With the help of small magnetic rods and a rotating magnetic field, scientists were able to mimic the undulating movement of hair-like structures on cell surfaces.
Thanks to the coordinated fluctuation of hair-like structures known as cilia, the single-celled paramecium can move around its aquatic environment at a speed of ten times its own length per second. Human lungs also have cilia, and the movement of these cilia facilitates the removal of mucus. The fluid-shifting ability of cilia is something microfluidic researchers want to emulate for new devices, but they have had difficulty making synthetic cilia at the microscale. Now, researchers led by Jaap den Toonder from Eindhoven University of Technology in the Netherlands have shown how poorly artificial eyelashes can mimic the functions of real eyelashes. Additionally, their research revealed specific cilia movement properties that cause fluid redistribution.
Bundles of microtubules and additional specialized proteins form natural cilia. Their synchronized stretching is controlled by a bucket brigade of signaling molecules that cause one cilium to stretch immediately after its neighbor. The resulting pattern, known as metachrony, resembles a crowd wave in a stadium. Researchers can mimic this collective motion in synthetic eyelashes using a time-varying magnetic field. The cilia in this model are flexible rods made of a paramagnetic material arranged in an array on a surface.
The cilia respond by bending in the direction of the field as it moves across the array, like an airport radar scanning the sky. To bring this idea to life two years ago, Den Toonder and his team used a conveyor belt containing an array of magnets to set the rods in motion. But the magnets and rods were about 10 mm in size, which is three times larger than a normal cilium.
The team's latest experiment managed to reduce the size to two orders of magnitude, and it is possible to shrink it even further. The unique method in which the magnetic field directs the artificial eyelashes allowed the system to be miniaturized. The scientists used traditional methods to create the 150 µm-long cilia from paramagnetic carbonyl iron.
They then glued collections of these cilia to a plastic substrate placed on top of a cylinder of paramagnetic material. When the system was exposed to a rotating magnetic field due to the cylinder distorting the field lines, each cilium experienced a different magnetic field at any given time. Each cilium responded by bending forward and then retracting elastically when this local field rotated from strong to weak. Using simulation software, the timing of the field fluctuations was adjusted so that a wave passed through the array.
Den Toonder and his team used a video camera mounted on a microscope to confirm that their miniature artificial eyelashes moved in a metachronal manner.
But can cilia move fluid? In this case, how? This question is more nuanced than it seems at first glance. It is possible that both the whip-like motion of individual cilia and their collective metachronal waves cause fluid motion. Additionally, if the back and forth strokes of a cilium are symmetrical, the cilium cannot produce net fluid motion independently.
The scientists created a microfluidic device out of clear plastic and filled it with two liquids at a time: water and glycerol, respectively, to simulate a low-viscosity liquid and the other a high-viscosity liquid to get the answers. In addition, they investigated two different types of cilia arrays, one in which the wave propagates in the same direction as the forward bending direction, and the other in which they contradict each other.
These two states, called symplectic and antiplectic, respectively, correspond to the two main categories of metachronal movements seen in naturally occurring cilia. When the paramagnetic cylinder was removed from the assembly, the cilia oscillated back and forth without producing a metachronal wave, but the rotation field remained constant.
By examining the film, the scientists were able to track the wiper tip movement for both the forward, magnetically generated stroke and the backward, elastic restoring stroke. They found that the magnetic stroke took up more space than the elastic stroke in all different situations, indicating that the magnetic stroke was more important in creating flow. In fact, the measured fluid flow for the high viscosity fluid was forward.
However, in low viscosity fluid the elastic beat was significantly faster than the magnetic one, and this whip-like motion caused backward flow. It has been discovered that metachronal motion distorts the flow created by cilia in both fluids, promoting antiplectic metachrony and disrupting symplectic metachrony.
The findings demonstrate the diverse contributions that individual and group silt movement can make to flow formation. This information could be useful for future attempts to incorporate synthetic cilia into small microfluidic chips, according to the researchers. They also predict that synthetic eyelashes can be shrunk even further to the size of natural eyelashes, allowing studies of whether they work to regulate the liquid environments of cells and tissues.
Source: physics aps org
📩 13/09/2023 09:12