Nano necklace to mimic micro-locomotion

Mimicking how some micro organisms move in fluids with their cilia and flagella, a group of researchers have created an artificial necklace1 of microscopic beads that can move on their own

in fluids without any external propulsion force1. The 'active beads' necklace could have promising applications in targeted drug delivery and in mimicking sperm propulsion to solve fertility

issues.

At a micro scale, locomotion is a challenge since viscous forces are overwhelmingly large and the flapping of a fin-like object produces no forward motion. Thus, bacteria and spermatazoa

have evolved special organs like cilia and flagella which overcome the physical constraints imposed by motion at that scale.

A major goal in bioengineering has been to design synthetic objects capable of mimicking the motion of cila and flagella, thus serving as artificial locomotion organs. The medical

applications of such synthetic organs are immediate: attached to a small capsule they could guide the delivery of a drug to a specific location in the body, leading to more effective

therapy. Research on how to make active beads — objects that can move in fluids — is an exciting area of biomimetics today.

The researchers have now come up with a minimalistic theoretical model for 'micro oars' which will help in designing syntheticand bio-mimetic micro propulsion mechanisms. By extensive

computation on supercomputers, the researchers have shown that a collection of active beads, when strung together by a linking molecule like DNA, begin to move coherently, showing exactly

the same motions as cilia or flagella.

The model is based on a string of 'active particles', sub micron sized objects that can convert chemical energy into mechanical work. When such beads are strung together to make an active

filament and suspended in a fluid, each bead creates an active stress field in the fluid around it. The resulting velocity field result in beads interacting with each other leading to a

coherent motion of the whole system. The researchers have now found that when clamped at one end, these filaments can spontaneously exhibit flagella like cork-screw or cilia like in plane

beating.

"We have been able to provide a design, which now needs verification through laboratory work, to mimic one of nature's engineering marvels — organs that overcome the huge viscous forces

presented to a micron scale creature moving in a viscous fluid," says one of the researchers Ronojoy Adhikari.

The team is now trying to forge collaborations with experimental groups abroad to synthesise such biomimetic necklaces. "We hope that our design will soon be realised in the lab and will

make a difference to drug delivery in the future," Adhikari says.