Scallop microbots designed to swim through your bodily fluids

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Researchers have been experimenting with real micro-sized robots that literally swim through your bodily fluids (Image: Max Planck Institute)

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In the 1960s science fiction film Fantastic Voyage, audiences thrilled to the idea of shrinking a submarine and the people inside it to microscopic dimensions and injecting it into a person’s bloodstream. At the time it was just fantasy and as fantastic an idea as its title suggested. Today, however, micro-miniature travelers in your body have come one step closer to reality. Researchers from the Max Planck Institute have been experimenting with real micro-sized robots that literally swim through your bodily fluids and could be used to deliver drugs or other medical relief in a highly-targeted way.

The microrobots being designed by the team literally are swimmers; they are scallop-like devices designed to paddle through non-Newtonian fluids like blood and plasma (even water behaves in this way at a microscopic level). This means that, unlike swimming in water at a macro-level, these microbots need to move through fluid that has a changing viscosity depending on how much force is exerted upon it.

To do this, the microbots need a method of propulsion that can fit in their tiny bodies as well as take advantage of the non-Newtonian fluid in which they are moving. Importantly, the team is using a reciprocal method of movement to propel their microscallops; but generally this doesn’t work in such fluids, which is why organisms that move around in a biological system use non-reciprocating devices like flagella or cilia to get about.

However these robotic microswimmers actually take advantage of this property and use a scallop swimming motion to move around. The researchers call this process "modulation of the fluid viscosity upon varying the shear rate." In simple terms, the micro scallops open and close their "shells" to compress the fluid and force it out behind them, which then propels them along.

"The shell is only a few times larger than the thickness of a human hair," said Professor Peer Fischer, leader of the Micro, Nano and Molecular Systems Research Group. "A liquid like water is about as viscous for these devices as honey or even tar is for us."

The research team used ferromagnetic actuators (basically magnetically-operated hinges) to open and close their shells under the influence of an applied external alternating magnetic field – on to close, off to open. Do this often enough and quickly enough, and the microrobot scallop can swim at speed across – say – your eyeball.

The fact that the microrobot scallop has no motor to drag around contributes to its exceptionally small size – around 800 microns. This makes it miniscule enough to make its way through your bloodstream, around your lymphatic system, or across the slippery goo on the surface of your eyeballs. And, not only are they small, but their simplicity makes them ideal to be printed on a 3D printer.

Apart from the obvious use in delivering a product in a targeted way to parts of the body inaccessible by conventional methods, the team has yet to elucidate any other uses for their swimming microscallop robots. However, if they get the devices small and agile enough, it’s fairly likely that many in the medical world will find a way to exploit their properties to the benefit of patients.

The video below shows some animations and descriptions of the microscallop swimmers and their unique propulsion system.

The research was published in the journal Nature Communications.

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