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Tiny voyagers, made in India

- In a lab, propellers swim through blood

New Delhi, July 5: Indian scientists have developed tiny propellers that can swim through human blood and demonstrated for the first time in a laboratory an idea conceived decades ago for applications in medical diagnosis and therapy.

The researchers at the Indian Institute of Science (IISc), Bangalore, have fabricated corkscrew-shaped, metal-coated magnetic glass propellers so small that over 200 could fit on the top of an average-sized full-stop at the end of a sentence.

Their experiments suggest the propellers could be guided at will using rotational magnetic fields.

“We’re calling them nanovoyagers,” said Ambarish Ghosh, a physicist at the IISc who led the research, published in the journal Nano Letters.

“We’re hoping they will some day help diagnose diseases and deliver medicines precisely where they’re needed in the human body.”

The idea of microscopic machines in medicine has been circulating in scientific circles for decades. The late American physicist and Nobel laureate Richard Feynman, in a seminal lecture delivered in December 1959, envisioned what he said was a “wild idea” of patients swallowing their surgeons.

“You put the mechanical surgeon inside the blood vessel and it goes into the heart and looks around.... It finds out which valve is the faulty one and takes a little knife and slices it out. Other small machines might be permanently incorporated in the body to assist some inadequately functioning organ,” Feynman had said in a talk many physicists view as a landmark in advances towards nanotechnology.

Over the past decade, research groups in the US, Europe, Japan and China have taken steps towards building tiny machines and fabricating propellers and functional nanomotors that are powered by chemicals, magnetic fields or even sound waves for propulsion through fluids.

But most of these machines have been shown to work primarily in processed water or serum, not in pure, undiluted human blood.

“Human blood can be extremely corrosive to the materials used in making microscopic machines,” Ghosh told The Telegraph.

“At such tiny scales, the concentration of chlorides and phosphates in blood destroy the delicate metallic materials within minutes.”

Ghosh and his colleagues crafted their microscopic propellers from silicon, the material in glass, and coated it with different sets of magnetic metallic materials.

They observed that the propeller rotates and moves forward when exposed to an external rotating magnetic field. Their experiments represent the “first successful voyage of artificial nanomotors in human blood”, the IISc researchers wrote in their research paper.

They observed speeds up to 15 micrometres a second, and the propellers survived exposure to human blood for over 12 hours. The scientists say the speed may be increased by tweaking the propellers’ geometry and magnetic make-up.

“This is a beautiful example of work in the emerging field of self-propelled nanomotors,” said Ayusman Sen, emeritus professor at the Pennsylvania State University in the US who was not associated with the IISc work but is widely viewed as a pioneer in nanomachine research.

Self-propelled nanomotors are promising candidates for the next generation of drug delivery systems.

Conventional drugs are metabolised in the liver and pass through the bloodstream before they reach their target sites. Self-propelled motors that may be tagged with equally small drug-filled capsules are intended to home in on specific sites in the body — such as cancer cells — and deposit the drugs only where they are needed.

“But a big challenge ahead will be to find ways to control self-propelled motors without any external power source,” Sen told this newspaper.

“Ideally, what we want is for such nanomotors to sense a biochemical in the body and go straight to it.”

IISc research scholars Pooyath Lekshmy Venugopalan, Ranajit Sai, and Yashoda Chandorkar, and faculty members Bikramjit Basu and Srinivasrao Shivashankar worked with Ghosh, combining bits of materials science, electrical engineering and physics to develop the propellers.

Materials science experts also caution that nanomachine technology is still a nascent field and probably at least a decade away from routine applications in medicine.

“Such devices will need to be rigorously tested for toxicity before they are sent into the human body,” said Ramesh Chandra Bhudani, a physicist and director of the National Physical Laboratory, New Delhi.