Scientists from Chennai have provided the scheme for building tiny objects that can propel themselves in fluids, like the bloodstream, to deliver drugs. The scheme is supported by simulations of how such engines would work. Their work was recently published in Nature Scientific Reports.

Professors P.B. Sunil Kumar of Physics Department, IIT Madras and Ronojoy Adhikari of Institute of Mathematical Sciences, Chennai, senior authors of the paper, wanted to design a micro-oar which would “beat” on its own and so propel anything that it was attached to. They wanted their oar to mimic the motion of cilia and flagella, the beating parts which propel bacteria in a fluid.

While sperms and some bacteria moving in fluids with the help of flagella use cork-screw-like beats to propel themselves through the system, some other protozoans like paramecium use a flexible oar-like movement. 

The researchers came up with a simple design to mimic these systems, which uses active beads, strung together in a chain. These beads convert chemical energy to mechanical motion. Such beads have been synthesised a decade ago.

Simulating the motion of the filament of active beads on a supercomputer, the research group found a remarkably life-like beating. Depending on how much flow the active beads could generate, the filament spontaneously beat like a cilium or the tail of a sperm cell, or, rotated like the flagellum of bacteria such as E. coli.

Thus, the same filament could either be used as an oar or a propeller by tuning the degree to which the beads of the chain consume chemical energy. “This new design for propulsion engines which can both beat and rotate is simpler than anything that has been suggested before” says Prof. Adhikari.

Remarking on the significance of the study, Prof. Kumar, says, “You cannot take the rules for swimming used by a large animal and apply it to a small object. 

“That is why a bacterium uses a corkscrew like motion to propel itself, instead of strokes that a swimmer would use. So when people try to build nanomotors they have to think about all this.” 

The group intends to collaborate with experimental groups to see if these systems can be realised in practice and then maybe even move on to designing drug delivery systems.

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