It’s long been known that micro vs. macro physics have thwarted some efforts to create micro components and assemblies. The study of Newtonian (fixed viscosity) and Non-Newtonian fluids (variable viscosity) fluids have an unique impact on developing and scaling drug delivery devices and body-fluid flow. Non-Newtonian fluids can be found in the blood, the eye, and in joint fluid and micro implants, swallowable devices, and tiny motion devices can be helped along with a change in viscosity.
This research also brings 3d printing and micro molding technologies together, which will happen more and more as the 3d printing and materials very quickly are developed. Isometric is excited to be positioned well in this market space. Kudos to Max Planck Institute for their incredible research!
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.
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 shows some animations and descriptions of the microscallop swimmers and their unique propulsion system.
The research was published in the journal Nature Communications.
Source: Max Planck Institute