the 1966 film Fantastic Voyage a submarine manned by scientists is miniaturised and injected into the bloodstream of a stroke victim so the scientists can travel to his brain and remove the clot. Science may not yet be able to shrink people but a team of researchers has just taken the first step towards a remote-controlled craft that might well carry out this type of fantastic voyage unmanned.
Researchers from Israel’s Technion Institute of Technology, Germany’s Max Planck Institute and the University of Stuttgart recently reported in the journal ACS Nano the creation of what they say are the world’s smallest controllable nanopropellers. The tiny devices are the size of a virus – 70 nanometres in diameter – and can travel several times their own length each second.
The device was inspired by the bacterium E. coli which is propelled by rotating whip-like flagella only a few dozen nanometres in diameter [see Microbe Masterpieces]. Ever since electron microscopes first revealed its structure in 1973 scientists have been intrigued by the idea of replicating it.
In the past 10 years a number of groups have started turning science fiction into reality. In one pre-clinical study led by Bradley Nelson from ETH University in Zurich, scientists performed animal tests using their own magnetic micro-robots to treat eye diseases such as macular degeneration and blockages in the retina’s blood vessels. These larger bots can access the surface of the retina or the lining of blood vessels.
But to access cells in other parts of the body robots need to be smaller than 100 nanometres. Any bigger and they cannot penetrate the dense mesh of molecular fibres that glue cells together into tissues, fluids such as the mucous which lines the stomach, or the fluid in the eye.
Peer Fischer’s group at the Max Planck Institute in Germany, a member of the team, has demonstrated so-called “nanoscrews” smaller than 100 nanometres that cleanly pass through the molecular mesh. The propeller helices, resembling bacterial flagella, are made of silica while their tips contain magnetic material. By applying relatively weak rotating magnetic fields they are able to achieve “contactless rotation of the ‘nanoscrews’ that propels it through the medium, says Fischer. This type of movement might also allow them to punch through solid tumours, which are notoriously hard for drugs to access.
Alexander Leshansky from the Technion University, who headed the theoretical side of the study, explained that at the nanoscale water presents a viscous barrier. The miniaturised submarine from the Fantastic Voyage would never work in real life, he says. That is why bacteria use long corkscrew-like flagella rather than conventional propellers.
The ultimate goal of the research is the development of a drug delivery system that can be guided into tumour cells without effecting nearby healthy cells. This is “elegant work”, says nano-engineer Joe Wang of the University of California, San Diego. He says it represents a major step towards practical biomedical applications of nanoscale artificial swimmers.