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India forges nano-necklace - Micro device may aid pinpoint drug delivery

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  • Published 18.06.13
(From left) Team members Sunil Kumar, Rajeev Singh, Somdeb Ghose, Abhrajit Laskar, Mangal Pandi, Ronojoy Adhikari and Gayathri Jayaraman

New Delhi, June 17: A microscopic necklace designed by Indian scientists could boost efforts to build motors to propel tiny ferry boats through the human bloodstream and deliver medicines precisely where needed.

Researchers in Chennai have shown that the necklace they’ve designed and studied exclusively through a supercomputer can spontaneously display rhythmic whip-like oscillations or corkscrew-like rotations without any external power source.

Site-specific delivery of medicines, a longstanding goal in pharmacology, is expected to improve therapeutic outcomes by reducing the risk of side effects and increasing the amount of drug that reaches target tissues.

Over the past decade, scientists in European and North American laboratories have designed experimental structures to serve as propulsion systems for tiny drug-delivery capsules they hope can be programmed to carry medicines to specific sites in the body.

Some research groups have worked with the so-called chemo-mechanically active materials that can convert chemical energy into mechanical energy, and have created structures that show straight-line or oscillatory movements. But scientists are still racing to find ideal miniature propulsion systems.

Now, the Chennai researchers have shown that stringing together a necklace using tiny beads made of chemo-mechanically active materials can generate complex movements that, they say, could be harnessed for efficient propulsion.

“We’ve provided the engineering equivalent of pistons to convert straight-line motion into oscillatory motion,” Ronojoy Adhikari, a physicist at the Institute of Mathematical Sciences, Chennai, and member of the research team, told The Telegraph.

“We believe the ease of fabrication of such beads and the simplicity of the necklace-like structure should make this an attractive design strategy.”

The scientists described their design this week in the journal Scientific Reports.

“It has been a challenge to demonstrate whip-like oscillatory or corkscrew-like rotational motion using such materials,” Thomas Mallouk, professor of materials chemistry and physics at the Pennsylvania State University in the US, told this newspaper.

Six years ago, Mallouk, collaborating with Calcutta-educated chemist Ayusman Sen, also at the Pennsylvania State University, experimentally demonstrated that metallic nanorods — half-gold and half-platinum, only 0.0003mm in length — display straight-line motion when immersed in a solution of hydrogen peroxide.

Adhikari and his colleagues digitally strung together 100 of these nanorods, or beads, using biological material as thread to design a necklace 0.03mm long that displayed oscillatory and rotational movements.

“The collective behaviour of 100 beads in a fluid is different from that of an individual bead. Collectively, they mimic the movements we see in biological structures such as the tails of sperm cells or the flagella of bacteria,” said P.B. Sunil Kumar, a physicist at IIT Madras, another team member.

Scientists caution that such computer simulations will need to be authenticated through independent synthesis and experimental observations of such necklace-like structures.

Mallouk said the findings suggest new designs for motors that would use fuel much more efficiently and thus have a broader range of applications.

“More efficient motors could use bio-friendly fuel such as glucose or oxygen rather than having to rely on toxic substances like hydrogen peroxide,” he said.

“Constructing motors that combine chemical propulsion and flagella-like dynamics is an exciting research area that could lead to new design principles for molecular motors for cargo transport in small-scale systems,” Raymond Kapral, a scientist at the University of Toronto, told this newspaper.

Three years ago, Kapral and his colleagues had designed an artificial flagellum (a whip-like structure) made up of a chemically active head bead and many tail beads, each of which acts as a motor to propel the chain.

But, Kapral said, their simulations suggested that some tail motions could hinder (the intended) motion in certain instances if the chain movements were not as organised as those described by the Chennai team.

“We don’t get disorganised tail motion; it’s always corkscrew or whip-like, and thus could provide efficient propulsion engines,” said Adhikari. His students Somdeb Ghose, Abhrajit Laskar, Gayathri Jayaraman and Rajeev Singh participated in the study.

The researchers say it may be possible to use a necklace as a propeller for a drug-delivery capsule that could be guided to target sites in the body through other mechanisms.

One possibility, Adhikari said, is to introduce a bit of magnetic material into the drug-delivery capsule and use multiple magnetic fields from a magnetic resonance imaging (MRI) machine to guide the capsule to the target site.